# Source code for fontTools.misc.eexec

    """
    PostScript Type 1 fonts make use of two types of encryption: charstring
    encryption and ``eexec`` encryption. Charstring encryption is used for
    the charstrings themselves, while ``eexec`` is used to encrypt larger
    sections of the font program, such as the ``Private`` and ``CharStrings``
    dictionaries. Despite the different names, the algorithm is the same,
    although ``eexec`` encryption uses a fixed initial key R=55665.

    The algorithm uses cipher feedback, meaning that the ciphertext is used
    to modify the key. Because of this, the routines in this module return
    the new key at the end of the operation.

    """

    from fontTools.misc.textTools import bytechr, bytesjoin, byteord

    def _decryptChar(cipher, R):
        cipher = byteord(cipher)
        plain = ((cipher ^ (R >> 8))) & 0xFF
        R = ((cipher + R) * 52845 + 22719) & 0xFFFF
        return bytechr(plain), R

    def _encryptChar(plain, R):
        plain = byteord(plain)
        cipher = ((plain ^ (R >> 8))) & 0xFF
        R = ((cipher + R) * 52845 + 22719) & 0xFFFF
        return bytechr(cipher), R

    def decrypt(cipherstring, R):
        r"""
        Decrypts a string using the Type 1 encryption algorithm.

        Args:
                cipherstring: String of ciphertext.
                R: Initial key.

        Returns:
                decryptedStr: Plaintext string.
                R: Output key for subsequent decryptions.

        Examples::

                >>> testStr = b"\0\0asdadads asds\265"
                >>> decryptedStr, R = decrypt(testStr, 12321)
                >>> decryptedStr == b'0d\nh\x15\xe8\xc4\xb2\x15\x1d\x108\x1a<6\xa1'
                True
                >>> R == 36142
                True
        """
        plainList = []
        for cipher in cipherstring:
            plain, R = _decryptChar(cipher, R)
            plainList.append(plain)
        plainstring = bytesjoin(plainList)
        return plainstring, int(R)

    def encrypt(plainstring, R):
        r"""
        Encrypts a string using the Type 1 encryption algorithm.

        Note that the algorithm as described in the Type 1 specification requires the
        plaintext to be prefixed with a number of random bytes. (For ``eexec`` the
        number of random bytes is set to 4.) This routine does *not* add the random
        prefix to its input.

        Args:
                plainstring: String of plaintext.
                R: Initial key.

        Returns:
                cipherstring: Ciphertext string.
                R: Output key for subsequent encryptions.

        Examples::

                >>> testStr = b"\0\0asdadads asds\265"
                >>> decryptedStr, R = decrypt(testStr, 12321)
                >>> decryptedStr == b'0d\nh\x15\xe8\xc4\xb2\x15\x1d\x108\x1a<6\xa1'
                True
                >>> R == 36142
                True

        >>> testStr = b'0d\nh\x15\xe8\xc4\xb2\x15\x1d\x108\x1a<6\xa1'
        >>> encryptedStr, R = encrypt(testStr, 12321)
        >>> encryptedStr == b"\0\0asdadads asds\265"
        True
        >>> R == 36142
        True
        """
        cipherList = []
        for plain in plainstring:
            cipher, R = _encryptChar(plain, R)
            cipherList.append(cipher)
        cipherstring = bytesjoin(cipherList)
        return cipherstring, int(R)

    def hexString(s):
        import binascii

        return binascii.hexlify(s)

    def deHexString(h):
        import binascii

        h = bytesjoin(h.split())
        return binascii.unhexlify(h)

    if __name__ == "__main__":
        import sys
        import doctest

        sys.exit(doctest.testmod().failed)