WO2002103461A2 - A method and a system for embedding textual forensic information - Google Patents

Abstract

A method for automatically embedding information in a digital text, said method comprising: identifying a plurality of positions, in said digital text, that are suitable for introducing modifications into said digital text; identifying modifications suitable for introduction into at least some of said suitable positions in said digital text; selecting at least some of said identified modifications for introduction into said digital text, said selection of said modifications being operable to represent said information; and performing said selected modifications on said digital text, thereby to embed said information.

Description

A METHOD AND A SYSTEM FOR EMBEDDING TEXTUAL

FORENSIC INFORMATION

FIELD OF THE INVENTION

The present invention relates generally to the field of securing

digital content. More specifically, the present invention deals with

forensic methods for breach analysis and business espionage mitigation.

BACKGROUND OF THE INVENTION

Modern businesses and industries relay heavily on digital content

as a primary mean of communication and documentation. Digital content

can be easily copied and distributed (e.g., via e-mail, instant messaging,

peer-to-peer networks, FTP and web-sites), which greatly increase

hazards such as business espionage and data leakage. There is therefore

great interest in methods that would mitigate risks of digital espionage

and unauthorized dissemination of proprietary information.

In general, one can divide the counter digital espionage methods

into two categories: proactive methods, that increase the difficulty of

unauthorized copying and distribution of digital documents, and reactive methods, the latter providing means for detection and tracking of

breached content, for forensic purposes and for tracking and incrimination

of suspects, thereby to provide an effective deterrence. '

Current attempts to automatically mitigate espionage are focused

on proactive methods. While these methods can be helpful in some cases,

it is generally believed that any proactive method may be eventually

circumvented, and there is a strong need to complement these methods

with reactive means, that provide for forensic evidence and a means for

incrimination of suspects. An effective forensic measure should provide

an effective means to determine the exact source of a breached document.

In the context of secure distribution of multimedia content, some

forensic methods require that unique, personalized digital watermarks,

dubbed "fingerprint", be embedded into each copy of the data before it is

sent to the final user, allowing for binding of each copy with an

authorized and accountable user. Numerous methods for personalized

watermarking of multimedia files, such as video and audio contents, exist:

in these cases, there exists a high level of redundancy that allows

embedding of watermarks into the media, in a manner that will not reduce

the quality of the media and yet will be robust to both malicious and non-

malicious attacks. Some methods for embedding steganograms (hidden

messages) inside a text also exist, and can be traced back to far antiquity.

However, since the amount of redundancy in text is much smaller then

the redundancy in audio or video, it is harder to embed in a robust manner such hidden messages in a text, in particular if the embedding process is

to be done automatically, and current methods for automatic embedding

of steganograms in text are usually based on altering the number of

spaces in the end of line, which are highly vulnerable to format changing.

In many cases, documents are prepared by groups, where each

member of the group introduces his own modifications into a document.

An efficient document forensic system should consider this fact, and

embed modifications that are as robust as possible against casual editing

while allowing for seamless group-working on copies that contain

somewhat different versions of the documents.

Embedding steganograms into text is also important for copyright

protection of digital books: Illegal copying and distribution of digital

books, also known as "e-books", has been prevalent in recent years,

especially using the Internet. This illegal copying and distribution is an

infringement of copyright protection laws and cause financial damage to

the rightful owners of the content. It is therefore of great interest to find

methods that would stop or at least reduce illegal copying and/or

distribution of digital texts without offending rightful usage. To-date, no

such method is in use.

Another important aspect of a forensic technique is robustness: a

forensic method should be robust against consequential changes in the

substance and preferably against deliberate attempts to remove the

forensic marks. Current methods usually lack an adequate level of robustness.

Prior art regarding usage of forensic data for tracking breaches and

espionage detection include the usage of manual insertion of small

modifications in various copies of the document, as well as the insertion

of identification data in the meta-data of the binary file and altering the

number of spaces in the end of the lines of the text. Such methods do not

provide an adequate solution to the problem of modern businesses, since

the rate of production of copies of digital documents renders the cost of

manual insertion of modifications prohibitive, and the plurality of formats

in which the information can be represented render metadata based

methods ineffective, since file metadata is often altered when the format

of the file is changed.

There is thus a recognized need for, and it would be highly

advantageous to have, a method and system that allow personalized

watermarking of text in digital documents, which will overcome the

drawbacks of current methods as described above.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is

provided a method for automatically embedding information in a digital

text, the method comprising:

identifying a plurality of positions, in the digital text, that are

suitable for introducing modifications into the digital text;

identifying modifications suitable for introduction into at least

some of the suitable positions in the digital text;

selecting at least some of the identified modifications for

introduction into the digital text, the selection of the modifications being

operable to represent the information; and

performing the selected modifications on the digital text, thereby

to embed the information.

In a preferred embodiment of the present invention, the method

further comprises the approval of the selection of modifications in the

digital text.

In a preferred embodiment of the present invention, the

modifications include at least one of the following:

replacing a character with a substantially similar looking character;

replacing a character with a similarly looking character, where the

characters only differ in their digital representation;

replacing a character with a similarly looking character, where the characters only differ in their Unicode representation;

removing an unprintable character;

adding an unprintable character;

replacing an unprintable character;

5 exchanging between at least two possible representations of an end

of a paragraph; and exchanging between at least two possible

representations of an end of a line.

In a preferred embodiment of the present invention, the

modifications include at least one of the following:

l o modifying the number of spaces between words ;

modifying the number of spaces between paragraphs;

modifying the number of spaces between lines;

modifying the number of spaces at a line ending;

modifying the number of tabs at a line ending;

15 adding at least one space character at a line ending;

adding at least one tab character at a line ending;

modifying the size of spaces between words;

modifying the size of spaces between paragraphs;

modifying the size of spaces between lines;

0 modifying the size of spaces between characters;

modifying the number of spaces representing a tab character;

modifying the place of a tab;

replacing a tab character with at least one space; replacing at least one space with a tab character; and modifying the

size of a tab character.

