GNOSIS 4/2011
|
The coded message travels with bacteria |
|
Antonio TETI |
The concept of steganography The study of techniques and methods to make communications confidential between two interlocutors has always represented, since the times of the Greek historian, Herodotus (1) ,the greatest torment for all the important supporters of the secrecy of transmitted information. It was, in fact, this Greek historian – considered by many as the “Father of history” (because of his famous work entitled “Storie”, in which he narrates the events that led Greece into war against the Persian Empire) – who recounts a curious episode in which we see the first attempt of masked transmission of a message. Historically, the episode takes place during the period of the same war between Greece and Persia, and refers to the need of a noble Persian, who is obsesses by the search for a system that can secretly transmit a message to one of his allies. The content of the message required a level of absolute secrecy and it was essential that no-one should have access to it, but the legitimate recipient. Naturally, the possibility of entrusting the manuscript to a courier presented considerable risks. The first being the facility of access to the information in the case where the courier fell into the hands of the enemy, the second was the trustworthiness of the same courier, who could have read the content of the message to then reveal it to the enemy. At this point, the noble Persian had a brilliant idea: to shave the head of the courier so that the message could be tattooed on the skin of the cranium; once the hair had re-grown, the messenger was sent to the destination, with the only instruction to re-shave the courier’s head upon delivery of the message. The Greeks had always used another form of steganography which was based on the use of wooden tablets. The text was etched on wax-covered tablets which were subsequently totally recovered with a second stratum of wax, to make the object appear new. However, the first real system of masking a message must be attributed to Caius Julius Caesar. It was a rudimentary system, but for those times, appeared revolutionary. The Julius Caesar cipher was based very simply on the translation of a certain number of letters of the alphabet (shifting algorithm) For example, starting from: and assuming a rule which is based on the translation of three letters, the result is: Naturally, it is essential to establish a priori what the algorithm of translation to adopt must be, which can be based also on the alternation of sequences of substitutions of numbers and letters (first of three and then of four, or, the first letter is made to translate to three and the second to four, etc.). Also in ancient China, techniques based on the use of the body of the messenger were developed. Narrow strips of cloth (mainly silk) were cut: each strip was then rolled with wax into small balls. These were swallowed by the unfortunate courier, who had the task of transporting them to destination. Once reaching the goal, the extraction of these cloth marbles, if not accomplished in a natural way, could result fatal for the unlucky traveller. On the other hand, in those times, the value of a message could well go beyond the life of some insignificant servant …. Starting from the beginning of the 8th Century, also the Arab civilization contributed to the development of particular techniques of steganography. It seems that in a book written by an Arab mathematician, a solution was found to understand messages hidden within certain cryptograms written in Greek by officials of the Byzantine Empire. Another Arab scholar cites the names of animals, fruits and flowers to identify the letters of the alphabet. During the course of the subsequent centuries, a variety of methods and sophisticated alchemies were used to mask the transmission of secret messages, but only in 1518, the first real manual dedicated to concealing the meaning of a message was realized.This we owe to Johannes Trithemius (Trittenheim, 1st February 1462 - Würzburg, 13th December 1516), German Abbot and intellectual, and passionate enthusiast for all things esoteric, who realized an imposing work of six volumes, which was published some years after his death. The first of theses contains 384 columns of Latin words, two columns for each page and each word representing a letter of the alphabet (Figura 1).  Figura 1 - Una pagina del testo The principle is based on the substitution of the words with the letters that compose the secret message. Therefore, substituting these words in the place of the letters which compose a secret message, passages are obtained which appear as simple prayers (for example, by encrypting the letters of the word ‘abbot’ (abate), the following phrase in Latin is obtained: “Deus clementissimus regens aevum infinivet”). In 1550, Girolamo Cardano, the flamboyant and greatly talented Italian mathematician, developed a system of masking of the message by grid, which took the name of the Grid of Cardano. It was based on the use of an ordinary sheet of paper (grid) on which slots were appropriately cut out, through which it was possible to insert a message, superimposing it on an underlying sheet. After the insertion of the message, the grid was removed and the portion of the message was completed with the aim of giving it a precise sense and making it appear a normal message (Figure 2-3).  