Signature Algorithms

The TLSv1.2 protocol made the signature algorithm and the hash algorithm that are used for digital signatures an independent attribute. Previously the negotiated cipher suite determined these algorithms. System SSL has the infrastructure to support multiple signature algorithms.

The ordered list of allowed signature/hash algorithm pairs serves two purposes in TLSv1.2 and has no meaning for prior protocols:
Certificate Selection

The ordered signature algorithm list is sent to the peer when System SSL requests a certificate during the handshake. The peer uses the received list to guide the certificate selection process. The peer should select a certificate that conforms to the list however that is not true for all implementations and configurations. System SSL treats a received certificate with an undesired signature algorithm as a session error unless optional client authentication is configured.

When System SSL receives a certificate request and is unable to select a conforming certificate, it sends an available nonconforming RSA certificate. The peer determines whether this certificate results in a session error. Refer to Multiple Certificate Selection for more details on the System SSL certificate selection logic.

Message Signature
The list of algorithm pairs restricts which signature and hash algorithms can be used for handshake message digital signatures. A TLSv1.2 handshake message signature can be different from the signature of the certificate that is used for the session. For instance, the handshake message can be protected by SHA512 even though an MD5 certificate is selected for the session.
System SSL has the infrastructure to support the following signature algorithms:
  • ECDSA_SHA512
  • ECDSA_SHA384
  • ECDSA_SHA256
  • ECDSA_SHA224
  • ECDSA_SHA1
  • RSA_SHA512
  • RSA_SHA384
  • RSA_SHA256
  • RSA_SHA224
  • RSA_SHA1
  • RSA_MD5

Shipped SSL Supported Signature Algorithms

System SSL is shipped with the following list of supported signature algorithms:
  • ECDSA_SHA512
  • ECDSA_SHA384
  • ECDSA_SHA256
  • ECDSA_SHA224
  • ECDSA_SHA1
  • RSA_SHA512
  • RSA_SHA384
  • RSA_SHA256
  • RSA_SHA224
  • RSA_SHA1
  • RSA_MD5

Shipped SSL Default Signature Algorithms

The following displays the order of the shipped default signature algorithm list:
  • ECDSA_SHA512
  • ECDSA_SHA384
  • ECDSA_SHA256
  • ECDSA_SHA224
  • ECDSA_SHA1
  • RSA_SHA512
  • RSA_SHA384
  • RSA_SHA256
  • RSA_SHA224
  • RSA_SHA1
  • RSA_MD5
The shipped default signature algorithm list can be changed by using System Service Tools (SST) Advanced Analysis Command SSLCONFIG.