I propose this option not because its the best but because its what the
two versions I've tested use: viz Netscape Messenger and Microsoft
If you permit a larger key length then it may break an existing
implementation that assumes that the the keylength is X/8. It would
break mine for example but I can fix that.
I can't comment on whether the above implementations assume X/8, can
anyone else? If no one knows then I can do some tests and post the
results back here.
As for this being more complicated to code and test I'd say that depends
on the implementation. Currently, for example, SSLeay would need some
modification to support option 2 with its envelope routines whereas
option 1 is already supported.
There is a standard that that sort of defines it. The standard I'm
referring to is PKCS#12 password based encryption. In this case the
keylength is specifically implied by the algorithm as X/8.
Dr Stephen N. Henson. UK based freelance Cryptographic Consultant.
For info see homepage at http://www.drh-consultancy.demon.co.uk/
PGP key: via homepage.