On Jan 31, 2005, at 10:38 PM, Steven M. Bellovin wrote:
When using CBC mode, one should not encrypt more than 2^32 64-bit blocks under a given key. That comes to ~275G bits, which means that on a GigE link running flat out you need to rekey at least every 5 minutes, which is often impractical. Since I've seen Gigabit Ethernet cards for <US$25, this bears thinking about -- and while 10GigE is still too expensive for most people, its prices are dropping rapidly. With 10GigE, you'd have to rekey every 27.5 seconds...
For reference purposes, with AES you'd be safe for 2^64*128 bits. That's a Big Number of seconds.
--Prof. Steven M. Bellovin, http://www.cs.columbia.edu/~smb
I would also like to reinforce Prof. Bellovin's comment that the 3DES block size is too small.
In bulk storage system encryption, 3DES will require rekey every ~~65GBytes. Most PC's have more than this.
With AES the number is ~250 Exabytes (which is 250 billion gigabytes).
Thanks!
jim
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