In a preferred embodiment of the present invention, the

modifications include at least one of the following:

modifying the font of at least one character;

modifying the color of at least one character;

modifying the size of at least one character;

modifying a property of at least one character;

modifying the background of the digital text;

modifying the background of at least one character;

replacing a character with an image similar to the character;

modifying the digital representation of the digital content;

modifying the internal logical division in the digital representation

of the digital content;

modifying the classification of a unit in the internal logical "

division in the digital representation of the digital content;

modifying a property of a unit in the internal logical division in the

digital representation of the digital content;

modifying the classification of a paragraph; and modifying a

property of a paragraph.

In a preferred embodiment of the present invention, the

modifications include at least one of the following:

punctuation modifications; spelling modifications;

spelling modifications that exchange between different valid

spellings of the same word; and spelling modifications that exchange

between at least one valid spelling of the a word and at least one invalid

spelling of the word.

In a preferred embodiment of the present invention, the

modifications include at least one of the following:

exchanging between some of the following versions of a word

built from at least two words: a concatenated version, a version that uses a

hyphen for separation and a version separated by a space;

spelling modifications that exchange between an acronym and full

verbatim versions of the acronym;

spelling modifications that exchange between at least one

shortened version of a word and the full version of the word;

exchanging between a correct version of a word and at least one

other word, the other words have similar pronunciation to the correct

word;

exchanges between synonyms;

modifications that effect an order of elements within the digital

text;

modifications that effect an order of words;

modifications that effect an order of sentences; and modifications

that effect an order of paragraphs. In a preferred embodiment of the present invention, the

modifications include at least one of the following:

modifications that effect capitalization;

removing at least one word;

adding at least one word;

replacing at least one word;

modifications to diagrams embedded in the digital text;

addition of diagrams embedded in the digital text;

removal of diagrams embedded in the digital text;

modifications to the shadow of at least one character;

exchanging between at least two different grammatical structures;

and modifying the phrasing of at least a part of the digital text such that

the changed version remains similar to the original version.

In a preferred embodiment of the present invention, the

identification of modifications is performed in a manner which takes into

consideration limitations imposed by the digital representation of the

digital text.

In a preferred embodiment of the present invention, the embedded

information contains information suitable to identify at least one entry in

a database, the database entry containing additional information.

In a preferred embodiment of the present invention, the embedded

information contains information operable to identify at least one

recipient of the digital text. In a preferred embodiment of the present invention, the method

further comprises the step of selecting different combinations of the

modifications to form different copies of the digital text such that a

plurality of recipients of the digital text each receive a personally

modified version of the digital text, the different combinations within the

embedded information being operable to uniquely identify a respective

recipient of each copy.

In a preferred embodiment of the present invention, the embedded

information contains information operable to identify at least one editor

of the digital text.

In a preferred embodiment of the present invention, the method

further comprises automatically performing the step of identifying

positions in the digital text.

In a preferred embodiment of the present invention, the step of

identifying positions in the digital text, is performed manually.

In a preferred embodiment of the present invention, the step of

identifying positions in the digital text, is perfoπned such that the

positions are distributed in a predefined manner within the digital text.

In a preferred embodiment of the present invention, the predefined

manner of distribution of the positions within the digital text is a

distribution where all portions of the digital text larger than a given size

contain enough embedded information to reconstruct a predetermined

subset of the embedded information. In a preferred embodiment of the present invention, the desirable

manner of distribution of the positions within the digital text is a

distribution defined such that removal of a significant number of the

positions from the digital text results in significant degradation of the

value of the digital text.

In a preferred embodiment of the present invention, at least part of

the embedded information is encoded using at least one of the following:

error detection code;

error correction code;

cryptographic signature; and

cryptographic encryption.

In a preferred embodiment of the present invention, the

identification of suitable modifications is performed in a manner which

takes into account the limitations imposed by requirements concerning

the quality of the digital text and on the resemblance of the modified text

to the original version of the digital text.

In a preferred embodiment of the present invention, the selection

of the identified modifications is performed so that at least two potential

modifications are grouped together, and where several versions of the

digital text are produced with different embedded information, the group

of changes being performed in unison, such that if a modification which

is part of the group is performed on one version of the text, all other

modifications in the group are also performed on the version. In a preferred embodiment of the present invention, the

modifications in the group are in proximity to each other within the

digital text.

In a preferred embodiment of the present invention, the selection

of modifications is performed such as to take into account the amount of

information which is to be embedded in the digital text.

In a preferred embodiment of the present invention, the amount of

information which is to be embedded in the digital text is dictated by at

least one of the following considerations:

the amount of actual information which needs to be represented by

the information embedded in the digital text;

the usage of error correction code;

the usage of error detection code;

the requirements on robustness;

the required number of different versions of the digital text;

the need to embed a database index; and

the need to embed versioning information.

In a preferred embodiment of the present invention, the embedded

infoπnation contains at least one of the following:

versioning information;

editing history information;

forensics information;

transfer history information; and infoπnation operable to identify and categorize the digital text.

In a preferred embodiment of the present invention, the embedded

information is substantially imperceptible.

According to a second aspect of the present invention there is

provided A method for monitoring digital text by utilizing information

embedded in digital texts, the method comprising:

embedding information in digital texts it is desired to monitor;

detecting an attempt to use a specific digital text;

determining whether the specific digital text contains the

embedded information;

determining whether the specific digital text is one of the digital

texts it is desired to monitor according to the embedded information; and

reading the information embedded in the specific digital text.

In a preferred embodiment of the present invention, the embedded

information is operable to identify the source of the digital text when the

digital text is found in at least one of the following states:

in the possession of an unauthorized party;

in an unauthorized location;

in an unsecured location; and

in an unsecured format.

In a preferred embodiment of the present invention, the embedded

information is further operable to identify at least part of the path in

which the digital text reached the state. In a preferred embodiment of the present invention, the method

further comprises controlling the usage of the digital text according to the

embedded information.

In a preferred embodiment of the present invention, the embedded

information contains at least one limitation about the usage of the digital

text.

In a preferred embodiment of the present invention, the limitations

comprising at least one of the following:

limitations about the time in which it is allowable to use the digital

text;

limitations about where it is allowable to use the digital text;

limitations about how it is allowable to use the digital text; and

limitations about who is allowed to use the digital text.

In a preferred embodiment of the present invention, the

controlling is dependent on at least one of the following:

the identity of the user performing the usage;

the usage rights of the user performing the usage;

the identity of the digital text;

the risks associated with the usage;

the security mechanisms used in the usage; and

the type of usage.

