The lore of unbreakable ciphers

With such an obsession around solving puzzles, it’s obvious that unsolved puzzles are by far the most popular, or the ones that capture our imagination. Over the years, there have been many such unsolved puzzles which have caught the imagination of the masses. The notion of invincibility of a cipher has led millions to try their hands at solving them. Despite tremendous advances in the science of ciphers, and using high-end and complex decryption techniques, there are several ciphers still waiting to be translated. In the modern world, where information is power, the field of data encryption has acquired a mighty status. Here we look at some of the famous unbreakable ciphers that have taunted us for years.


From time immemorial, mankind has been obsessed with puzzles. The unquenchable thirst to find answers has become the defining characteristic of our species. One could even go as far as saying that this quest for answers has shaped the advancement we see around us

With such an obsession around solving puzzles, it’s obvious that unsolved puzzles are by far the most popular, or the ones that capture our imagination. Over the years, there have been many such unsolved puzzles which have caught the imagination of the masses. The notion of invincibility of a cipher has led millions to try their hands at solving them. Despite tremendous advances in the science of ciphers, and using high-end and complex decryption techniques, there are several ciphers still waiting to be translated. In the modern world, where information is power, the field of data encryption has acquired a mighty status. Here we look at some of the famous unbreakable ciphers that have taunted us for years.

One-time Pad

One-time pad, sometimes known as the perfect cipher, is an encryption algorithm which combines plaintext with a random key to generate a cipher. Provided that the usage is correct, this type of encryption is the only proven unbreakable encryption. Invented in 1917, the one-time pad was derived from the Vernamcipher, which was named in honor of one of its inventors, Gilbert Vernam. The Vernam cipher used a tape for encryption which was looped after each cycle and reused thereby increasing its vulnerability.

One-time Pad

Owing to its usage by Special Ops teams in World War, intelligence agencies and spies during the Cold War and also in protecting diplomatic communication, the one-time pad gained a reputation for being a simple, yet effective encryption system.


Each character from the plaintext is encrypted by a modular addition with a character from a secret random key of the same length as the plain text, resulting in a cipher text. The ciphertext is impossible to decrypt provided that the key is random, with same or larger length than the plaintext, never reused again and kept secret (obviously). The pad part of the name of this encryption technique comes from the fact that early implementations involved a pad of paper where the top sheet could be torn off and destroyed after use. Subsequently, huge reductions in the size of the pad was possible. KGB went ahead and created pads that fit in the palm of the hand, or even in a walnut shell. In fact, in a very mission impossible-ish turn of events, highly inflammable sheets of nitrocellulose were once used as one-time pads.


Despite being brilliant in theory, there are certain practical issues with the usage of one-time pads. First and foremost, perfect randomness is required in the one-time pads, which can’t exactly be obtained from run of the mill software. High-quality random number generation is difficult to achieve. The random number generation function in most programming languages is not fit for cryptographic use. True randomness is expected to the extent that even if the generating process of a sequence were known up to the last point, it would still be impossible to predict the next event. This simply rules out most running software on computers, which use deterministic processes for random number generation. The next event in a computer is actually pretty predictable, hence they’re unusable.


Radioactive decay is an example of a non-deterministic event. Secure generation and exchange of one-time pad material, which must be as long as the plaintext, is another headache. Most importantly, ensuring its proper disposal to avoid reuse and keeping it secret from any adversary is also an issue.


The pad must be kept secure and has to be as long as (or longer than) the message. Also, you wouldn’t want to send short messages with a one-time pad, and thus a secure long pad can be used to send numerous messages until you run out of that particular pad cipher.


These practical considerations introduce vulnerabilities which hamper real- world application.Nowadays, one-time pads are rarely used. Implementation difficulties have led to the one-time pad being broken time and again, with breaches serious enough to discourage its adoption as a wide-spread information security tool.


Since the pad is too long for any human to remember, you have to carry them in storage media such as pen drives, DVDs, etc. This is cumbersome, especially when you compare it to modern public key cryptosystems. The risk of compromise during the transportation of the pad, such as someone stealing, copying and returning the pad also cannot be ignored. The effort needed to manage one-time pads for large networks is also a scalability issue.A famous example of a slip-up using one-time pads: The Soviet intelligence decided to reuse older one-time pads (after many years), as someone assumed this would be pretty secure. This was used to communicate with undercover agents in the UK. British Intelligence picked up on these messages, and noticed a pattern that matched messages they had intercepted many years ago. Needless to say, a large number of encrypted communications were eventually compromised, and there’s no doubt a few people found a new permanent home in Siberia, if not worse.


