I have wrapper functions for a good deal of the OpenSSL pki code right now.

   cert=EzCrypto::Verifier.from_file "testsigner.cert"
    assert_equal cert.email,"pelleb@gmail.com"
    assert_equal cert.country,"DK"
    assert_equal cert.state,"Denmark"
    assert_equal cert.locality,"Copenhagen"
    assert_equal cert.organisational_unit,"testing"
    assert_equal cert.organisation,"EzCrypto Test Certificate"
    assert_equal cert.organizational_unit,"testing"
    assert_equal cert.organization,"EzCrypto Test Certificate"
    assert_equal cert.name,"EzCrypto Testing"
    assert_equal cert.common_name,"EzCrypto Testing"

Trust stores are supported:

    trust=EzCrypto::TrustStore.new
    valicert=EzCrypto::Verifier.from_file "valicert_class2_root.crt"
    starfield=EzCrypto::Verifier.from_file "sf_issuing.crt"
    wideword=EzCrypto::Verifier.from_file "wideword.net.cert"
    trust.add valicert    
    trust.add starfield
    assert trust.verify(wideword)

Still missing are CRLs and OCSP.

If you want to play with it before release get it from:

svn://rubyforge.org//var/svn/ezcrypto/trunk/ezcrypto