[strongSwan] Strongswan AUTH payload signature hash algorithm for certificate based authentication

[Kalyani Garigipati (kagarigi)]

Hi,

I am trying to bring up ikev2 sa between strongswan and cisco router.
The authentication method used is certificates and prf algorithm is SHA256.


·         I wanted to know what is the hash algorithm that is used while generating the signature in AUTH payload for strongswan.
Is it SHA1 or SHA256 ?


·         I observed that if I generate the signature in AUTH payload using SHA256, it fails the signature validation
If I generate the signature in authentication payload using SHA1 , it passes the signature validation.

RFC quotes below in page 94 of 5996

RSA Digital Signature                  1
      Computed as specified in Section 2.15<https://tools.ietf.org/html/rfc5996#section-2.15> using an RSA private key
      with RSASSA-PKCS1-v1_5 signature scheme specified in [PKCS1<https://tools.ietf.org/html/rfc5996#ref-PKCS1>]
      (implementers should note that IKEv1 used a different method for
      RSA signatures).  To promote interoperability, implementations
      that support this type SHOULD support signatures that use SHA-1
      as the hash function and SHOULD use SHA-1 as the default hash
      function when generating signatures


Regards,
kalyani


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