A report on Cryptography

Lorenz cipher machine, used in World War II to encrypt communications of the German High Command
Alphabet shift ciphers are believed to have been used by Julius Caesar over 2,000 years ago. This is an example with k = 3. In other words, the letters in the alphabet are shifted three in one direction to encrypt and three in the other direction to decrypt.
Reconstructed ancient Greek scytale, an early cipher device
First page of a book by Al-Kindi which discusses encryption of messages
16th-century book-shaped French cipher machine, with arms of Henri II of France
Enciphered letter from Gabriel de Luetz d'Aramon, French Ambassador to the Ottoman Empire, after 1546, with partial decipherment
Symmetric-key cryptography, where a single key is used for encryption and decryption
One round (out of 8.5) of the IDEA cipher, used in most versions of PGP and OpenPGP compatible software for time-efficient encryption of messages
Public-key cryptography, where different keys are used for encryption and decryption.
Whitfield Diffie and Martin Hellman, authors of the first published paper on public-key cryptography.
In this example the message is only signed and not encrypted.
1) Alice signs a message with her private key.
2) Bob can verify that Alice sent the message and that the message has not been modified.
Variants of the Enigma machine, used by Germany's military and civil authorities from the late 1920s through World War II, implemented a complex electro-mechanical polyalphabetic cipher. Breaking and reading of the Enigma cipher at Poland's Cipher Bureau, for 7 years before the war, and subsequent decryption at Bletchley Park, was important to Allied victory.
Poznań monument (center) to Polish cryptanalysts whose breaking of Germany's Enigma machine ciphers, beginning in 1932, altered the course of World War II
NSA headquarters in Fort Meade, Maryland

Practice and study of techniques for secure communication in the presence of adversarial behavior.

- Cryptography
Lorenz cipher machine, used in World War II to encrypt communications of the German High Command

130 related topics with Alpha

Overall

Close-up of the rotors in a cipher machine

Cryptanalysis

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Cryptanalysis (from the Greek kryptós, "hidden", and analýein, "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems.

Cryptanalysis (from the Greek kryptós, "hidden", and analýein, "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems.

Close-up of the rotors in a cipher machine
First page of Al-Kindi's 9th century Manuscript on Deciphering Cryptographic Messages
The decrypted Zimmermann Telegram.
The Bombe replicated the action of several Enigma machines wired together. Each of the rapidly rotating drums, pictured above in a Bletchley Park museum mockup, simulated the action of an Enigma rotor.

Cryptanalysis is used to breach cryptographic security systems and gain access to the contents of encrypted messages, even if the cryptographic key is unknown.

An unpredictable (typically large and random) number is used to begin generation of an acceptable pair of keys suitable for use by an asymmetric key algorithm.

Public-key cryptography

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Cryptographic system that uses pairs of keys.

Cryptographic system that uses pairs of keys.

An unpredictable (typically large and random) number is used to begin generation of an acceptable pair of keys suitable for use by an asymmetric key algorithm.
In an asymmetric key encryption scheme, anyone can encrypt messages using a public key, but only the holder of the paired private key can decrypt such a message. The security of the system depends on the secrecy of the private key, which must not become known to any other.
In the Diffie–Hellman key exchange scheme, each party generates a public/private key pair and distributes the public key of the pair. After obtaining an authentic (n.b., this is critical) copy of each other's public keys, Alice and Bob can compute a shared secret offline. The shared secret can be used, for instance, as the key for a symmetric cipher which will be, in essentially all cases, much faster.
In this example the message is digitally signed with Alice's private key, but the message itself is not encrypted.
1) Alice signs a message with her private key.
2) Using Alice's public key, Bob can verify that Alice sent the message and that the message has not been modified.

The generation of such key pairs depends on cryptographic algorithms which are based on mathematical problems termed one-way functions.

The Feistel function (F function) of DES

Data Encryption Standard

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Symmetric-key algorithm for the encryption of digital data.

Symmetric-key algorithm for the encryption of digital data.

The Feistel function (F function) of DES
The EFF's US$250,000 DES cracking machine contained 1,856 custom chips and could brute-force a DES key in a matter of days—the photo shows a DES Cracker circuit board fitted with several Deep Crack chips.

