ParagonIE_Sodium_Compat::crypto_kdf_derive_from_key

    public static function crypto_kdf_derive_from_key(
        $subkey_len,
        $subkey_id,
        $context,
        $key
    ) {
        ParagonIE_Sodium_Core_Util::declareScalarType($subkey_len, 'int', 1);
        ParagonIE_Sodium_Core_Util::declareScalarType($subkey_id, 'int', 2);
        ParagonIE_Sodium_Core_Util::declareScalarType($context, 'string', 3);
        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 4);
        $subkey_id = (int) $subkey_id;
        $subkey_len = (int) $subkey_len;
        $context = (string) $context;
        $key = (string) $key;

        if ($subkey_len < self::CRYPTO_KDF_BYTES_MIN) {
            throw new SodiumException('subkey cannot be smaller than SODIUM_CRYPTO_KDF_BYTES_MIN');
        }
        if ($subkey_len > self::CRYPTO_KDF_BYTES_MAX) {
            throw new SodiumException('subkey cannot be larger than SODIUM_CRYPTO_KDF_BYTES_MAX');
        }
        if ($subkey_id < 0) {
            throw new SodiumException('subkey_id cannot be negative');
        }
        if (ParagonIE_Sodium_Core_Util::strlen($context) !== self::CRYPTO_KDF_CONTEXTBYTES) {
            throw new SodiumException('context should be SODIUM_CRYPTO_KDF_CONTEXTBYTES bytes');
        }
        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_KDF_KEYBYTES) {
            throw new SodiumException('key should be SODIUM_CRYPTO_KDF_KEYBYTES bytes');
        }

        $salt = ParagonIE_Sodium_Core_Util::store64_le($subkey_id);
        $state = self::crypto_generichash_init_salt_personal(
            $key,
            $subkey_len,
            $salt,
            $context
        );
        return self::crypto_generichash_final($state, $subkey_len);
    }