In a preferred embodiment of the present invention, the limitations

on how the text is used comprise limitations to at least one of the following:

viewing the digital text;

editing the digital text;

transferring the digital text; and

storing the digital text.

There is also provided in accordance to a prefered embodiment of

the present invention A system for controlling usage of a digital text by

utilizing information embedded in digital text the system comprising:

at least one computerized information embedding unit operable to

embed the inforaiation in the digital texts;

at least one computerized information reading unit operable to read

the information embedded in the digital texts;

at least one computerized digital text usage unit operable to use the

digital texts; and

at least one computerized control unit operable to:

receive notification from the computerized digital text usage unit,

the notification indicating the digital text;

receive information from the computerized information reading

unit, the information dependent on the information embedded in the

digital text and read by the computerized infoπnation reading unit; and

instruct the computerized digital text usage unit on a usage policy

for the digital text, the usage policy dependent on the information

received from the computerized information reading unit. In a preferred embodiment of the present invention, the embedded

information is operable to identify the source of the digital text when the

digital text is found in the possession of an unauthorized party.

In a preferred embodiment of the present invention, the system

further comprises at least one database containing at least one entry

containing additional information, and where the embedded information

is operable to be coπelated to the entry.

In a preferred embodiment of the present invention, the system

further comprises at least one computerized document management unit

operable to maintain information about digital texts.

In a preferred embodiment of the present invention, the

computerized document management unit is operable to maintain at least

one of the following types of information:

versioning information;

editing history information;

usage policy infoπnation;

transfer history information; and

category information.

In a prefeπed embodiment of the present invention, the

computerized document management system is operable to interact with

the computerized control unit.

In a preferred embodiment of the present invention, the interaction

comprises at least one of the following: the computerized control unit informing the computerized

document management unit about usage of the digital text; and

the computerized document management unit sending information

to the computerized control unit, the infomiation sent operable to be used

by the computerized control unit to create the usage policy.

In a preferred embodiment of the present invention, the usage

policy comprises at least one of the following:

preventing the usage;

restricting the usage;

monitoring the usage;

reporting the usage; and

allowing the usage.

In a preferred embodiment of the present invention, the usage

policy depends on at least one of the following:

the identity of the user performing the usage;

the usage rights of the user performing the usage;

the identity of the digital text;

the identity of the editors of the version of the digital text used in

the usage;

the risks associated with the usage;

the security mechanisms used in the usage; and

the type of usage. In a preferred embodiment of the present invention, the usage

comprises at least one of the following:

viewing the digital text;

editing the digital text;

transfeπing the digital text; and

storing the digital text.

In a prefeπed embodiment of the present invention, the embedded

information contains first indication infoπnation, the first indication

information indicating at least one element in a group, and where the

embedded infoπnation further contains second indication information, the

second indication information indicating the group.

In a preferred embodiment of the present invention, the embedded

information contains a plurality of information elements, and where a

subset of the information elements are embedded into the digital text such

that the subset of the information elements is encoded in a manner more

resilient to a change in the digital text than the embedding of another

subset of the information elements.

In a prefeπed embodiment of the present invention, the system

further comprises a computerized transformer unit operable to receive a

version of a digital text, the version contains both editing changes and

embedded information, and where the computerized transformer unit is

further operable to produce a version of the digital text which contains

both the editing changes and different embedded information. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with

reference to the accompanying drawings. With specific reference now to

the drawings in detail, it is stressed that the particulars shown are by way

of example and for purposes of illustrative discussion of the preferred

embodiments of the present invention only, and are presented in the cause

of providing what is believed to be the most useful and readily understood

description of the principles and conceptual aspects of the invention. In

this regard, no attempt is made to show structural details of the invention

in more detail than is necessary for a fundamental understanding of the

invention, the description taken with the drawings making apparent to

those skilled in the art how the several forms of the invention may be

embodied in practice.

In the drawings:

Fig. 1 is a flow-chart showing the sequence of steps for the

insertion of forensic information in digital textual document, constructed

and operative in accordance with a preferred embodiment of the present

invention;

Fig. 2 is a flow-chart showing the sequence of steps for creation of

personalized text documents, constructed and operative in accordance

with a prefeπed embodiment of the present invention; Fig. 3 is an illustration of a simplified pre-versioning system,

constructed and operative in accordance with a prefeπed embodiment of

the preent invention;

Fig. 4 is a flow-chart showing the sequence of steps for embedding

hidden messages into a digital textual document, constructed and

operative in accordance with a prefeπed embodiment of the present

invention;

Fig. 5 is a flow-chart showing the sequence steps for marking and

pre-encryption of a set of data segments, constructed and operative in

accordance with a prefeπed embodiment of the present invention,

Fig. 6 is a simplified block-diagram describing group working on

personalized documents, as part of a prefeπed embodiment of the present

invention;

Fig. 7 is a simplified block diagram that represents the function of

the version generator, in accordance with a prefeπed embodiment of the

present invention;

Fig. 8, is a simplified diagram showing a hidden information

reading unit, constructed and operative according to a prefeπed

embodiment of the present invention, and

Fig. 9 is a simplified diagram illustrating a digital text usage

control system, constructed and operative according to a prefeπed

embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention seeks to provide a system and a method for

on-line, real-time personalized marking of digital content, with an

emphasis on text, in order to allow tracking and detection of sources of

leaks and breaches of confidential and proprietary information, thereby

mitigating the hazards of digital espionage and unauthorized

dissemination of proprietary information.. The system and the methods

can also be used as a part of a digital rights management system.

According to a first aspect of the present invention, a method

based on distributing a preferably unique copy to each of the recipients,

thereby allowing tracing and detecting the sources of breaches, is

described. In a prefeπed embodiment of the invented method, a

technique for maintaining the coherency and integrity of the personalized

documents while working in groups is also described.

Before explaining at least one embodiment of the invention in

detail, it is to be understood that the invention is not limited in its

application to the details of construction and the aπangement of the

components set forth in the following description or illustrated in the

drawings. The invention is capable of other embodiments or of being

practiced or caπied out in various ways. In addition, it is to be

understood that the phraseology and terminology employed herein is for

the purpose of description and should not be regarded as limiting.