Figura 2 - Testo di un normale messaggio  Figura 3 - Testo visibile con l'apposizione della griglia di Cardano The grids, which can be of paper or metal, are positioned arbitrarily on the sheet and do not follow any precise rule. Also for this reason, the Cardano system became identified as a cipher grid. Naturally, it is indispensable that both the sender and the recipient possess the same personalized grid. Nevertheless, the episode narrated by Herodotus remains the first true model of steganography, precisely because it adopted a superior technique, which aimed at the total concealment of a communication between two interlocutors. It is necessary to underline that steganography is not to be confused with cryptography, which concerns the hiding of the content of a message and not the message itself. Thus, steganography, as a method of secrecy can be considered safer and more reliable. In recent year, the study of these techniques has returned to arouse the interest of many experts, many of whom work in the Defence sector, tenaciously convinced that the future of the confidential information will be based on this single system of the masking of the message. Furthermore, it has also been demonstrated that the sole use of cryptography has proved unsatisfactory in many situations. Many Intelligence Services of different Countries have suffered thefts of data and violations of access specifically relating to the demolition of complex algorithms of encryption held to be, until that time, indecipherable. In addition the encryption of the data nevertheless arouses suspicion. The very fact that it is known that two interlocutors use encryption systems, automatically generates an aura of suspicion and overwhelming interest for anyone wanting to reveal its contents. Added to this is the fact that the multiple restrictions and controls imposed by many Governments on the systems of cryptography have contributed to give a further drive to the development of steganography. Also during the Second World War, the techniques of steganography were experimented, among which the most famous was that of the zero digits. Used by both the allies and the Germans, particularly for radio transmission, this technique was based on the insertion of a message hidden within another message text. Also in this case, the message was composed in such a way as to appear quite ordinary, but using a sequence of extrapolation of characters, it was possible to obtain quite a different message. The following indicated example (Figure 4-5-6), is attributable to a text which was actually sent by a German spy. The message is compiled in such a manner as to obtain – thanks to the extrapolation of the second letter of every paragraph – a completely different communication.  Figura 4 - Messaggio in chiaro  Figura 5 - Estrapolazione della seconda lettera di ogni capoverso Even if, in reality, there is one “r” too many in the message, it is clear that the system of those times, offered a series of rather high and complicated combinations and schemes of extrapolation, which conferred considerable reliability on the technique of the zero digits.  Figura 6 - Messaggio ricavato dalla estrapolazione During World War II, other techniques of masking secret messages were experimented, such as the use of invisible ink. Substances which normally leave no trace on any sheet of paper, but become completely visible when the paper is exposed to a source of heat. Common substances were used, such as lemon juice, vinegar and milk, but also chemical substances such as cobalt ink, which can be made visible only by particular chemical reagents. With the passage of time, technological evolution began to produce important results in many sectors, including that of the camouflage of the images. Invented by the Germans during the last War, the technique of the microdots marks a substantial step ahead in steganography, to the point that Edgar J. Hoover, the very powerful director of the Federal Bureau of Investigation (FBI), defined it quite bluntly as “the masterpiece of the enemy in espionage”. It was only, thanks to the interception, in 1941, of a German agent who transported a magazine in which was imprinted a microphotograph, that the allies discovered this new technique of masking. It is based on the use of very tiny photographs (a typewritten dot) which, once enlarged, become good quality images, and their camouflage could be made possible by their insertion into different photos of no significance (Figura 7).  Figura 7 - Esempio di tecnica di micropunti fotografici Steganographic models As we have understood, these techniques are based on the existence of two messages: the first that acts as message masking and has the job of hiding (masking) the second message (the secret message), which contains the confidential information. The fundamental assumption is that the secret message is not visible, interceptable or perceptible in any way, by anyone who is not informed in advance. However, there are different approaches which can be traced to two types of application. Depending on the source of the “container” file, we can distinguish the software of injective steganography and that of generative steganography. The first category is the more known and diffused one. Essentially, the software that belongs to this family allows the injection of the secret message into an already existing message. Modifying it in such a way as to render the two messages inseparable (Figura 8).In this case the secret message is made totally invisible, since it is diluted within the normal message.  