KDF(key_str, salt [, {info | iterations} [, kdf_name [, width ]]])

kdf_name is "hkdf" or "pbkdf2_hmac" (default).

width (in bits) can be any number divisible by 8,
by default it's taken from @@block_encryption_mode

iterations must be positive, and is 1000 by default

OpenSSL 1.0 doesn't support HKDF, so it'll return NULL.
This OpenSSL version is still used in SLES 12 and CentOS 7