Acrónimos: CTR
Ver:
·
[NIST-SP800-38A:2001]
·
[FIPS-81:1980]
·
Criptografía
de clave secreta
·
http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation
Al igual que el modo OFB, el modo CTR transforma un
algoritmo de cifrado por bloques en un algoritmo de cifrado de flujo. La
máscara de cifrado se genera cifrando un contador. Además de las ventajas del
modo OFB, permite un acceso aleatorio a la información.
(N) A block cipher mode that
enhances ECB mode by ensuring that each encrypted block is different from every
other block encrypted under the same key. [SP38A] (See:
block cipher.) [RFC4949:2007]
Like OFB, counter mode turns
a block cipher into a stream cipher. It generates the next keystream block by
encrypting successive values of a "counter". The counter can be any
simple function which produces a sequence which is guaranteed not to repeat for
a long time, although an actual counter is the simplest and most popular. CTR
mode has similar characteristics to OFB, but also allows a random access
property during decryption, and is believed to be as secure as the block cipher
being used. Note that the nonce in this graph is the same thing as the
initialization vector (IV) in the other graphs. The IV/nonce and the counter
can be concatenated, added, or XORed together to produce the actual unique
counter block for encryption.
http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation