How long will that crypto key be useful?

One of the crypto guys here pointed this out to me last night, it's kinda cool. A small web-app to determine how long a key should be to provide adequate protection up to a specified year. There are a few other options in there too...

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  1. Interesting site. One thing that a lot of newbie cryptographers miss is the difference between key length and key entropy. For example, you need thousands of bits of keying material from a Diffe-Hellman exchange in order to produce hundreds of bits of keying material suitable for a symmetric algorithm like AES.

    Google Claude Shannon and entropy for some interesting reading. There’s also a good introductory discussion in Schneier’s Applied Cryptography.

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