After extensive research, the closest thing we have to that is in Net::SSLeay, which has bindings to a ton of low-level openssl functions. In v1.83 2018-01-06 they added these: 
    X509_STORE_CTX_new and X509_verify_cert

[download]
but I couldn't get past related segfaults and there's not much documentation on there. So I ended up doing:
  1. use Convert::ASN1 to re-encode the tbsCertificate data I had decoded in my PKCS#7 file ("tbs" it turns out is "to-be-signed")
  2. get the signature from the PCKS#7 file
  3. get the subjectPublicKeyInfo.subjectPublic Key from the cert that signed this cert
  4. feed that to $signer_key = Crypt::OpenSSL::RSA->new_public_key($signer_key_pem);
  5. and then do $signer_key->verify($cert_as_signed, $signature)
and wash, rinse, repeat for each of the certs in the chain.

In reply to Re: How to validate signature of a RSA/x509 cert in Perl by kgoess
in thread How to validate signature of a RSA/x509 cert in Perl by kgoess

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