Despite the drawbacks, the one-time pad is still the preferred encryption technique when the encryption work is done by hand. This was the major reason it was so popular in the pre-computer era.

The Voynich Manuscript

Considered to be the world’s most mysterious manuscript, the Voynich Manuscript is a work which dates back to the 15th century. The manuscript, which is heavily illustrated with drawings of astronomical events and botany, was bought by a books dealer called Wilfrid M. Voynich, who later took it to the United States of America to have its text deciphered. Almost 100 years later, we still have no clue as to what the text in this manuscript stands for.

The mysterious Voynich Manuscript

The fluency of writing observed in the manuscript indicates that the symbols were not enciphered. There is no delay between characters which would be expected in a written encoded text. However, this could also have been achieved by copying prepared coded text from another source. Further, statistical analysis of the text reveals patterns close to that of natural languages. On the other hand, the manuscript’s language is not very different from any other European language in several aspects.


Words comprised of more than ten characters are rare and so are words having one or two characters. The distribution of characters is striking as well, because some consistently appear at the beginning, middle or end of the word. The text seems to be more repetitive than typical European languages though, and there are times the same word appears more than twice, consecutively.


Some have suspected Voynich of forging the manuscript himself. As an antique book dealer, he had the requisite knowledge, and a lost book would have been worth a fortune. However, carbon dating of the manuscript put an end to that theory.


The idea that this manuscript is a hoax is supported by the strange features of the text in the manuscript, the suspicious nature of its contents, and lack of any historical proof. It was asserted that the reason no one was able to extract the meaning from this manuscript could possibly be that none existed in the first place. The argument against this suggests that the manuscript is too sophisticated to be a hoax. Hoaxes of that period generally tended to be crude. A simple forgery need not be as intricate as this manuscript, which has many fine touches – some of which are visible only by using more modern tools.


This manuscript has been the centre of attention for many cryptographers across the world, including code breakers from both World War I and II. As of now, no one has been able to solve it and it has become an important part of the history of cryptology. The manuscript was donated to the Yale University where it is known as MS 408.

The Zodiac Killer

The Zodiac Killer was a serial killer who operated in California, USA in the late 1960s and early 1970s. It is one of the greatest unsolved crimes to date. Four men and three women between the ages of 16 and 29 were murdered. The police investigated over 2,500 potential suspects, but the forensic techniques of the day were not advanced enough to conclusively convict anyone. The killer identified himself as the “Zodiac” in a series of taunting letters which he sent to the local press. These letters included four cryptograms or ciphers. Until now, only one of the four has been solved. In 1969, one of the four cryptograms was cracked by Donald Harden. It contained a misspelled message in which the killer claimed that he was collecting slaves for the afterlife.

Zodiac killer left us all puzzled

The Zodiac Killer’s ‘Three part cipher’ consisted of three different parts being mailed to three different newspapers in mid 1969. The cover letters were similar and included confessions to earlier killings and threats to kill even more people if his ciphers were not published on the front page of respective newspapers. Further, they also stated that the ciphers contained his identity.


Another one of Zodiac’s ciphers was sent to the San Francisco chronicle. It was a 148-character cipher, written at the top of a letter. The cipher was followed by Zodiac killer’s crosshair symbol.

Edgar Allan Poe

Edgar Allan Poe was an American author and cryptography enthusiast. Considered the inventor of detective fiction genre, he pursued activities in the field of cryptography as well. He invited submissions of ciphers and puzzles through advertisements in newspapers and then proceeded to solve them. He went on to publish an essay on cryptography called “A Few Words on Secret Writing”. His novels incorporated ciphers and encryption as a part of the story (Yes, just like Dan Brown). His eventual success in the field of cryptography can be attributed less to his knowledge of the subject and more to his knowledge of the magazine and the newspaper culture. Largely ignorant about the field of cryptography, the general public was awestruck by Poe’s method of solving a simple substitution cryptogram.

Edgar Allan Poe loved cryptography

Poe created a sensation through his articles and ended up popularizing ciphers in print media, a trend which continues to this day. Many future notable figures in cryptography were heavily inspired and influenced by Poe’s work. Poe released two ciphers as a challenge for his readers. They remained unsolved for a long time, till the first of these was cracked in 1992. A contest was established for the solution of the second cipher which was eventually cracked in 2000. There has been a revival of interest in his work due to the recent movie “The Raven”.