Reference is first made to figure 1, which is a simplified flowchart of the basic steps in practicing a prefeπed embodiment of the present

invention: The original document or text is presented to the system (stage

A, as indicated by 110) and undergoes an automatic versioning phase in

which several personalized versions of the original document or text are

created, based on modifying elements of the text or the document, (stage

B, as indicated by 120). For each of the versions a version descriptor is

created (stage C, as indicated by 130). The version descriptor and

corresponding recipient are then inserted to a database (stage D, as

indicated by 140) and the personalized versions are then distributed to the

various recipients (stage E, as indicated by 150).

Some examples for modifying techniques operable for versioning

are:

• Punctuation: additional/missing comas, replacing commas

"," with semi-colons ";" and vice versa, concatenation of sentences, usage

of ", which" versus "that", usage of parentheses instead of commas and

vice-versa etc.

• Spelling: if there is more then one way to spell a word (e.g.,

color/colour, can not /cannot, foreign words, names, etc.) then such a

word is a candidate for modifying.

• Exact synonyms, i.e., words that can be replaced with other

words without causing appreciable change (e.g., "for example" instead of

"e.g.")-

• Altering the number or size of spaces between words, lines and characters.

• Altering some properties of some of the fonts.

• Deliberate typos, especially in homophonic words.

• Rephrasing of sentences and sub-sentences.

• Rephrasing of paragraphs.

• Capitalization (e.g. after ":")

• Additional words.

• Replacing a character with a substantially similar looking

character;

• Replacing a character with a similarly looking character,

wherein said characters only differ in their digital representation;

• Replacing a character with a similarly looking character,

wherein said characters only differ in their Unicode representation;

• Removing an unprintable character;

• Adding an unprintable character;

• Replacing an unprintable character;

• Exchanging between possible representations at an end of a

paragraph;

Exchanging between possible representations at an end of a

line;

Modifying the number of spaces between paragraphs;

Modifying the number of spaces at a line ending;

Modifying the number of tabs at a line ending; • Adding a space character at a line ending;

• Adding a tab character at a line ending;

• Modifying the size of spaces between paragraphs;

• Modifying the size of spaces between lines;

• Modifying the number of spaces representing a tab

character;

• Modifying the place of a tab;

• Replacing a tab character with at least one space;

• Replacing a space with a tab character;

• Modifying the size of a tab character;

• Modifying the font of a character;

• Modifying the color of a character;

• Modifying the size of a character;

• Modifying a property of a character;

• Modifying the background of the digital text;

• Modifying the background of a character;

• Replacing a character with an image similar to a character;

• Modifying the digital representation of the digital content;

• Modifying the internal logical division in the digital

representation of the digital content;

• Modifying the classification of a unit in the internal logical

division in the digital representation of the digital content; • Modifying a property of a unit in the internal logical

division in the digital representation of the digital content;

• Modifying the classification of a paragraph;

• Modifying a property of a paragraph .

• Exchanging between some of the following:

• versions of a word built from at least two words:

o a concatenated version,

o a version that uses a hyphen for separation, and

o a version separated by a space;

• Spelling modifications that exchange between an acronym

and a full verbatim versions of said acronym;

• Spelling modifications that exchange between at least one

shortened version of a word and the full version of said

word;

• Modifications that exchange between a coπect version of a

word and at least one other word, the other words having

similar pronunciation to the coπect word;

• Exchange between synonyms;

• Modifications that effect order of elements within said

digital text;

• Modifications that effect the order of words;

• Modifications that effect the order of sentences;

• Modifications that effect the order of paragraphs; Modifications that effect capitalization;

Removing a word;

Adding a word;

Replacing a word;

Modifications to diagrams embedded in the digital text;

Addition of diagrams embedded in the digital text;

Removal of diagrams embedded in the digital text;

Modifications to the shadow of a character;

Exchanging between different grammatical structures;

• Modifying the phrasing of a part of the digital text such that

the changed version retains its similarity to the original version.

The position of potential candidates for modifying can be

performed either manually or by using specialized software.

In another aspect of the present invention, another level of marking

can be added, by using watermarks on the background of the text, and in

particular, the portion of the background behind words.

In general, not all the modifying process operable for versioning

would have the same merit: for example, deliberate typos reduce the

quality of the document and are susceptible to spelling coπection.

Altering some properties of fonts and size of spaces between characters

may not be robust against format changing etc. One can therefore define

strength, or robustness parameter to each modification, as well as a

quality factor that will define to what extent the modifying process reduces the quality of the content.

Figure 2 illustrate a flowchart of the process of preparing versions

of various segments, according to a prefeπed embodiment of the present

invention. At the first step, candidates for modifying are located (stage

A, as indicated by 210), after that, two or more modifications of each of

the segments is produced, e.g., using one or more of the methods

described above or the more extensive list of versioning techniques

described elsewhere in this disclosure, (stage B, as indicated by 220). The

modifications are preferably undergone a stage of approval, either

manually (e.g., by the author of the text) and/or automatically (e.g., by

another software component). The stage of approval is indicated as stage

C, as indicated by reference numeral 230 in Fig. 2). Each of the approved

modifications is then identified by a modification identifier (stage D, as

indicated by 240) and is stored in a library on a storage device (stage E, as

indicated by 250).

Reference is now made to figure 3, which illustrates a process in

which a set of modifications of a certain position is constructed and stored

according to a prefeπed embodiment of the present invention. The

position denoted by B, indicated by 304, is used by the modifying

subsystem 308 in order to produce the modifications together with the

coπesponding identifier and descriptor: modification Bl, indicated by

310, modification B2, indicated by 312 and modification B3, indicated by

314. The modifications, together with the coπesponding identifier and descriptor are then stored in the storage device 316 for future usage.

The modifying process can also be done by grouping together

several optional modifications into one set of logical symbols. The

cardinality of this set is the product of the number of modifications in

each optional position. E.g., if, within the group, there are four possible

modifications for punctuation, three possible synonyms for a given word

and two possible spellings, then there are total of 4*3 *2b = 24 possible

modifications in the group. If we assign a logical symbol to each version,

then the cardinality of the set of symbols is 24.