Figura 8 - Schema di steganografia iniettiva The generative steganography is founded on the concept of the generation of the container message starting from the secret message. In essence, it is the secret message that creates its container, which will have the job of hiding it in the best way (Figura 9).  Figura 9 - Schema di steganografia generativa SAccording to a different system of classification, the more practice oriented steganographic techniques can be divided into three classes: substitutive steganography, selective steganography and constructive steganography. Substitutive steganography is, without doubt, the more diffused and used technique, and when systems based on this methodology are cited, reference is always made to this one. It is based on the concept of “noise”. Starting from the thesis that identifies noise as a typical disturbance of channels of communication (telephone lines, radio transmission etc.,) this “nuisance” can be substituted by a signal (the secret message) which, appropriately modified, would assume the role of the typical noise of data transmission. This interference, considered normal, would not give rise to any suspicion in the data/voice transmission sessions. In digital transmission, the work of modification of the noise results in the replacement of the less significant bits of the message (file), with the bits that represent the secret message. Although it may appear complex, in reality, the concept is very simple and is based specifically on the architecture of the digital transmission: each character can be expressed by a sequence of bits (0 and 1) that combine to form a byte (composed of 8 bits), therefore, without entering into explanations which might appear excessively complicated, it is sufficient to add the less significant bits (the secret message) to hide confidential information within the others considered to be significant. Substitutive steganography is a very difficult process to discover, unless one goes through a particular and laborious analysis of the transmitted file. Furthermore, this technique can be used for any type of transmitted file (images, sounds, digital video). Selective steganography has a purely conceptual importance and, as far as its uses are concerned, it seems it is almost unused. It is based on the idea of the conduction of attempts, that is, repeating the same measure until the result satisfies a specific condition. In order to simplify the concept, let us suppose that the process of masking is based on the manipulation of an image and it is submitted to acquisition by a scanner. If the result does not produce a certain kind of information (set of data), then the process is repeated. It is clear that this technique is too costly, especially in terms of time, and if we consider the minimal amount of information which can be hidden, it does not seem very usable. Constructive steganography is a very similar technique to the substitutive one, but differs from it because, in the construction phase of the container file, the model of noise is also taken into consideration. In substance, attempts are made to replace the noise of the medium utilized, with the secret message, maintaining the characteristics of the initial noise unaltered. Even if, on the surface, it could appear to be the most efficient system, it has more than a few weak points. For example, the complexity of the model which, if not properly done, could be the element of discovery of the type of masking of the secret message. The future of the encryption of information: Steganography by Printed Arrays of Microbes Spam is a very well known term in the cyberspace. Known also as spamming, it identifies that intrusive and annoying form of undesired publicity which affects practically all those who frequent the cyberspace and use the e-mail. The origin of the term ‘spam’, according to Wikipedia, is connected to a comedy sketch of the Monty Python’s Flying Circus. The scene is a place where tinned meat is served, better known by the name of Spam. The most characteristic aspect of the sketch lies in the insistence of the waitress in suggesting to all the clients, the dishes in which Spam is present (eggs and Spam, eggs, bacon and Spam, sausages and Spam etc.,) and in the reluctance of the clients to order the food obsessively proposed to them by the waitress. Probably, the choice of the term ‘spam’ in identifying the annoying phenomenon of the publicity messages on the Net, is attributable to that same sensation of displeasure which those clients felt who were forcibly proposed the tinned meat. However, in these months, we could be seeing a revision of the meaning of this term. Indeed, the term spam could even assume a positive significance in the collective imagination, and this would be made possible thanks to an extraordinary experiment conducted in the biotechnological sector: the possibility of using bacteria modified in laboratory to hide secret messages. The news came out at the end of September 2011 and was published in a prestigious scientific review, PNAS (Proceedings of the National Academy of Sciences) by a group of researchers headed by David Walt, a chemist and researcher of the Tufts University of Medford, Massachusetts. The acronym SPAM is, in this case, Steganography by Printed Arrays of Microbes, and refers to a revolutionary technique which allows, thanks to appropriate laboratory modifications, the writing and deciphering of a code using the Escherichia coli bacterium (2) (ricordate il batterio killer che si annidava nella frutta e nella verdura?). (remember