The Cyrillic Projector

This is a sculpture in the University of North Carolina which was created by Jim Sanborn, an American artist, in the 1990s. It is an encrypted sculpture and is one of three puzzle sculptures made by Sanborn. The text on the sculpture is in Russian. It is essentially a riddle wrapped on a cylinder. One half of the cylinder is a 16th century decoding chart. The chart can be used to decode the other half of the cylinder, which contains a coded text describing the dangers of suppression of intellectual and artistic freedom.

This was finally decrypted in 2003 by Elonka Dunin. The sculpture consists of two messages. One is Russian text that shows the usage of psychological control to develop and maintain sources of information. The second message pertains to the scientist Sakharov who was a Nobel Peace Prize winner as well as a Soviet dissident. The message finds its origins in classified KGB files.

The Oak Island treasure

Oak Island is a 140 acre privately owned island in Canada. It is noted as the location of the“Money Pit” and has been the site of a treasure hunt for over 200 years. Artifacts have reportedly been found as deep as 30 meters, but all such excavations ended in the collapse and flooding of the pit. In 1975, after observing “strange lights”, a few teenagers discovered a depression on the south eastern end of the island. Upon digging up the depressed area, a layer of flagstones and markings from a pick were discovered. One of the larger stones had an inscription of symbols, and several attempts were made to decipher it. One of the most famous translations is “Forty feet below, two million pounds lie buried.” The pit subsequently flooded.

It has been argued that there is no treasure in the pit, and it is but a natural phenomenon. Such suggestions alleging the pit to be a natural sinkhole date back to early 1900s. There are numerous sinkholes on the mainland near the island, together with underground caves. Appearance of man-made pits has been attributed to the texture of sinkholes. The filling would be softer than surrounding ground leading to the impression that it were dug up before. The appearance of rotten logs can be attributed to trees falling. Another pit of similar description had been discovered in the surrounding area which lends credence to the natural phenomena theory.


Kryptos is an encrypted sculpture by Jim Sanborn, who is also the creator of the Cyrillic Projector, located on the grounds of Central Intelligence in Langley, Virginia. The sculpture has been made with four copper plates and other elements such as granite, quartz and wood. There has been speculation about the encrypted message it bears. The name comes from the Greek meaning ‘hidden’ which signifies the theme of the sculpture, intelligence gathering. The main sculpture consists of four separate enigmatic messages. Three of them have since been cracked. The sculpture was installed in 1990. The first three parts were solved by an NSA analyst in 1992. Notably, a CIA analyst was able to crack the code using pencil and paper techniques. The fourth part is yet to be solved and is one of the most notoriously famous unsolved ciphers in the world. Since 2003, an active Yahoo group coordinates the work of over 2,000 members to decrypt the final sculpture.

Hint for enthusiastic readers: The answer to the first part contains the clue to the final part.

Vigenère cipher

The main problem with simple substitution ciphers is that they are susceptible to frequency analysis. Provided we have a sufficiently large cipher text it can be broken by comparing the frequency of its letters it to that of letters in different languages. The aim for cryptographers was therefore to make encryption techniques that were immune to frequency analysis.

A common approach is to suppress the frequency data using more than one alphabet to encrypt the data. The Vigenère cipher is one such method which is a simple form of polyalphabetic substitutions. The method was originally developed in the 16th century but was later misattributed to Blaise de Vigenère and is now known as the Vigenère cipher. The cipher is very well known because it is easy to understand and implement and appears unbreakable to beginners. This is where it acquired its reputation of being unbreakable. Spurred on by the myth, a number of people have tried to implement the encryption scheme of this cipher, only to have them broken. Charles Babbage was the first person to have broken a variant of this cipher. The main weakness of this cipher is the repeating nature of its key. If the key’s length can be correctly guessed, then the ciphertext essentially becomes a combination of interwoven ciphers, which individually are easily broken. Efforts were made to improve this cipher, which led to the development of the one-time pad.

Indus valley script

The term Indus valley script refers to the strings of symbols associated with the Indus valley civilization in use during the middle of the second millennium BC. It is not generally accepted that this script is used to record this language. The first publication of Harrapan seals dates back to the 1870s. A number of objects bearing symbols from the Indus valley script have been discovered in the past few years. It was believed that this script is related to the Brahmi script. After multiple attempts to decipher the script, there is still no success in sight and it is still listed as undeciphered. The language for which this script was used has also not been identified yet. Over the years, a number of solutions have been proposed, but none have been widely accepted. One of the biggest challenges in the deciphering process is that no language has been identified, although some words from the Rigveda are sometimes used for comparison. The fact that the average length of the inscriptions is quite small only adds to the complexity. Further, no bilingual texts have been found. The topic is extremely popular among amateur researchers and various decipherment claims have been seen, though none of them have found any recognition.

