CN102169535A

CN102169535A - Text steganographic method based on keyword replacement

Info

Publication number: CN102169535A
Application number: CN2011100943030A
Authority: CN
Inventors: 王勇
Original assignee: Guilin University of Electronic Technology
Current assignee: Guilin University of Electronic Technology
Priority date: 2011-04-11
Filing date: 2011-04-11
Publication date: 2011-08-31
Also published as: CN102360413B; CN102360413A

Abstract

The invention relates to a text steganographic method based on keyword replacement, in which important keywords can be replaced by the keywords desired by a sender through the replacement of two different forms of keywords so as to achieve the aim of freewill misleading. During the steganography, the keywords can be selected at will; keys are generated according to the relationship between the keywords before and after the replacement; and the original text can be extracted by a receiver according to a main key. The replaced keywords are determined by the sender, so that the replaced keywords have good pertinence and a better misleading effect and are difficult to show slips. In the opinion of a listener (opponent) that intercepts a disguised text, the sent disguised file is the original text as the text is meaningful, the file is generally meaningless after being encrypted, and the other steganographic methods such as steganography in video and audio files need multimedia files; and the receiver does not know that the original text undergoes steganography treatment and has a misleading function, and furthermore, the meaning of the disguised text is opposite to the meaning of the original text.

Description

A kind of text secret writing method of replacing based on keyword

Technical field

The invention belongs to information security field, relate to a kind of text secret writing method of replacing based on keyword.

Background technology

Steganography (secret writing art, Steganography) is a skill and a science about Information hiding, so-called Information hiding (informationhiding) refer to do not allow except that the expection the recipient anyone know the transmission incident of information or the content of information.Modern technique of secret writting mainly is to rely in the jumbo files such as image, audio frequency, video to hide Info.Also has a kind of special Information Hiding Techniques, it is the subliminal channel (subliminal channel) that nineteen eighty-three Simmons proposes, the subliminal channel of narrow sense mainly adopts digital signature to wait and realizes the message concealment, but subliminal channel can be closed, and utilizes under the threshold of digital signature transmission message back toward very short.As seen, present Information Hiding Techniques or needs rely on big file as carrier, or can only transmit very short message, camouflage text (carrier, covertext) sharp concealed text (stegotext is called original text here) is compared greatly a lot, and channel utilization is not high.Send jumbo files such as picture audio frequency, video in case be under an embargo, do not allow to carry out under the situation of digital signature, the concealment of classified information just can't realize, and the sharp subliminal channel problem of Information hiding often at be monitored because of the background violated and so on, supervision goes into can forbid fully any behavior that may hide message.We had also once designed a kind of text secret writing method that adopts stream cipher to control sub-key, but, though the camouflage text that obtains has misleading, but owing to be the key sequence that stream cipher produces, the camouflage text produces according to key sequence, can not arbitrarily remove to be provided with the camouflage text, the present invention has designed a kind of secret writing method that can mislead the other side arbitrarily.

Summary of the invention

It is big that the present invention is intended to overcome existing secret writing method amount of redundancy, depends on the shortcoming of image, speech data, provides a kind of text is carried out the method for secret writing, and can have the function of misleading.Different with encryption, the camouflage text of secret writing directly transmits, and the other side can think it is expressly, so can directly go to mislead the other side.

For possessing the misleading function, in the present invention, to have designed and adopted similar gestalt choosing to express the mode of topic secret writing, it needs a keyword database, in database, keyword similar, close, opposite or that can substitute is placed in the identical group.In the time of secret writing, open file, read the content of text, in the time of secret writing keyword is replaced to having the keyword of same nature, this keyword is close with former keyword sense, opposite or have substituting.In the time of secret writing, the secret writing system shows the keyword in all same group in this group, secret writing then can be selected, keyword in the text is replaced with in order the keyword of oneself selecting, and generate a key according to the position difference of replacing, can correctly reduce when being convenient to extract former text.Because the keyword in the text is all replaced with similar, close and opposite keyword, thereby the camouflage text has the misleading effect.

Keyword database is a basic database, in design, must forbid a keyword for the unique reversibility that guarantees secret writing and extraction and appear in two groups of keywords.Because if keyword has relation of inclusion,, also there are the Chinese people to benefit the nation altogether such as China is arranged in the keyword database.In addition, if a keyword appears in two groups of keywords of database, then encrypt sharp problem of deciphering the result that also ambiguity can be run into and can't obtain determining.For fear of ambiguity, there is not relation of inclusion between the keyword mutually in addition, coincidence can not be arranged.

When replacing, the replacement of some keyword be fix, carry out automatically, some keyword then is to come the selection of oneself following one's bent by the sender.Such misleading better effects if.

