OpenSSL::PKCS5.pbkdf2_hmac has been renamed to OpenSSL::KDF.pbkdf2_hmac. This method is provided for backwards compatibility.
# File openssl/lib/openssl/pkcs5.rb, line 13
def pbkdf2_hmac(pass, salt, iter, keylen, digest)
OpenSSL::KDF.pbkdf2_hmac(pass, salt: salt, iterations: iter,
length: keylen, hash: digest)
end