These functions load the certificates and private keys into the SSL_CTX or SSL object, respectively.
The SSL_CTX_* class of functions loads the certificates and keys into the SSL_CTX object ctx. The information is passed to SSL objects ssl created from ctx with SSL_new(3) by copying, so that changes applied to ctx do not propagate to already existing SSL objects.
The SSL_* class of functions only loads certificates and keys into a specific SSL object. The specific information is kept, when SSL_clear(3) is called for this SSL object.
SSL_CTX_use_certificate() loads the certificate x into ctx, SSL_use_certificate() loads x into ssl. The rest of the certificates needed to form the complete certificate chain can be specified using the SSL_CTX_add_extra_chain_cert(3) function.
SSL_CTX_use_certificate_ASN1() loads the ASN1 encoded certificate from the memory location d (with length len) into ctx, SSL_use_certificate_ASN1() loads the ASN1 encoded certificate into ssl.
SSL_CTX_use_certificate_file() loads the first certificate stored in file into ctx. The formatting type of the certificate must be specified from the known types SSL_FILETYPE_PEM, SSL_FILETYPE_ASN1. SSL_use_certificate_file() loads the certificate from file into ssl. See the NOTES section on why SSL_CTX_use_certificate_chain_file() should be preferred.
SSL_CTX_use_certificate_chain_file() loads a certificate chain from file into ctx. The certificates must be in PEM format and must be sorted starting with the subject's certificate (actual client or server certificate), followed by intermediate CA certificates if applicable, and ending at the highest level (root) CA. There is no corresponding function working on a single SSL object.
SSL_CTX_use_PrivateKey() adds pkey as private key to ctx. SSL_CTX_use_RSAPrivateKey() adds the private key rsa of type RSA to ctx. SSL_use_PrivateKey() adds pkey as private key to ssl; SSL_use_RSAPrivateKey() adds rsa as private key of type RSA to ssl. If a certificate has already been set and the private does not belong to the certificate an error is returned. To change a certificate, private key pair the new certificate needs to be set with SSL_use_certificate() or SSL_CTX_use_certificate() before setting the private key with SSL_CTX_use_PrivateKey() or SSL_use_PrivateKey().
SSL_CTX_use_PrivateKey_ASN1() adds the private key of type pk stored at memory location d (length len) to ctx. SSL_CTX_use_RSAPrivateKey_ASN1() adds the private key of type RSA stored at memory location d (length len) to ctx. SSL_use_PrivateKey_ASN1() and SSL_use_RSAPrivateKey_ASN1() add the private key to ssl.
SSL_CTX_use_PrivateKey_file() adds the first private key found in file to ctx. The formatting type of the certificate must be specified from the known types SSL_FILETYPE_PEM, SSL_FILETYPE_ASN1. SSL_CTX_use_RSAPrivateKey_file() adds the first private RSA key found in file to ctx. SSL_use_PrivateKey_file() adds the first private key found in file to ssl; SSL_use_RSAPrivateKey_file() adds the first private RSA key found to ssl.
SSL_CTX_check_private_key() checks the consistency of a private key with the corresponding certificate loaded into ctx. If more than one key/certificate pair (RSA/DSA) is installed, the last item installed will be checked. If e.g. the last item was a RSA certificate or key, the RSA key/certificate pair will be checked. SSL_check_private_key() performs the same check for ssl. If no key/certificate was explicitly added for this ssl, the last item added into ctx will be checked.