According to RFC5246 A.5 there are cipher suites TLS_DH_RSA_* and TLS_DH_DSS_*.
How / where does the signature algorithm RSA resp. DSA from the cipher suite come into play when using (non-ephermal) Diffie-Hellman key exchange ?
To my understanding, when using (non-ephermal) DH, key exchange between client and server during the TLS handshake works as follows (suppose there is no client certificate):
- Server sends its certificate in ServerCertificate message to the client. The certificate includes DH-parameters p, g and the server's public key constituent g^x mod p (RFC3279, 2.3.3, RFC 5246, 8.1.2).
- After verifying the certificate, the client chooses private y, computes g^y mod p and sends public key constituent g^y mod p in the ClientKeyExchange message to the server.
- The common private key g^(xy) mod p is known to client and server.
As far as I can see, there is no need for a signature here (up to the certificate's own signature, of course), since public visible g^y mod p is of no help for an attacker due to hardness of computing a discrete logarithm.
Added: No duplicate because the linked question in the comments asks for forward security while this question asks about the notation of the cipher suite.