#if FROMFILE
BIO* bio = BIO_new_file(filename, "rb");
if (bio == null) goto err;
#else
BIO* bio = BIO_new(BIO_s_mem());
BIO_write(bio, data, dataLen);
#endif
X509* x509 = PEM_read_bio_X509(bio, NULL, NULL, NULL);
if (x509 == null) goto err;
#if OPENSSL_11
ASN1_TIME* notBefore = X509_get0_notBefore(x509);
#else
ASN1_TIME* notBefore = x509->validity->notBefore;
#endif
// Choose a time representation and convert the ASN1_TIME to it.
goto cleanup;
err:
// Exercise left to the reader.
cleanup:
// Don't free notBefore, since it was obtained via a get0 or interior pointer.
if (x509) X509_free(x509);
if (bio) BIO_free(bio);
double possible de [Comment déterminer la date d'expiration SSL cert de un certificat encodé PEM?] (https://stackoverflow.com/questions/21297853/how-to-determine-ssl-cert-expiration-date-from-a-pem-encoded-certificate) – beny23