Block cipher

In cryptography, a block cipher is a symmetric key cipher which operates on a groups of bits of fixed length, called blocks, using an exact transformation. During encryption, a block cipher algorithm might take (for example) a 128-bit block of plaintext as input, and output a corresponding 128-bit block of ciphertext. The exact transformation is controlled using a second input — the secret key. Decryption is similar: the decryption algorithm takes, in this example, a 128-bit block of ciphertext together with the secret key, and output the original 128-bit block of plaintext.

One of the early block cipher designs was the Data Encryption Standard (DES), developed at IBM and published as a standard in 1977. A successor to DES, the Advanced Encryption Standard (AES); also using block cipher, was adopted in 2001. RC5 is a simple symmetric-key made by Ronald Rivest in 1994. RC6 is another made from RC5. RC stands for "Rivest Cipher", or alternatively, "Ron's Code".

Block Cipher Media

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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.

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  Many block ciphers, such as DES and Blowfish utilize structures known as Feistel ciphers

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  The Lai–Massey scheme. The archetypical cipher utilizing it is IDEA.

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  Insecure encryption of an image as a result of electronic codebook (ECB) mode encoding

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  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

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  One round (two half-rounds) of the RC5 block cipher