What is MD5?
MD5 is what takes your passphrase and scrambles it into an IDEA key. In theory, MD5 should generate a different output for every possible bit combination as long as your key space is equal to or larger than 2^128. Proving that MD5 will generate all 2^128 outputs from a given key space equal to 2^128 is practically impossible. This would be about the same as a brute force search on the IDEA key. An interesting problem is that theoretically you can produce an equivalent passphrase by searching any given key space that is 2^128 or larger. In light of the attack on MD5, wait and watch. While a weakness has been found, the jury is still out on using unmodified MD5. A move to SHA or other hash function may be in the future for PGP.