Grouping of optional modifications may also be based on their

order within the text. In this case, the content can be divided into

segments, and the possible modifications within each segment may be

grouped together to form a set of logical symbols. Each symbol in a set

for a given segment is unique from each other symbol in the set. Sets of

pre-versioned data segments associated with different segments of the

salient fraction may, but are not required to, contain segments with the

same symbols. That is, each set contains an "alphabet" of logical

symbols that may or may not be the same alphabet as symbols contained

within other sets associated with other segments. For example, a set

associated with a first data segment may contain logical symbols "A","B"

and "C," while a set associated with a second segment may contain

symbols "C", "1" and "3". All the sets of pre-encrypted data segments

are refeπed to as a library. In general, it is advantageous to be able to identify a versioned

copy based on a small portion of the text. In order to achieve that goal,

the modifications between copies should be distributed along the text as

uniformly as possible.

As content is prepared for distribution to an authorized user

according to the present embodiments, a unique copy of the content,

which is preferably correlated with some aspects of the details of

authorized user, is produced. The unique content is preferably produced

by selecting a specific sequence of modifications of the various positions.

Denoting the j-th modification of the i-th modification by V(i,j), a

personalized version is created by selecting the sequence V(l,kι), V(2,k₂),

V(3,k₃), V(4,k₄)..., where the sequence kj k^.._.. , which determines which

modification in each position is selected, provides a unique

characterization of the personalized copy. The desired document may

then be produced by inserting the coπesponding version of each segment

in the appropriate position.

The method may also be used to robustly embed other (not

necessarily unique) information.

Turning now to Fig. 4, there is shown a block diagram of the steps

for preparing a text to on-line version system that allows a series of

uniquely identifiable individual versions of a text to be produced,

distributed and then uniquely identified. At the first stage (stage A, as

indicated by 410), the number of required copies, N, is defined. At the next stage (stage B, as indicated by 420), an optimized scheme for

creation of N sequences of modifications is evaluated. In general, an

optimal scheme would be such that the N copies are as remote as possible

from one another, i.e., that it would be as hard as possible to make one

personalized version indistinguishable from another, in the sense that the

number of modifications, weighted by the robustness factor is maximal,

while keeping the quality of the versions as high as possible. Such a

notion of an optimal scheme is known from the domain of error-

coπecting code. The optimization process may be based on exhaustive

search or on a more structured search process in the combinatorial space.

After defining the optimal scheme, N different copies, with N

different sequences of modifications are produced (staged C, indicated as

430). To each of the personalized version an indicator is attached, that

may be coπelated with some details of the recipients (staged D, indicated

as 440). The copies are then distributed to the various recipients (stage E,

indicated as 450) and the list of recipients, together with the

coπesponding descriptors, are stored in a database for further usage

(stage F, indicated as 460). Such further usage may for example include

identifying the source of a version that was distributed without an

authorization and the like.

Figure 5 schematically illustrates a document system for managing

the creation and distribution of individualized versions of documents,

which is refeπed to hereinafter as system 500. According to the configuration illustrated in Figure 5, System 500 includes a version

generator 510, which is preferably monitored by the document system

interface 520. The original text created by the original text creator 530, is

sent to the version generator 510, which produces versioned copies 540,

such that any recipient may obtain a different version of the document.

The version generator also sends the descriptors of the various versions to

the database 560. The version handler 550 obtains information that

characterizes the differences between the various versions and the

original text. The database 560 obtains the version descriptors and the

correlations between versions and recipients, in order to allow tracking

and detection of the breached documents.

The version handler 540 handles cases in which versioned text

documents are transfeπed between recipients and/or to the original

creator. The version handler compares the versions of the sender and the

recipient, and modifies the sender's version accordingly, thereby allowing

seamless group work on the document. In another prefeπed embodiment

of the present invention the information is embedded in a cryptographic

format (encrypted and/or signed) thereby preventing certain harmful

scenarios, such as framing of an innocent user. This encryption and/or

signing should be made to the data before using any kind of eπor

correction encoding, since otherwise the eπor coπection code may be

rendered ineffective.

Note that when using a database, embedding may be done in advance and the database entry may be updated after a pre embedded

copy is allocated to a certain recipient.

Reference is now made to figure 6, which is a simplified scheme

of a prefeπed embodiment of the version handler 540, which allows

group working on versioned documents using document-handling system

500. The sender 610, who whishes to send his working version 620 to a

recipient 630 with working version 640, sends his working copy to the

comparator 670 and the transformer 680. The comparator 670 compares

the versioned text 620 with the reference version of the text 690 in order

to locate the modifications that characterized the sender version, and

which still remain after the edit changes in the document that the sender

might introduce while working on his version of the document. The

transformer 680 preferably uses data from the database 660 and the

comparator 670 in order to transform the personalization scheme of the

sender to a personalization scheme of the recipient, in a transparent or

seamless manner. This is implemented by first removing the specific

personalized modifications that were introduced by the version generator

and which may still remain in the sender working version, and then

producing the modifications to characterize the recipient copy which

would have still remained in the working version of the sender had they

been there in the beginning.

Note that if the original personalization scheme was rendered

ineffective due to substantial changes in the original text that a writer introduces in his/her copy, then the changed text itself may contain a

sufficient level of differences, which enables the identification of the

copy.

An alternative approach may consist of taking advantage of the

fact that changes to the text are usually localized. This can either be done

by using a specialized eπor coπection code designed for coπecting

localized eπors, or by embedding a simple eπor detection code on

localized chunks of data (e.g. paragraphs), and verifying them before

extraction of the embedded information (prefeπing the eπorless chunks

for extraction) A prior (and in many cases alternative) step may be to look

for similarities between chunks in order to know what is the origin of

chunks in order to ease the practice of verifying the chunks.

In order to reduce the ability of malicious tampering by recipients,

it may be beneficial to embed personalized information for each subgroup

of recipients or to some of those subgroups, where the embedding of

information for said subgroups should be independent, instead of

embedding personalized information on each copy for each recipient.

Thus if a subgroup of recipients attempts to remove the specific

information for its members by comparing their respective copies, and

attempting to remove the infoπnation identified as differences, they still

can be identified by the subgroup's information, which will be identical in

all their copies. In certain cases, embed personalized information for each

(proper or otherwise) subgroup of recipients or to some of those subgroups (the embedding of information for said subgroups should be

independent) personalized information may become redundant; because

an individual recipient may be uniquely identified by the intersection of

the subgroups, she (or he) is member of.