Beale ciphers

The Beale ciphers are three ciphers which state the location of a buried treasure worth about $63 million in today’s money. Two of the ciphers describe (unessential) details such as the contents of the treasure and the names of the people in the family of the original treasure owner. The story originates from an 1885 pamphlet that claimed a buried treasure was hidden in a secret location in Virginia in 1820. All three cipher texts were published in the pamphlet. The cipher detailing the contents of the treasure was deciphered using the Declaration of Independence of the United States as the key. The other two ciphers remain unsolved. Later on there has been considerable debate on whether the cipher texts are real or hoax. It has been alleged that there is evidence based on the kind of words used, proving that the document could not have been written at the time it says it was.

Dorabella Cipher

This cipher is an encrypted letter written by Edward Elgar to Miss Dora Penny in the late 19th century.Edward Elgar was a music teacher, and Dora was almost seventeen years his junior. The letter could not be decrypted. The cipher consists of 87 characters, is over three lines long and seems to be made up from 24 symbols that consists of up to three semi circles oriented in eight directions. The symbol frequency is similar to that of

English, but attempts to decipher it as a simple substitution cipher have not yielded any results. Some theories regarding the solution presume that the solution is not text but a melody and the 8 different positions indicate notes of the scale. In commensuration of Edward Elgar’s 150th birth anniversary, the Elgar society heavily

advertised the cipher.

Linear A

Linear is one of the two writing systems used in ancient Crete along with Linear B. Primarily, Linear A was used a script for religious purposes. Linear A is generally understood to be used between 1800 to 1450 BC. It was discovered by Sir Arthur Evans in 1900 (AD). A large number of clay tablets inscribed with mysterious symbols were found. Sir Evans believed he had discovered the mythical palace of King Minos and the Minotaur’s labyrinth, and christened the inscriptions and languages they represented as ‘Minoan’. Evans spent his remaining life trying to decipher the inscriptions with limited success. Three writing systems were used, including somekind of hieroglyphic script, Linear A and Linear B.Out of these three only Linear B has been deciphered, the rest are yet to be understood. It is believed that the hieroglyphic script led to Linear B which led to Linear A, though the relationship is unclear. Linear B was largely deciphered in the 1950s. Although Linear A and Linear B share a lot of symbols, Linear A is still a mystery waiting to be solved.

Phaistos Disc

The Phaistos Disc is a disc of clay obtained from Crete, Greece from about 2000 BC. It is covered on both sides by a spiral of stamped symbols. Its purpose, meaning and where it was manufactured continues to be a mystery making it one of the most famous archaeological ciphers. The disc was discovered by Italian Luigi Pernier in 1908. It features a number of tokens and unique signs presumably made by pressing of discs into the soft clay. Numerous attempts have been made to crack the cipher. Despite existence of uncertainty on whether there is script behind the signs, most decipherments assume this. Attempts at deciphering the code seem unlikely to succeed without further examples of signs. It is believed that there is not enough material available for a meaningful analysis. It is also speculated that this disc could be used to decipher Linear A.

Rongorongo Script of Easter Island

Rongorongo is the system of writing discovered on Easter Island. The people of Easter Island were probably inspired to invent the Rongorongo script after seeing the writing used by the Spanish. Rongorongo was used till the 1860s after which the knowledge was lost. With the advent of missionaries, attempts were made to understand the language. Numerous attempts have been made at decipherment; none have been successful so far. Some information has been identified as their perception of a calendar, but the majority remains unread. If Rongorongo does indeed prove to be writing, it will be one of the few independent inventions of writing in the history. Assuming Rongorongo is truly writing, there are three serious challenges to cracking the cipher including the small appearances of text, the language on which it is based and no context whatsoever in which to interpret them.


Bulambod is a type of encryption software which is freely available online. It’s a cipher algorithm which is allegedly not based on existing algorithms. It was not invented recently, but was started in the 1990s with an aim to make an unbreakable cipher. Its main strength is the length of the password it allows. It further allows the user a possibility to use a number system of his own choice for encryption. While there are a number of ciphers that have not yet been deciphered, their number is declining steadily. Modern computation techniques and improvement in algorithms, are equipping us with better tools for decryption. Of course, better computing machines also mean that we can get better at encryption techniques as well, and it seems for now that the balance is holding up quite well.


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