Trouble Verifying the XML Digest

I am currently using Saml2Ruby to integrate with my vendor’s
CA SiteMinder Identity Provider.  After a successful login, I am receiving
a SAML assertion and all of the attributes I need are present.  My problem
is that I cannot generate a matching digest value to verify that the content
has not been tampered with.  It’s my understanding that the digest
should be the assertion => SHA-1 Hashed => Base 64 encoded.  This
currently isn’t matching the digest value in the response from my
vendor.  Can anyone suggest what I may be doing wrong?

 

Thank you,

Mark