Maybe you misunderstood. When using CBC mode of operation (the most common one) you have to periodically change the encryption key to protect your data. If an attacker finds two ciphertexts with the same value, then they can starting getting information about the plaintext. Statistically this is has a 50-50 chance of happening after B64 = 2^(n/2) ciphertexts. if n == 64 (like DES) this will be (2^32 * 64bit = 32GByte). For 128bit block ciphers B128 = 2^64 * 128 = 2^32 * 2 * B64. So don't worry about changing VPN session keys in your lifetime. JLC On Sat, Jun 08, 2002 at 04:46:38PM +0100, Newsmail wrote: > as I remember I was told that blowfish has a 32gig limitation before it > begins to generate equal ciphertexts. actually I dont know from which > caracteristique of blowfish this comes from, could somebody clear my mind? > and maybe could somebody tell me how to calculate this limitation for other > 128bit ciphers like AES for exemple? or just tell me what is AES-s limit > actually :> > thx > greg > > > - > Linux-crypto: cryptography in and on the Linux system > Archive: http://mail.nl.linux.org/linux-crypto/ -- http://www.certainkey.com Suite 4560 CTTC 1125 Colonel By Dr. Ottawa ON, K1S 5B6 C: 613.263.2983 - Linux-crypto: cryptography in and on the Linux system Archive: http://mail.nl.linux.org/linux-crypto/
