This memo defines a new Session Description Protocol (SDP) attribute for exchanging Diffie-Hellman (DH) public keys. The attribute is an SDP session-level attribute for describing DH keys, and there is a new media-level parameter for describing public keying material for SRTP key generation. The SDP attribute supports the key establishment schemes of NIST Draft Special Publication 800-56, adds domain parameters and supports external authentication of the DH endpoint without a public key infrastructure.