Note that some attacks on the content may consist of canonizing

the text in some manner, thus it is of great benefit to embed the

watermark independently using a number of methods, or with an eπor

coπection code that is designed to handle a complete removal of all

information encoded using some of the methods. Thereby create enough

redundancy in order to mitigate most canonizing attacks.

Turning now to figure 7, there is illustrated a block diagram that

represents the function of the version generator, in accordance with a

prefeπed embodiment of the present invention. The version generator 510

of the document-handling system 500 gets as inputs the original text, the

required number of versions, the minimal distance between versions and

the allowed depth of versioning, where "deeper versioning" refer to more

substantial modifications in the text. The policy manager 720 provides

rules regarding which modifications require an approval from the creator

or an authorized party (e.g. operator, administrator). If an approval is

required, the user interface 730 prompt the user with a suggestion for

modifications and asks for approval. The data storage 740 contains all the

approved modifications that can be used for versioning. The total possible

number of personalized copies is the product of the number of modifications of each optional position. E.g., if, within a paragraph there

are four possible modifications for punctuation, three possible synonyms

for a given word and two possible spellings of another given word, then

there are total of 4*3*2 = 24 possible versions. In order to provide for a

sufficient level of redundancy, which is needed for eπor coπection and

robustness, the total number of possible versions should be significantly

larger then the required number of versions, such that between any two

different users, the minimal number of modifications would exceed a

certain threshold value Θ, which may be provided by the user or an

authorized party (e.g. operator, administrator). If the total number of

possible versions is significantly larger then the required number of

versions, then it is probably sufficient to create the various versions by

randomly selected between the possible modifications using the random

selector 750 and checking afterwards that the minimal distance is indeed

larger then Θ using the testing module 760. Otherwise one can use one of

the numerous eπor-coπection codes available. The modifications that

characterize each version are stored in the database 770.

It is important to note that the aforementioned level is not a linear

scale, but rather a set of allowed methods and restrictions for using those

methods (e.g. no more than 2 typos in a paragraph).

Note that the impact of modifications may be application, or

context depended - e.g., modifications in punctuation in a source code of

a computer program may affect the result of its compilation and may cause it to cease functioning altogether - e.g. by causing a syntax eπor.

It is also important to note, that in some applications there may not

be as many degrees of freedom as needed to satisfy the set constraints,

which may result in either changing or reducing constraints

(automatically, manually or a combination of both), or a failure to embed

all the necessary data (either embedding partial information, or none at

all). An implementation may need to address this issue according to the

specific application in question (e.g. to fail the whole versioning process,

then denying access to the text or alerting an operator that changes to the

configuration need to be made).

Also, it is noted that in general, specific handling of versions of

specialized types of text (e.g. poems and sonnets, code of specific

programming languages, spreadsheet data, a combination of several

domains, etc.) may need both classification of the type of the text, and

specialized parsing in order to identify changeable positions.

Classification of the type of the text may also be needed in order to

employ the coπect policy for handling the content

Turning now to figure 8, there is illustrated a hidden information

reading unit 800, constructed and operative according to a prefeπed

embodiment of the present invention. The document reader 810 reads the

analyzed document and the document identifier 820 attempts to identify

the document (e.g., using file meta-data or based on the textual content of

the document), preferably using the data in the database 830. If the document was found to be one on which hidden information is embedded,

then the modifications detector 840 goes over all the positions on which

two or more modifications were embedded and attempts to detect which

version was embedded. The results are then sent to the maximum

likelihood estimator 850, which estimates the likelihood of the most

probable sequences of modifications that comprise the hidden

information. This is especially important in cases where the document has

undergone substantial changes due to editing and/or malicious attacks.

The decision unit 860 use the likelihood information in order to decide

which hidden information is embedded in the analyzed document, and

possibly also to determine the personalized version that is most likely to

be the source of the analyzed document. The output from the reader is

provided in the form of embedded information.

Turning now to figure 9, there is illustrated a digital text usage

control system 900, constructed and operative according to a preferred

embodiment of the present invention. The embedded information-reading

unit 800 reads digital text 910. Usage control unit 920 obtains information

from the information reading unit 800 and determines permitted usage of

the digital text 910. The permitted usage is typically one or more of the

following: viewing the digital text, editing the digital text, transfeπing the

digital text and storing the digital text. The usage control unit 920 then

instructs the digital text usage unit 930 whether to allow a requested

usage 940. Other limitations may include the following: limitations about the

time in which it is allowable to use the digital text; limitations about

where it is allowable to use the digital text; limitations about how it is

allowable to use the digital text; and limitations about who is allowed to

use the digital text.

The usage limitations may be contingent on any one of a number

of factors including the following: the identity of the user; usage rights

granted to the user; the identity or nature of the digital text; the risks

associated with the usage; the security mechanisms used involved in

using the text; and the type of usage that is being attempted. Thus, for

example very different usage regimes are likely where the main concern

is copyright violation or where the main concern is the leaking out of

commercially sensitive infoπnation or of sensitive security information.

In another embodiment of the present invention, the information is

embedded in the text in a manner that does not require actual use of the

original document or of any other reference document in order to read the

embedded information In the wateπnark embedding literature, this

method is referred to as an oblivious reading. To illustrate the

implementation of such a method, one may consider each occuπence of

"that" being replaced by "which" or vice versa, as a place in which a bit is

embedded, and consider an occurrence of "that" in this position as "1"

and an occuπence of "which" as "0". The message is encoded using an

error-detection code and an eπor-coπection code, so that only a very small fraction of the possible strings of zeros and ones are legitimate.

While reading, the reader renders a string of ones and zeros. If the string

is legitimate, then it is assumed that the detected message was indeed

embedded in the text. Thus the investigation of legitimacy is caπied out

without reference to another version. Note that oblivious methods are, by

nature, less robust then non-oblivious methods. These methods enable

avoiding or at least reducing usage of databases and are especially useful

when embedding is done in a distributed manner without the ability to

contact a central database. An alternative approach is to use a distributed

scheme where multiple databases are used, and where the embedded

information also contains the index of the database.