the killer bacterium that lurked in fruit and vegetables?) Although this multirole bacterium, known better by the initials E.coli, habitually dwells in the intestines and has a fundamental role in the digestive process, it can also provoke terrible and even fatal sicknesses (urinary tract infections, meningitis, peritonitis, septicemia and pneumonia). Nevertheless, its versatility at a functional level (which seems to be its greatest feature) could, today, be attributed with the role of the first bacterium engaged as an operative agent in the Intelligence Services. At this point, let us try to better understand the type of experimentation conducted by David Walt. Basically, a protein is inserted in these bacteria, which is able to emit a fluorescent light available in seven different colours (GFPuv, AmCyan, ZsGreen, ZsYellow, mOrange, tdTomato and mCherry). Then the bacteria are positioned on a sheet of nitrocellulose in groups of two (according to the schema seen in Fig. 10).Figura 10).  Figura 10 - Tabella di attribuzione colori-batteri Fonte:http://www.pnas.org/ As is easily inferred from the graph, two batteries are needed to represent the letter “h”, one green and one yellow; two other batteries will be needed to represent letter “s”, but one green and one red. As is shown by Fig. 11, Figura 11, the group of researchers headed by Walt, utilizing 144 coloured dots which correspond to 72 characters (including spaces), was able to compose the message “this is a bioencoded message from the walt lab at tufts university 2011”.  Figura 11 - Tabella di conversione colori-caratteri Fonte:www.pnas.org/ This experiment throws open the doors to a multiplicity of scenarios which can lead down countless paths and, in many ways, unknown ones. For example, in the case of different bacterial strains being used, it is possible to make the single bacterium produce fluorescent proteins to different timing. This would increase exponentially the levels of encoding of the bacteria themselves and it would be possible, thanks to the timing of the bacteria signals, to create a periodic forwarding system of the messages. Another variable that could provide a springboard in the process of the construction of the biological message is the use of antibiotics. As is well-known, antibiotics are substances of natural origin produced by a microorganism which is able to eliminate another (it is no coincidence that the word ‘antibiotic’ derives from the Greek “against life”). However, in the common use of the term, it identifies a pharmaceutical product able to counteract the diffusion of bacteria. Being able to exercise a direct conditioning on the bacterium, an antibiotic can be easily utilized also to modify certain characteristics. In this case, an appropriately modified antibiotic is able to act on the capacity of the bacterium to produce the fluorescent colour. Let us make an example: suppose we utilize bacteria that are able to resist the rifampicin antibiotic. The moment we insert the aforementioned antibiotic on the nitrocellulose sheet, the bacteria, also in the presence of rifampicin, would remain alive and would produce their fluorescent colour, encoding a specific message. If, instead, in the same bacteria also the genes for another fluorescent colour are inserted, coupled to the resistance of another antibiotic (let’s say erythromycin), the code reading would change: in the presence of rifampicin, only the bacteria able to resist them would remain alive, but would produce the colour associated to the resistance to erythromycin. In short, through the use of antibiotics, it would be possible to keep alive certain bacteria (and therefore the messages of interest) and destroy others (considered unimportant or already read), but it would also be possible to modify the colours produced, altering, as a consequence the content of the message. From the operative point of view, the function of the transmission of the messages would come about in the following way: the messages are cultivated on agar plates (3) and subsequently transferred onto a thin pellicle which can also be sent by post to the recipient. The pellicle appears blank to the recipient, but the message is revealed when the bacteria is transferred onto an appropriate culture medium. Thus, the latter acts as the secret key for the deciphering of the message. For example, if some bacteria are treated with a specific antibiotic, the secret message can be read only with a particular chemical substance. In the case where an unsuitable substance is used, the message could result as an insignificant text or could even be destroyed. Walt himself states that the modifications of the genetic traits could lead to thousands of possible encryption keys of the message. Further studies are focused on other bacteria such as the Bacillus subtilis, a non-dangerous microorganism, but has demonstrated to be particularly susceptible to genetic manipulation and is widely used as a model organism for many laboratory studies. It is not surprising then that this project of cultivation of bacteria messengers was financed by the U.S.A. Defence Advanced Research Projects Agency (DARPA) which, already for some year, has launched a challenge to the chemical laboratories of the Unites States to discover a system that would allow the transmission of encoded information by utilizing chemical signals. It was not then by chance that in 2010, Craig Venter, scientist of the homonymic Institute Venter, demonstrated how it was possible to insert secret messages