=over 4
-=item B<EVP_KDF_HKDF_MODE_EXTRACT_AND_EXPAND> "EXTRACT_AND_EXPAND"
+=item "EXTRACT_AND_EXPAND" or B<EVP_KDF_HKDF_MODE_EXTRACT_AND_EXPAND>
This is the default mode. Calling L<EVP_KDF_derive(3)> on an EVP_KDF_CTX set
up for HKDF will perform an extract followed by an expand operation in one go.
In this mode the digest, key, salt and info values must be set before a key is
derived otherwise an error will occur.
-=item B<EVP_KDF_HKDF_MODE_EXTRACT_ONLY> "EXTRACT_ONLY"
+=item "EXTRACT_ONLY" or B<EVP_KDF_HKDF_MODE_EXTRACT_ONLY>
In this mode calling L<EVP_KDF_derive(3)> will just perform the extract
operation. The value returned will be the intermediate fixed-length pseudorandom
The digest, key and salt values must be set before a key is derived otherwise
an error will occur.
-=item B<EVP_KDF_HKDF_MODE_EXPAND_ONLY> "EXPAND_ONLY"
+=item "EXPAND_ONLY" or B<EVP_KDF_HKDF_MODE_EXPAND_ONLY>
In this mode calling L<EVP_KDF_derive(3)> will just perform the expand
operation. The input key should be set to the intermediate fixed-length