48 bits => 32 bits(8*6 => 8*4)
2 bits used to select amongst 4 substitutions for the rest of the 4-bit quantity
Security of DES
– key space is too small(2^56 keys)
Exhaustive key search relative easy with today’s computer
– S-box design criteria have been kept secret
– Highly resistant to cryptanalysis techniques published years after DES
Triple DES
(a)Encryption p -> E -> D -> E -> C
(b)Decryption: C -> D -> E -> D -> P
K1=K3 result in an equivalant 112-bit DES which provides a sufficient key space
Distinct K1, K2, K3 results in an even stronger 168-bit DES
Can run as a single DES with K1 = K2
Advanced Encryption Standard
In 1997, the U.S. National Institute for Standards and Technology(NIST) put out a public call for a replacement to DES
It narrowed down the list of submissions o five finalists, and ultimately chose an algorithm(Rijndael) that is now known as the Advanced Encryption Standard
New (Nov. 2001) symmetric-key NIST standard, replacing DES
Processes data in 128 bit blocks
Key length can be 128, 192, or 256 bit
