Assume that party 1 and party 2 each possess a key used for AES encrypting data. Assume that the key was properly randomly generated and securely passed between them.
Now I need a way for party 1 to tell party 2 which stored key to use. I was thinking of simply creating an SHA1 hash of the key and sending that with the message. My reasoning is that party 2 can easily compare that hash with the hashes of all their stored keys but there is no way for an attacked to recover the key from only it's hash.
My requirements are protection from casual snooping, not protection from people with supercomputers trying to crack this individual message. Ideally I want the only information that party 1 and party 2 share about each other is the value of the secret encryption key.
Is this plan flawed in any way, and if so is there a better way?