In each group keyword, have whether an attribute representative is the replacement of fixing: 1) if fixing replacement has only two speech in the group of so fixedly replacement, certainly general such replacement is a pair of antonym.2) if revocable replacement, in database, each keyword all has a numbering in this group, and from 0,1, until n-l, wherein n is the keyword number in this group.In the time of secret writing, keyword in all these groups is all shown, allow the sender select keyword wherein to replace, the relation that the system log (SYSLOG) keyword is replaced, and produce a key with this, key k=a-b mod (n), wherein a is the keyword in the original text, b is the numbering of the selected keyword of replacing.Can recover original text according to corresponding relation when can guarantee to extract original text like this.Key for fixing replacement, directly extracts the keyword of original text just at revocable replacement according to fixing corresponding relation.After secret writing is finished, will generate the sequence of a key k according to the sequence of keyword in the original text, time standby this sequence of deciphering is decrypted, and calculates a=b+k mod (n) one by one, just can determine the keyword in the original text.Maximum number max{n} according to keyword in each group in the database calculates [log2max{n}]+1, promptly can draw the least number of bits that key k coding needs, and wherein [] expression rounds.

Because secret writing itself is the form expressly that disguises oneself as, the adversary does not also know to have passed through secret writing, so the part that keyword database need to be keep secret, particularly those fixing keywords are replaced.Secret writing is different from encryption, encryption is to allow the other side know the existence of ciphering process, secret writing then should not, and the camouflage text should be one normal, significant text or image and so on, can play the effect of misleading like this, the present invention adopts keyword to replace, and the sender selects keyword to make the text of camouflage have meaning.

Because this secret writing method is just replaced content of text, therefore, secret writing for document needs first opening document, such as opening word or txt document earlier, read the content of text of the inside, again content of text is pretended to replace, the text after will replacing is at last preserved, and the process of extracting secret information then is an opposite process.

Embodiment

Illustrate below:

Suppose will carry out secret writing to a .txt text now, the content of its text is " be Monday today ".In the keyword database of system, " today ", one group of corresponding keyword was " tomorrow ", " day after tomorrow ", and replacing attribute is that on-fixed is replaced; One group of keyword of "Yes" correspondence is " not being ", and replacing attribute is fixing the replacement.

In the database in all groups maximum one group of keyword 15 keywords are arranged, can draw key k only needs 4 bits, the k that therefore sets each keyword correspondence is 4 bits.

In the time of secret writing, open text with notepad, reading of content earlier.Then one by one in text search whether keyword arranged, carry out corresponding replacement according to the attribute of keyword.Today is owing to be keyword, and is on-fixed, so, today, tomorrow, the day after tomorrow are all shown, and their corresponding codes are respectively 0,1,2, the sender selects and expresses, and selects the day after tomorrow such as the sender, then k=0-2mod (3)=1, we get 0001 as key, and it is write in top 4 bits of total key,, continue to write in order backward if there is keyword the back.Then text is continued to scan in order and search for, find that "Yes" is a keyword, and for fixing replacement, so directly "Yes" is replaced with " not being ".Obtain pretending text " be not Monday the day after tomorrow ", deposit text in txt file, as the camouflage text, total key is 0001.

When extracting original text, open text, read " be not Monday the day after tomorrow ", search in text, be keyword the day after tomorrow, so read top 4 bits in total key, 0001, be numbered 2, a=2+1 mod (3)=0 in the day after tomorrow this group in database, be numbered 0 keyword, i.e. today so get.Then searching " not being " is keyword, according to attribute, directly it is reduced to and is.Therefore, can obtain original text and be " be Monday today ", deposit it in txt file, promptly obtain source document.

Claims

1. text secret writing method of replacing based on keyword, it is characterized in that it being secret writing at text, with File Open, read text, carry out certain keyword and replace since the speech of replacing may be close in meaning with original speech, opposite and similar, the text after the replacement still has meaning, and may with original be close in meaning, opposite, make it to have the function of random misleading.

2. text secret writing method of replacing based on keyword as claimed in claim 1 is characterized in that directly a keyword being replaced with the keyword of stipulating in the database when fixing replacement, need not to generate key, extracts original text and need not to utilize key.

3. text secret writing method of replacing as claimed in claim 1 based on keyword, it is characterized in that when carrying out the on-fixed replacement, the sender can directly select oneself to want to be used to mislead prison hearer's keyword, corresponding relation according to keyword and original keyword, generate sub-key, reduce keyword in the original text according to the sub-key of correspondence when extracting original text, the corresponding relation of key is the corresponding sub-key according to sequencing intercepting regular length in total key of keyword.This sender selects the method for keyword can obviously improve the specific aim of misleading, reaches good misleading effect.