What is the hash of this cipher: TLS_RSA_WITH_AES_128_CCM In TLS 1.3 supported ciphersuite,  I find the following ciphersuite:


  TLS_RSA_WITH_AES_128_CCM


Can any one tell me what is the hash function used in this ciphersuite? how could you know that (reference please).
In draft 14, which is not the latest draft at the time of writing there are two places where a hash is used: the one for signature generation / verification using the private key / public key pair of the leaf certificate and the one used as configuration parameter for HKDF (session key derivation) 

For signature generation / verification

TLS_RSA_WITH_AES_128_CCM doesn't exist, only  TLS_DHE_RSA_WITH_AES_128_CCM exists which is similar but uses a different key agreement protocol. RSA for key agreement was explicitly deprecated for TLS 1.3. In the RFC the ciphersuite can be represented by TLS_AES_128_CCM_SHA256; beware that the DH key agreement scheme - if that is used instead of ECDH - differs ever so slightly though (disclosure: sorry, I did that).       

RSA uses the supported_signature_algorithms extension to select the hash configuration parameter within the signature generation function. This is specified clearly in section 4.2.2.  Signature Algorithms.

For key derivation

The hash is after the (EC)DHE key agreement operation to derive the session keys. This will always use HKDF, as specified in appendix A.4:


  Cipher suite names that lack a "HASH" value that are defined for use
  with TLS 1.2 or later use the SHA-256 hash algorithm by default.