def crypto_pwhash_scryptsalsa208sha256_ll(passwd, salt, n, r, p, dklen=64,
                                          maxmem=SCRYPT_MAX_MEM):
    """
    Derive a cryptographic key using the ``passwd`` and ``salt``
    given as input.

    The work factor can be tuned by by picking different
    values for the parameters

    :param bytes passwd:
    :param bytes salt:
    :param bytes salt: *must* be *exactly* :py:const:`.SALTBYTES` long
    :param int dklen:
    :param int opslimit:
    :param int n:
    :param int r: block size,
    :param int p: the parallelism factor
    :param int maxmem: the maximum available memory available for scrypt's
                       operations
    :rtype: bytes
    """
    ensure(isinstance(n, integer_types),
           raising=TypeError)
    ensure(isinstance(r, integer_types),
           raising=TypeError)
    ensure(isinstance(p, integer_types),
           raising=TypeError)

    ensure(isinstance(passwd, bytes),
           raising=TypeError)
    ensure(isinstance(salt, bytes),
           raising=TypeError)

    _check_memory_occupation(n, r, p, maxmem)

    buf = ffi.new("uint8_t[]", dklen)

    ret = lib.crypto_pwhash_scryptsalsa208sha256_ll(passwd, len(passwd),
                                                    salt, len(salt),
                                                    n, r, p,
                                                    buf, dklen)

    ensure(ret == 0, 'Unexpected failure in key derivation',
           raising=exc.RuntimeError)

    return ffi.buffer(ffi.cast("char *", buf), dklen)[:]
Derive a cryptographic key using the ``passwd`` and ``salt``
    given as input.

    The work factor can be tuned by by picking different
    values for the parameters

    :param bytes passwd:
    :param bytes salt:
    :param bytes salt: *must* be *exactly* :py:const:`.SALTBYTES` long
    :param int dklen:
    :param int opslimit:
    :param int n:
    :param int r: block size,
    :param int p: the parallelism factor
    :param int maxmem: the maximum available memory available for scrypt's
                       operations
    :rtype: bytes