To know why you require N number of plaintexts attacks, you would need to know how DES works. (Based on XOR's and the Feistel Cipher) If you would like to know, The DES algorithm is public record. You can go to the below link to read about the algorithm. DES actually has 4 operating modes. You can read about them online as well. (This publication has block diagrams and all.) http://www.csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf DES is actually a 64 bit block cipher.(Technically but a little shake and bake here and there) DES uses 8 bits for error checking (Odd parity on each byte) which is why people call it a 56 bit cipher. People are using Triple Data Encryptions Algorithm (TDEA) or Triple DES (3DES) because DES was broken using a brute force attack in 56 hours using recycled PC boards. (July 15, 1998) The immediate fix was to go to TDEA. Like Jeremy stated, 3DES is relatively computationally secure. (Computationally secure means that if the best algorithm for breaking a crypto system takes at least N operations where N is some specified, very large number. Essentially too large to exhaustively search) If your interested in this field of study Worcester Polytechnic Institute has an Excellent graduate program in Cryptography and Info Security. Chris -------------------------------------------------------- Christopher DeMello Component Engineering General Dynamics C4 Systems Taunton: 508.880.4468 (Th, F) Needham: 781.455.5724 (M, T, W) Christopher.DeMelloat_private -----Original Message----- From: Jeremy Epstein [mailto:jeremy.epsteinat_private] Sent: Monday, March 10, 2003 12:25 PM To: Kryptik Logik; secprogat_private Subject: RE: Some questions on DES Encryption... Depends on why you're asking. If you're researching crypto, sci.crypt.research is probably a better place to ask. If you're worried about someone attacking our crypto, you're worried about the wrong thing. Even 56 bit DES is strong enough that an attacker will almost always attack something else before they attack the crypto. > -----Original Message----- > From: Kryptik Logik [mailto:kryptiklogikat_private] > Sent: Saturday, March 08, 2003 3:57 PM > To: secprogat_private > Subject: Some questions on DES Encryption... > > > > > I'm not too sure whether this is the right forum to ask this but I > > couldn't find a Crypto mailing list so here goes: > > > > I have a few questions on the DES Encryption algorithm: > > > > 1. In DES algorithm, given an encrypted text and the > corresponding plain > > text for that is it possible to retrieve the key. > Essentially, how secure > > is DES to known-plain text attack. I read some where that it is quite > > resistant requiring 2^55 plain texts to get the key but why > is this so? > > What particular feature of the algorithm makes it this way? > > > > # klogik >
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