Question

I am using the following to get the PEM certificate for a connected session in openssl C. What I need is to get a base64 encoded certificate.

if(this->ssl) {
  X509 *cert = SSL_get_certificate(this->ssl);
  EVP_PKEY *pubKey = X509_get_pubkey(cert);
  LOG_INFO("Public key is " << BN_bn2hex(pubKey->pkey.rsa->n));
}

Any information on how can I achieve this would be helpful.

Answer 1

You should use i2d_X509 function to get DER encoded certificate.
Then use your favorite base64 encoder and encode it to PEM.
Do not forget to add —–BEGIN CERTIFICATE—– and —–END CERTIFICATE—– if you want it proper way.

Here you may find example on how to encode with OpenSSL itself.
In using OpenSSL you may simplify things by using i2d_X509_bio function to put DER encoded data directly into BIO.