dhkam

Overview ¶

dhkam implements the Diffie Hellman Key Agreement Method using the RFC 3526 Group 14 modulus, and uses blinded key generation.

The package supports using the shared key as a static key, and using the shared key to compute a KEK, implementing the system described in RFC 2631.

The shared key may be retrieved using the SharedKey method. A KEK must first be initialised using the InitializeKEK function, which returns a set of KEK paramaters stored in a KEK type. This can be combined with the `CEK` method on private keys to derive an appropriate CEK.

For example, to generate a KEK for use with AES128CBC with an HMAC-SHA256 MAC:

prv, err := dhkam.GenerateKey(rand.Reader)
if err != nil {
	// ...
}

// pub is a *dhkam.PublicKey containing the public key
// of the party for whom we share this KEK.
kek := prv.InitializeKEK(rand.Reader, pub,
	dhkam.KEKAES128CBCHMACSHA256, nil, sha256.New())
if kek == nil {
	// an error occurred while initialising the KEK.
}

We can generate a CEK from this with:

key, err := prv.CEK(kek)
if err != nil {
	// ...
}

aesKey := key[:16]	// 16 bytes is AES-128 key length.
hmacKey := key[16:]	// the rest of the key is the HMAC key.