In another embodiment of the present invention, the embedded

information is used as a reactive measure for copyright protection of

digital books ("e-books") and other copyrighted textual content. The

embedded information can be used as forensic measure in order to trace

an authorized user that distributes textual content in an unauthorized

manner, thereby providing an effective deteπence against unauthorized

distribution.

It is appreciated that one or more steps of any of the methods

described herein may be implemented in a different order than that

shown, while not departing from the spirit and scope of the invention. While the present invention may or may not have been described

with reference to specific hardware or software, the present invention has

been described in a manner sufficient to enable persons having ordinary

skill in the art to readily adapt commercially available hardware and

software as may be needed to reduce any of the embodiments of the

present invention to practice without undue experimentation and using

conventional techniques.

While the present invention has been described with reference to

one or more specific embodiments, the description is intended to be

illustrative of the invention as a whole and is not to be construed as

limiting the invention to the embodiments shown. It is appreciated that

various modifications may occur to those skilled in the art that, while not

specifically shown herein, are nevertheless within the true spirit and

scope of the invention.

Claims

Claims:We claim:

1. A method for automatically embedding information in a digital

text, said method comprising:

identifying a plurality of positions, in said digital text, that are

suitable for introducing modifications into said digital text;

identifying modifications suitable for introduction into at least

some of said suitable positions in said digital text;

selecting at least some of said identified modifications for

introduction into said digital text, said selection of said modifications

being operable to represent said infomiation; and

performing said selected modifications on said digital text, thereby

to embed said information.

2. A method according to claim 1, wherein said method further

comprises the approval of said selection of modifications in said digital

text.

3. A method according to claim 1, wherein said modifications

include at least one of the following:

replacing a character with a substantially similar looking character;

replacing a character with a similarly looking character, wherein

said characters only differ in their digital representation; replacing a character with a similarly looking character, wherein

said characters only differ in their Unicode representation;

removing an unprintable character;

adding an unprintable character;

replacing an unprintable character;

exchanging between at least two possible representations of an end

of a paragraph; and

exchanging between at least two possible representations of an end

of a line .

4. A method according to claim 3, wherein said modifications

include at least one of the following:

modifying the number of spaces between words;

modifying the number of spaces between paragraphs;

modifying the number of spaces between lines;

modifying the number of spaces at a line ending;

modifying the number of tabs at a line ending;

adding at least one space character at a line ending;

adding at least one tab character at a line ending;

modifying the size of spaces between words;

modifying the size of spaces between paragraphs;

modifying the size of spaces between lines;

modifying the size of spaces between characters; modifying the number of spaces representing a tab character;

modifying the place of a tab;

replacing a tab character with at least one space;

replacing at least one space with a tab character; and

modifying the size of a tab character .

5. A method according to claim 1, wherein said modifications

include at least one of the following:

modifying the font of at least one character;

modifying the color of at least one character;

modifying the size of at least one character;

modifying a property of at least one character;

modifying the background of said digital text;

modifying the background of at least one character;

replacing a character with an image similar to said character;

modifying the digital representation of said digital content;

modifying the internal logical division in the digital representation

of said digital content;

modifying the classification of a unit in the internal logical

division in the digital representation of said digital content;

modifying a property of a unit in the internal logical division in the

digital representation of said digital content;

modifying the classification of a paragraph; and modifying a property of a paragraph .

6. A method according to claim 1, wherein said modifications

include at least one of the following:

punctuation modifications;

spelling modifications;

spelling modifications that exchange between different valid

spellings of the same word; and

spelling modifications that exchange between at least one valid

spelling of the a word and at least one invalid spelling of said word .

7. A method according to claim 1, wherein said modifications

include at least one of the following:

exchanging between some of the following versions of a word

built from at least two words: a concatenated version, a version that uses a

hyphen for separation and a version separated by a space;

spelling modifications that exchange between an acronym and full

verbatim versions of said acronym;

spelling modifications that exchange between at least one

shortened version of a word and the full version of said word;

exchanging between a coπect version of a word and at least one

other word, said other words have similar pronunciation to said coπect

word; exchanges between synonyms;

modifications that effect an order of elements within said digital

text;

modifications that effect an order of words;

modifications that effect an order of sentences; and

modifications that effect an order of paragraphs .

8. A method according to claim 1, wherein said modifications

include at least one of the following:

modifications that effect capitalization;

removing at least one word;

adding at least one word;

replacing at least one word;

modifications to diagrams embedded in said digital text;

addition of diagrams embedded in said digital text;

removal of diagrams embedded in said digital text;

modifications to the shadow of at least one character;

exchanging between at least two different grammatical stractures;

and

modifying the phrasing of at least a part of said digital text such

that the changed version remains similar to the original version .

9. A method according to claim 1, wherein said identification of

modifications is performed in a manner which takes into consideration

limitations imposed by the digital representation of said digital text.

10. A method according to claim 1, wherein said embedded

information contains information suitable to identify at least one entry in

a database, said database entry containing additional information.

11. A method according to claim 1, wherein said embedded

information contains information operable to identify at least one

recipient of said digital text.

12. A method according to claim 11, comprising the step of

selecting different combinations of said modifications to form different

copies of said digital text such that a plurality of recipients of said digital

text each receive a personally modified version of said digital text, said

different combinations within said embedded information being operable

to uniquely identify a respective recipient of each copy.

13. A method according to claim 1, wherein said embedded

information contains information operable to identify at least one editor

of said digital text.

14. A method according to claim 1, comprising automatically

performing said step of identifying positions in said digital text.

15. A method according to claim 1, wherein said step of

identifying positions in said digital text, is performed manually.

16. A method according to claim 1, wherein said step of

identifying positions in said digital text, is performed such that said

positions are distributed in a predefined manner within said digital text.

17. A method according to claim 16, wherein said predefined

manner of distribution of said positions within said digital text is a

distribution wherein all portions of said digital text larger than a given

size contain enough embedded information to reconstruct a predetermined

subset of said embedded information.

18. A method according to claim 16, wherein said desirable

manner of distribution of said positions within said digital text is a

distribution defined such that removal of a significant number of said

positions from said digital text results in significant degradation of the

value of said digital text.