under the form of amino acids incorporated in the first artificial bacterial genome (4) In other words, secret messages hidden in the DNA. But Doctor Walt states that his system is much more reliable and, above all, simpler to implement. “If one is trying to send a message and does not have a DNA synthesizer to hand, the problem can be solved simply through the transport of bacteria”, Walt asserts and goes on: “Using my system, it is possible to speculate on a myriad usable applications for espionage”. Probably, the greatest feature of this extraordinary system of secret communication lies in the very simplicity of its construction, which also represents the greatest advantage for its utilization, i.e. the enormous difficulty in identifying and deciphering the biological message. The selection markers can be numerous and can assume different meanings and, moreover, it cannot be forgotten that to identify an “encrypted” biological message necessitates complex laboratories and equipment, which are costly and not simple to prepare. On the other hand, the bacteria, which constitute the vehicle of transposition of the secret message are particularly sensitive to environmental modifications (temperature, adverse climatic conditions, viruses, medicines etc.,) therefore, their failed survival would lead to the loss of the transmitted message. Another aspect, not to be underestimated, is the quantity of information which would be conveyed by means of the bacteria. Disposing of an information density far below that of the DNA, the messages contained in the bacteria could reach 500-1000 symbols, which would be, as Walt states: “…sufficient for a mission update, but probably insufficient to smuggle the secrets of a foreign Country”. Similar doubts have been raised by other eminent scientists of the sector. “It is a remarkable experiment, but I am very doubtful about its practical relevance”, explains Dominik Heider, researcher of the German Duisbug-Essen University, specialized in the applications of encryption of messages that utilize the DNA. Furthermore, he poses the question of the restrictions which many Countries impose on the transmission by post of genetically modified bacteria. In any event, Science has made a further step ahead, offering man another prodigious instrument for the masking of messages. That biotechnology represents one of the leading sectors of the third millennium has been clear for some time, but the discoveries and innovations attributable to it open possibilities and scenarios for man which are difficult to predict. We can only wait for the evolution of the future events to understand what the use of this extraordinary experimentation will be, in the hope that it does not prove harmful like other discoveries of the past, which would have been useful had they not been used in a devastating way. Per approfondimenti l’autore suggerisce la consultazione di.. - http://www.nature.com/news/2011/110926/full/news.2011.557.html - http://www.theepochtimes.com/n2/science/living-invisible-ink-bacteria-engineered-to-encrypt-messages-62182.htm - http://www.pnas.org/content/early/2011/09/19/1109554108 - http://now.tufts.edu/articles/bug-code - http://io9.com/5845233/secret-agents-of-the-future-could-use-bacteria-to-send-hidden-messages - http://www.tuftsdaily.com/tufts-team-uses-bacteria-to-send-secret-messages-1.2656049
| |
|
(1) Herodotus – Halicarnassus, (484 BC – 425 BC Thurii) was an historian of Ancient Greece, famous for his descriptions of places and people known to him in his numerous voyages. In particular, he wrote about the Persian invasion of Greece, in the work Storie (Historiai). He is considered to be “The Father of History” because in his single work entitled Storie (which, in Greek means enquiry or research) he tries to identify the causes which led to the war between the united poleis of Greece and the Persian Empire, putting it in an historical perspective and using investigation and distrusting the accounts of his predecessors. Source Wikipedia.
(2) Escherichia coli (abbreviated E.coli. It is the best known species of the Escherichia genre: in its inside at least 171 serotypes can be distinguished, characterized by different combinations of the antigens O, H, K, F, E. It is one of the principal species of bacteria which live in the lower part of the intestines of warm blooded animals, (birds, mammals including humans) and are necessary to the correct digestion of food. Its presence in bodies of water signals the presence of defecation conditions (it is the principal indication of faecal contamination, together with the enterococci). The name derives from its discoverer, the German-Austrian Theodor Escherich. It belongs to the enterobacterial group and is commonly used as a model organism of bacteria in general. Source Wikipedia. (3) Agar. It is a polysaccharide used as a natural gelling agent and it is obtained from red algae belonging to different genres (among which Gelidium, Gracilaria, Gelidiella, Pterocladia, and Sphaerococcus. The Agar cannot be digested by the enzymes present in the greater part of organisms, including bacteria and it is for this reason that it is used in microbiology to solidify the culture media for these organisms. (4) Genome. In the field of classic genetics, the term genome identifies the genetic inheritance and that is the set of chromosomes contained in each cell of an organism. In the molecular biology sector, the genome is indicated as the inheritable information of an organism (contained in the DNA). |