Electronic Code Book

Tags

cryptography

A mode of use for block-ciphers which [see page 7, maps] each input block with the same value to the same output-block using a codebook key.

This approach is useful because any error in a block affects [see page 38, only] the decryption of that block.

When one of the transmitted bits in a block has an error (0 read as 1 or vice-versa) that blocks decryption may fail but the rest of the sequence can still be [see page 35, decrypted] accurately without issue.

Note: The key for an ECB is a codebook, and in many situations we may just [see page 4, list] the permutation of possible inputs and the desired output. In [see page 5, practice] we rarely do this, preferring to use a binary-key and a functional algorithm to express the relation between the input and output blocks.

This approach is generally discouraged because it suffers from the same issues as a character-by-character substitution cipher. Structure in the plaintext can be found in the ciphertext. Especially when entropy is very-low because the encrypted result could still be very easily discernible (eg. [see page 9, tux], here we use the alpha-channel in an image to encode certain data. The image is not encrypted (you can easily make it out) even though the pixel/bit-stream is essentially encrypted).