Extract and verify SSL signature form x509 certificate.

I've a x509 certificate from my CA self-signed: $res_ca_cert=openssl_csr_sign($res_ca_csr,NULL,$res_ca_key,365); Then, I've an user certificate signed by the CA: $res_usr_cert=openssl_csr_sign($txt_usr_csr,$txt_ca_cert,$res_ca_key,1); Exists in the PHP API any function to check if the user certificate is really signed by the CA ? Like this operation : $res_ca_public = openssl_get_publickey($txt_ca_cert); $txt_usr_sign = fakessl_x509_getsignature($txt_usr_cert); openssl_public_decrypt($txt_usr_sign,$txt_usr_public,$res_ca_public); Check that $txt_usr_public == fakessl_gettxt_publickey($txt_usr_cert) I've found openssl_pkcs7_verify, but this doesn't work for me because I can access to the file system. Another solutions is to parse the human-readable x509 certificates in order to get the public keys and certificates and verify it by hand. Any idea ? Thanks for all !