string to be used as secret key

[David Spades]

Hi all,

I'm trying to create a secret key string for my mac. I have 2 questions:
1. will there be a problem if I include chinese, japanese, cyrillic characters in the secret key string?
2. what's the best length for the secret key?

Thanks

[Tim Holloway]

In theory, a key can be any sequence of binary characters, since encryption is usually done using octets. Specific encryption/decryption software may not be as flexible, however. What mechanisms are you planning to use?

[David Spades]

still doing some research, but most likely hmac sha256. also, is it safe to have one secret key per application as opposed to 1 secret key per user? and how often should I change the secret key? or can I use the same secret key forever? thanks