Although its short key length of 56 bits makes it too insecure for modern applications, it has been highly influential in the advancement of cryptography.

A sketch of a substitution–permutation network with 3 rounds, encrypting a plaintext block of 16 bits into a ciphertext block of 16 bits. The S-boxes are the Si, the P-boxes are the same P, and the round keys are the Ki.

Block cipher

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A sketch of a substitution–permutation network with 3 rounds, encrypting a plaintext block of 16 bits into a ciphertext block of 16 bits. The S-boxes are the Si, the P-boxes are the same P, and the round keys are the Ki.
Many block ciphers, such as DES and Blowfish utilize structures known as Feistel ciphers
The Lai–Massey scheme. The archetypical cipher utilizing it is IDEA.
Insecure encryption of an image as a result of electronic codebook (ECB) mode encoding.
The development of the boomerang attack enabled differential cryptanalysis techniques to be applied to many ciphers that had previously been deemed secure against differential attacks
One round (two half-rounds) of the RC5 block cipher

In cryptography, a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called blocks.

Edward Larsson's rune cipher resembling that found on the Kensington Runestone. Also includes runically unrelated blackletter writing style and pigpen cipher.

Cipher

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Edward Larsson's rune cipher resembling that found on the Kensington Runestone. Also includes runically unrelated blackletter writing style and pigpen cipher.

In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure.

The Zimmermann Telegram (as it was sent from Washington to Mexico) encrypted as ciphertext.

Ciphertext

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The Zimmermann Telegram (as it was sent from Washington to Mexico) encrypted as ciphertext.
KGB ciphertext found in a hollow nickel in Brooklyn in 1953
The Zimmermann Telegram decrypted into plaintext (and translated into English).
The Shu borough inscription, England

In cryptography, ciphertext or cyphertext is the result of encryption performed on plaintext using an algorithm, called a cipher.

A simple illutration of public-key cryptography, one of the most widely used form of encryption

Encryption

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A simple illutration of public-key cryptography, one of the most widely used form of encryption

In cryptography, encryption is the process of encoding information.

In the Diffie–Hellman key exchange scheme, each party generates a public/private key pair and distributes the public key. After obtaining an authentic copy of each other's public keys, Alice and Bob can compute a shared secret offline. The shared secret can be used, for instance, as the key for a symmetric cipher.

Diffie–Hellman key exchange

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Method of securely exchanging cryptographic keys over a public channel and was one of the first public-key protocols as conceived by Ralph Merkle and named after Whitfield Diffie and Martin Hellman.

Method of securely exchanging cryptographic keys over a public channel and was one of the first public-key protocols as conceived by Ralph Merkle and named after Whitfield Diffie and Martin Hellman.

In the Diffie–Hellman key exchange scheme, each party generates a public/private key pair and distributes the public key. After obtaining an authentic copy of each other's public keys, Alice and Bob can compute a shared secret offline. The shared secret can be used, for instance, as the key for a symmetric cipher.
Illustration of the concept behind Diffie–Hellman key exchange

DH is one of the earliest practical examples of public key exchange implemented within the field of cryptography.

A format of one-time pad used by the U.S. National Security Agency, code named DIANA. The table on the right is an aid for converting between plaintext and ciphertext using the characters at left as the key.

One-time pad

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A format of one-time pad used by the U.S. National Security Agency, code named DIANA. The table on the right is an aid for converting between plaintext and ciphertext using the characters at left as the key.

In cryptography, the one-time pad (OTP) is an encryption technique that cannot be cracked, but requires the use of a single-use pre-shared key that is not smaller than the message being sent.

ROT13 is a Caesar cipher, a type of substitution cipher. In ROT13, the alphabet is rotated 13 steps.

Substitution cipher

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ROT13 is a Caesar cipher, a type of substitution cipher. In ROT13, the alphabet is rotated 13 steps.
An example pigpen message
The forged nomenclator message used in the Babington Plot
A French nomenclator code table
Enigma cipher machine as used by the German military in World War II

In cryptography, a substitution cipher is a method of encrypting in which units of plaintext are replaced with the ciphertext, in a defined manner, with the help of a key; the "units" may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth.