The instance method OpenSSL::PKCS7::SignerInfo.name does not return the signing certificate name but the X509 name of the signer's issuer. This is because SignerInfo.name is actually an alias of SignerInfo.issuer. This appears to be a mistake particularly because OpenSSL::PKCS7::RecepientInfo doesn't have a corresponding name method.
Perhaps OpenSSL::PKCS7::SignerInfo.name should be considered for removal since the method name is misleading.
Updated by Jacob640 (Joseph Coyle) about 6 years ago
Because of this bug I have been looking at why it is so difficult to get useful identifying info for pkcs7 signers. I see that OpenSSL provides a utility function to extract a certificate from a pkcs7 message corresponding to a supplied signer info struct called PKCS7_cert_from_signer_info.
Unfortunately due to OpenSSL closely following the pkcs7 data structures SignerInfo structs do not appear to contain the certificate or name of the signing certificate. Because of this PKCS7_cert_from_signer_info requires both a pkcs7 message and a signerInfo struct to provide the signer certificates.
However if we wish to follow the design decisions of OpenSSL it is fairly easy to construct a utility method for OpenSSL::PKCS7 that takes a SignerInfo object and outputs the corresponding certificate. I have written a basic demonstration in this commit: https://github.com/Jacob640/ruby/commit/10e5f0b74cd08ee23f2b6643a7f86a6dbec857c1