X509_find_by_issuer_and_serial
x509 = X509_find_by_issuer_and_serial(cert, ias->issuer, ias->serial);
return(X509_find_by_issuer_and_serial(p7->d.sign->cert,
signer = X509_find_by_issuer_and_serial (certs,
X509_find_by_issuer_and_serial(p7->d.sign->cert,
X509 *X509_find_by_issuer_and_serial(STACK_OF(X509) *sk,X509_NAME *name,