At 10:24 PM 10/5/95 -0400, Adam Shostack <adam@homeport.org> wrote:
The key does indeed have a high likelihood of being unique, but dealing with 1024 bit identifiers could strain database systems, especially when 100 well chosen bits would be than enough.
If everybody in the world has a 1024-bit key, that's 750 GB; that's not bad at all by the time everybody in the world would have one, and you could do MD5s in about 100 GB, which is a little more convenient. Today, for 750 GB, you'd probably have tape in your system, or optical jukebox. But not everybody has one; on the other hand, I suppose individuals in well-heeled countries might end up with dozens of their own. On the other hand, the number of 1024-bit primes is something like 2^1023/log(2^1024) (if I remember right), or roughly 2^1013. The probability of two independent uniformly distributed primes matching is about 2^1023/2^32, which is still an astoundingly mindbogglingly LARGE number. If you've got 1024 bits of entropy in your input process, there will not _be_ any matches. (If people insist on using sources of randomness like clocks or user names, the chances are a lot higher....) Now, for 128-bit hashes, whether it's MD5 or just the near-bottom 128 key bits, by the time you get 2^64 of them together, you've got a 50% chance of a match. Not a problem, since you'll not likely need that many, even for the 2^33 people in the world. Still not a problem. #--- # Thanks; Bill # Bill Stewart, Freelance Information Architect, stewarts@ix.netcom.com # Phone +1-510-247-0664 Pager/Voicemail 1-408-787-1281 #---