Electronic Code Book

Electronic Code Book (ECB) is a mode of operation for a block cipher, with the characteristic that each possible block of plaintext has a defined corresponding ciphertext value and vice versa. In other words, the same plaintext value will always result in the same ciphertext value. Electronic Code Book is used when a volume of plaintext is separated into several blocks of data, each of which is then encrypted independently of other blocks. In fact, Electronic Code Book has the ability to support a separate encryption key for each block type.

However, Electronic Code Book is not a good system to use with small block sizes (for example, smaller than 40 bits) and identical encryption modes. This is because some words and phrases may be reused often enough so that the same repetitive part-blocks of ciphertext can emerge, laying the groundwork for a codebook attack where the plaintext patterns are fairly obvious. However, security may be improved if random pad bits are added to each block. On the other hand, 64-bit or larger blocks should contain enough unique characteristics (entropy) to make a codebook attack unlikely to succeed.

In terms of error correction, any bit errors in a ciphertext block affect decryption of that block only. Chaining dependency is not an issue in that reordering of the ciphertext blocks will only reorder the corresponding plaintext blocks, but not affect decryption.

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More resources from around the web: - SearchSecurity.com includes a number of selected links to cryptography papers and tutorials. - RSA Security provides a Frequently Asked Questions section about cryptography and security.

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