def METHOD_NAME(data, marker, passphrase=None, randfunc=None):
    """Encode a piece of binary data into PEM format.
    Args:
      data (byte string):
        The piece of binary data to encode.
      marker (string):
        The marker for the PEM block (e.g. "PUBLIC KEY").
        Note that there is no official master list for all allowed markers.
        Still, you can refer to the OpenSSL_ source code.
      passphrase (byte string):
        If given, the PEM block will be encrypted. The key is derived from
        the passphrase.
      randfunc (callable):
        Random number generation function; it accepts an integer N and returns
        a byte string of random data, N bytes long. If not given, a new one is
        instantiated.
    Returns:
      The PEM block, as a string.
    .. _OpenSSL: https://github.com/openssl/openssl/blob/master/include/openssl/pem.h
    """
    if randfunc is None:
        randfunc = get_random_bytes
    out = "-----BEGIN %s-----\n" % marker
    if passphrase:
        # We only support 3DES for encryption
        salt = randfunc(8)
        key = PBKDF1(passphrase, salt, 16, 1, MD5)
        key += PBKDF1(key + passphrase, salt, 8, 1, MD5)
        objenc = DES3.new(key, DES3.MODE_CBC, salt)
        out += "Proc-Type: 4,ENCRYPTED\nDEK-Info: DES-EDE3-CBC,%s\n\n" %\
            tostr(hexlify(salt).upper())
        # Encrypt with PKCS#7 padding
        data = objenc.encrypt(pad(data, objenc.block_size))
    elif passphrase is not None:
        raise ValueError("Empty password")
    # Each BASE64 line can take up to 64 characters (=48 bytes of data)
    # b2a_base64 adds a new line character!
    chunks = [tostr(b2a_base64(data[i:i + 48]))
              for i in range(0, len(data), 48)]
    out += "".join(chunks)
    out += "-----END %s-----" % marker
    return out