[Cryptography] Should the IV of an encryption operation be input to the key derivation function?

[Phillip Hallam-Baker]

Further to my explorations of HKDF (RFC 3394) I am thinking as follows:

Most cryptographic modes use the same key to encrypt a message. CBC, GCM ,
etc all perform operations on the input data, the key is constant.

When using a public key for exchange, we choose a session key which is
random every time. This each message is guaranteed to be encrypted under a
different key.

If I use KDF with a fixed salt (the norm for most protocols) I get
inter-protocol separation but not separation per message. The IV provides
some protection but I am still handing the attacker a possible advantage.

So what if I was to use the IV of the encrypted data as a part of the salt
in the Key derivation function? Is this a good idea or a bad one?
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