19. A method according to claim 1, wherein at least part of said

embedded information is encoded using at least one of the following:

eπor detection code;

eπor coπection code;

cryptographic signature; and

cryptographic encryption .

20. A method according to claim 1, wherein said identification of

suitable modifications is performed in a manner which takes into account

the limitations imposed by requirements concerning the quality of said

digital text and on the resemblance of said modified text to the original

version of said digital text.

21. A method according to claim 1 , wherein said selection of said

identified modifications is performed so that at least two potential

modifications are grouped together, and wherein several versions of said

digital text are produced with different embedded information, said group

of changes being performed in unison, such that if a modification which

is part of said group is performed on one version of said text, all other

modifications in said group are also performed on said version.

22. A method according to claim 21, wherein said modifications

in said group are in proximity to each other within said digital text.

23. A method according to claim 1, wherein said selection of

modifications is performed such as to take into account the amount of

information which is to be embedded in said digital text.

24. A method according to claim 23, wherein said amount of

information which is to be embedded in said digital text is dictated by at

least one of the following considerations:

the amount of actual information which needs to be represented by

said information embedded in said digital text;

the usage of eπor coπection code;

the usage of eπor detection code;

the requirements on robustness;

the required number of different versions of said digital text;

the need to embed a database index; and

the need to embed versioning information .

25. A method according to claim 1, wherein said embedded

information contains at least one of the following:

versioning information;

editing history infoπnation;

forensics information;

transfer history infoπnation; and information operable to identify and categorize said digital text .

26. A method according to claim 3, wherein said embedded

information is substantially imperceptible.

27. A method for monitoring digital text by utilizing information

embedded in digital texts, said method comprising:

embedding information in digital texts it is desired to monitor;

detecting an attempt to use a specific digital text;

determining whether said specific digital text contains said

embedded information;

determining whether said specific digital text is one of said digital

texts it is desired to monitor according to said embedded information; and

reading said information embedded in said specific digital text .

28. A method according to claim 27, wherein said embedded

information is operable to identify the source of said digital text when

said digital text is found in at least one of the following states:

in the possession of an unauthorized party;

in an unauthorized location;

in an unsecured location; and

in an unsecured format .

29. A method according to claim 28, wherein said embedded

information is further operable to identify at least part of the path in

which said digital text reached said state.

30. A method according to claim 27, wherein said method further

comprises controlling the usage of said digital text according to said

embedded information.

31. A method according to claim 30, wherein said embedded

information contains at least one limitation about the usage of said digital

text.

32. A method according to claim 31, wherein said limitations

comprising at least one of the following:

limitations about the time in which it is allowable to use said

digital text;

limitations about where it is allowable to use said digital text;

limitations about how it is allowable to use said digital text; and

limitations about who is allowed to use said digital text.

33. A method according to claim 32, wherein said controlling is

dependent on at least one of the following:

the identity of the user performing said usage; the usage rights of the user performing said usage;

the identity of said digital text;

the risks associated with said usage;

the security mechanisms used in said usage; and

the type of usage .

34. A method according to claim 32, wherein said limitations on

how said text is used comprise limitations to at least one of the following:

viewing said digital text;

editing said digital text;

transfeπing said digital text; and

storing said digital text .

35. A system for controlling usage of a digital text by utilizing

information embedded in digital text[?s], said system comprising:

at least one computerized information embedding unit operable to

embed said information in said digital texts;

at least one computerized information reading unit operable to read

said information embedded in said digital texts;

at least one computerized digital text usage unit operable to use

said digital texts; and

at least one computerized control unit operable to: receive notification from said computerized digital text usage unit,

said notification indicating said digital text;

receive information from said computerized information reading

unit, said information dependent on said information embedded in said

digital text and read by said computerized information reading unit; and

instruct said computerized digital text usage unit on a usage policy

for said digital text, said usage policy dependent on said information

received from said computerized information reading unit .

36. A system according to claim 35, wherein said embedded

information is operable to identify the source of said digital text when

said digital text is found in the possession of an unauthorized party.

37. A system according to claim 35, wherein said system further

comprises at least one database containing at least one entry containing

additional information, and wherein said embedded information is

operable to be correlated to said entry.

38. A system according to claim 35, wherein said system further

comprises at least one computerized document management unit operable

to maintain information about digital texts.

39. A system according to claim 38, wherein said computerized

document management unit is operable to maintain at least one of the

following types of information:

versioning information;

editing history information;

usage policy information;

transfer history infoπnation; and

category information .

40. A system according to claim 38, wherein said computerized

document management system is operable to interact with said

computerized control unit.

41. A system according to claim 40, wherein said interaction

comprises at least one of the following:

said computerized control unit informing said computerized

document management unit about usage of said digital text; and

said computerized document management unit sending

information to said computerized control unit, said information sent

operable to be used by said computerized control unit to create said usage

policy .

42. A system according to claim 35, wherein said usage policy

comprises at least one of the following:

preventing said usage;

restricting said usage;

monitoring said usage;

reporting said usage; and

allowing said usage .

43. A system according to claim 35, wherein said usage policy

depends on at least one of the following:

the identity of the user performing said usage;

the usage rights of the user performing said usage;

the identity of said digital text;

the identity of the editors of the version of said digital text used in

said usage;

the risks associated with said usage;

the security mechanisms used in said usage; and

the type of usage .

44. A system according to claim 35, wherein said usage

comprises at least one of the following:

viewing said digital text;

editing said digital text; transfeπing said digital text; and

storing said digital text .

45. A system according to claim 35, wherein said embedded

information contains first indication information, said first indication

information indicating at least one element in a group, and wherein said

embedded information further contains second indication information,

said second indication infoπnation indicating said group.

46. A system according to claim 35, wherein said embedded

information contains a plurality of information elements, and wherein a

subset of said information elements are embedded into said digital text

such that said subset of said information elements is encoded in a manner

more resilient to a change in said digital text than the embedding of

another subset of said information elements.

47. A system according to claim 35, wherein said system further

comprises a computerized transformer unit operable to receive a version

of a digital text, said version contains both editing changes and embedded

information, and wherein said computerized transformer unit is further

operable to produce a version of said digital text which contains both said

editing changes and different embedded infoπnation.