cryptography - Why DES can be used only with 56bit key? And why the plaintext must be 64 bits in length? -


why des can used 56bit key? happens if use longer key? also, why plaintext must 64 bits in length?

us regulations @ time required users of stronger 56-bit keys, submit "key recovery" enable law enforcement back-door access.

thus des, standard, specified @ maximum allowed key length of 56 bits. if used longer key, not compatible other des systems.

see: http://en.wikipedia.org/wiki/56-bit_encryption

if implementing system & have choice of encryption, more modern & stronger ciphers absolutely recommended. current standard aes (advanced encryption system) available, strong , allows key sizes 128 - 256 bits.

for desktop or server applications, aes-256 default choice.

see: http://en.wikipedia.org/wiki/advanced_encryption_standard

when encrypting data, plaintexts must "padded" minimum size. ciphers rely on jumbling , interactions between multiple bits, preserve secrecy of plaintext & avoid potentially revealing key. short plaintext without padding, jumbling , interactions removed factor & mathematical complexity drops vastly.

encrypting single character without padding, example 'y' or 'n' response, example reduce 2^256 keyspace down possibly 2^24. cracked in minutes. enable attacker guess large parts of key, rapidly break it, , (worst of all) -- decrypt other traffic on channel.


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