Codes and Ciphers · LARRY GILMAN Codes and ciphers are forms of a Hindu text compiled in the a.d. fourth century from manuscripts dating back as far as . Good Privacy (PGP) is downloadable for free from many sites on the Internet. The Playfair cipher or Playfair square or Wheatstone-Playfair cipher is a manual symmetric .. Normally between 4 and 6 answers have to be entered into the grid in code, and the Playfair keyphrase is The Comprehensive History of Secret Communication from Ancient Times to the Internet, Scribner, ISBN Famous codes and ciphers through history and their role in modern encryption . On the commercial internet in a post-Snowden era, it's easy to imagine the . To date, RSA (Rivest, Shamir, Adleman) and AES (Advanced.
Caesar Cipher - Shift Cipher - Decoder, Encoder, Solver, Translator
Encryption keys In order to obfuscate the text more, the concept of changing keys was developed. Using the Caesar Cipher, one could change the ciphertext by simply incrementing the value of the rotation. While the example above is a simple example due to the trivial nature of the Caesar Cipher to begin with, applying more complex keys can rigorously increase the security of ciphertext. Significant Ciphers Throughout history there have been many types of ciphers.
They primarily began as a military tool and militaries are still the heaviest users of cryptography today.
From those military roots, we see that in order to be successful a cipher had to have these attributes. Keep in mind that one error in encryption can render an entire message completely unreadable by the recipient.
Some of the more notable ciphers follow in the next section. Scytale — AD This is a monoalphabetic, symmetrical cipher system. The sender and receiver must both be in possession of a cylinder of wood exactly the same diameter. In effect, this is the key. The sender takes a long narrow piece of fabric and coils it around the scytale. He then writes the message in standard right-to-left format on the fabric. The fabric is then removed from the scytale and looks to be just a long strip of cloth which can be scrunched up and hidden in the smallest of places for transport.
The recipient simply need to wrap the fabric around their matching scytale and the message becomes clear. While this simple cipher would fall very quickly to cryptanalysis, the premise is that only a scytale of exactly the same diameter could decrypt the message.
This is one of the first polyalphabetic ciphers. It is still symmetrical in nature, but it was tough enough to crack that it remained in use for over three centuries.
Polyalphabetic ciphers allow the use of many alphabets during encryption, which greatly increases the key space of the ciphertext.10 Codes and Ciphers
Earlier versions of polyalphabetic ciphers required rigid adherence to the spots at which the alphabet would change. The signal of an alphabet change had to be agreed upon in advance between the sender and receiver, therefore this is still a symmetrical method of encryption. Encrypt and decryption is done by laying out 4 grids. Two grids contain 9 spaces like a tic-tac-toe board, and two grids resemble a large letter X and contain 4 spaces each.
Together, there are 26 spaces to coincide with the 26 letters in the Latin alphabet. The sections are all uniquely identifiable by a combination of the shape of the section and the presence, or absence, of a dot in it. Messages are encrypted by using the section identifier instead of the actual letter.
Decryption is done by laying out the same grid, and transposing back the section identifier to the letter. Playfair cipher — The Playfair cipher uses 26 bi-grams two letters instead of 26 monograms as the encoding key. That vastly increases the key space of the ciphertext and makes frequency analysis very difficult.
Playfair-encoded messages are created by constructing a 5 by 5 grid of letters which is generated by a random short phrase, and then filling in the rest of the grid with non-repeating letters from the alphabet.
That grid forms the key and anyone wishing to decrypt the message must reconstruct this same grid. You can infer from that the recipient must also know the same short phrase used to encrypt the message which is much harder to determine than a simple rotational number.
To accommodate this, the letters I and J are usually used interchangeably. Any two other letters could be used as well, but that information would have to be communicated to the recipient to ensure they decoded the message properly. Once the grid was constructed, users only had to know 4 simple rules to encrypt or decrypt the message. After writing that out, I start writing the alphabet to fill in the rest of the grid. Remember that each letter can only be in the grid once and I and J are interchangeable.
That gives me a Playfair key like the image below.
Caesar Cipher Converter | Online Conversions
The letters in red were omitted because they already appear in the grid. It is not the encrypted text. This resulting grid would be used to encrypt your plaintext. If the keys truly are one timethen ciphertext would be extremely resistant to cryptanalysis. These keys were literally written on pads of paper originally and since each key is only used once, the name One Time Pad stuck.
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In practice, OTP is hard to deploy properly. As a symmetrical system, it requires the sender and all the recipients to have the same OTP book. It also has a significant disadvantage in that a message cannot be longer than the pad in use.
Codes, however, have two great disadvantages. Users can only send messages that can be expressed using the terms defined in the codebook, whereas ciphers can transmit all possible messages. Additionally, all codes are vulnerable to codebook capture. If a codebook is captured, there is no recourse but to distribute new codebooks to all users.
In contrast, the key—algorithm concept makes cipher secrecy dependent on small units of information keys that can be easily altered.
Secure ciphers, however, entail complex calculations. This made the use of complex ciphers impractical before the invention of ciphering machines in the early twentieth century; codes and simple ciphers were the only feasible methods of ciphering.
Yet, a cipher that is simple to implement is proportionately simple to crack, and a cracked cipher can be disastrous. It is better to have to communicate "in the clear"—to send messages that can be easily read by the enemy—than to suppose that one's communications are secret when they are not.
Mary, Queen of Scots — was executed for treason on the basis of deciphered letters that frankly discussed plans for murdering Queen Elizabeth of England ; likewise, simple ciphers used by the Confederacy during the U.
Civil War were easily cracked by Union cryptographers. What is more, even more sophisticated ciphers, such as the Enigma cipher used by Nazi Germany during World War II or implemented today on digital computers, are subject to attack. As soon as any new cipher is invented, someone, somewhere starts attacking it.
The result is that ciphers, like some antibiotics, have limited lifespans, and must be regularly replaced. Throughout much of the ancient world, writing was either completely unknown or was an arcane art accessible only to priests. There was little motive, therefore, to develop coding or ciphering.
Eventually, however, writing came to serve military, personal, and commercial as well as sacred purposes, creating a need for secure communications. To meet this need, ciphers based on scrambling the order of plaintext characters or on substituting other characters for them were developed.
The first recorded use of ciphering was by the Greek general Lysander in the fifth century b. The Kamasutra, a Hindu text compiled in the a. By the first century b. Cryptography fell out of use during the early Middle Agesbut Arab scholars during the heyday of medieval Muslim civilization, the Abbasid caliphate a.
Muslim writers not only ciphered, but invented cryptanalysis, the systematic breaking of ciphers. Ninth-century Arab philosopher Abu Yusuf al-Kindi wrote the earliest known description of the cryptanalytic technique known as frequency analysis, which breaks substitution ciphers by matching ciphertext letters with plaintext letters according to their frequency of use in the language.
In English, for example, the most frequently used letter is E; in an English-language ciphertext produced using a monoalphabetic substitution cipher, therefore, the most frequently used character probably stands for E. During the late Middle Ages and the Renaissancea literate ruling class arose throughout Europeand ciphering regained importance in that part of the world for purposes of intrigue, espionage, and war. English monk and scientist Roger Bacon — wrote a book describing several cryptographic methods; Italian artist Leon Battista Alberti — wrote the first European text on cryptanalysis in Under pressure from cryptanalysis, codes and cipher systems gradually became more complex.
Beginning in the mid-nineteenth century, the importance of coding and ciphering was rapidly amplified by the invention of electronic information technologies: Non-secret commercial codes were developed in conjunction with telegraphy to make messages more compact therefore cheaper ; ciphers were widely used and cracked during the U.
Civil War and the first and second world wars. The cracking of German and Japanese ciphers by Allied cryptographers during World War II was of particular importance, enabling the British and Americans to avoid submarines, intercept ships and aircraft, and otherwise frustrate enemy plans.
Ciphering has since become basic to military and government communications.
Since the s, commercial and personal communications have become increasingly dependent on digital computers, making sophisticated ciphering a practical option for those sectors as well. In the late s, the U. Codes can be generally divided into one-part and two-part codes. In a one-part code, the same codebook is used for encipherment and decipherment. The problem with this system is that some systematic ordering of the code groups and their assigned meanings must be made, or it will be difficult to locate code groups when enciphering or their meanings when deciphering.
A randomly ordered list of words or numbers thousands of terms long is difficult to search except by computer. Thus, code groups tend to be arranged in alphabetic or numerical order in a one-part code, an undesirable property, since an opponent seeking to crack the code can exploit the fact that code groups that are numerically or alphabetically close probably encode words or phrases that are alphabetically close.
Another aspect of Playfair that separates it from four-square and two-square ciphers is the fact that it will never contain a double-letter digram, e. If there are no double letter digrams in the ciphertext and the length of the message is long enough to make this statistically significant, it is very likely that the method of encryption is Playfair.
A good tutorial on reconstructing the key for a Playfair cipher can be found in chapter 7, "Solution to Polygraphic Substitution Systems," of Field Manualproduced by the United States Army.
Codes and Ciphers
Sayers ' mystery novel Have His Carcase. In this story, a Playfair message is demonstrated to be cryptographically weak, as the detective is able to solve for the entire key making only a few guesses as to the formatting of the message in this case, that the message starts with the name of a city and then a date.
Sayers' book includes a detailed description of the mechanics of Playfair encryption, as well as a step-by-step account of manual cryptanalysis. The German Army, Air Force and Police used the Double Playfair system as a medium-grade cipher in WWII, but as they had broken the cipher early in WWI, they adapted it by introducing a second square from which the second letter of each bigram was selected, and dispensed with the keyword, placing the letters in random order.
But with the German fondness for pro forma messages, they were broken at Bletchley Park. Messages were preceded by a sequential number, and numbers were spelled out. Naturally, modern ciphers are not restricted to upper-case, no-punctuation, J-less messages.
Any form of data that can be stored on a computer can be encrypted with a modern cipher. A modern block cipher can be run in a mode similar to that of Playfair, where the same block in Playfair, a pair of letters always encrypts to the same bit of ciphertext: Indeed, many poorly written encryption programs use just this technique, called Electronic Codebook, or ECB.
CFB starts by encrypting something other than the message. This bit at the front of things is called an initialization vector, or IV.