1""" 2PostScript Type 1 fonts make use of two types of encryption: charstring 3encryption and ``eexec`` encryption. Charstring encryption is used for 4the charstrings themselves, while ``eexec`` is used to encrypt larger 5sections of the font program, such as the ``Private`` and ``CharStrings`` 6dictionaries. Despite the different names, the algorithm is the same, 7although ``eexec`` encryption uses a fixed initial key R=55665. 8 9The algorithm uses cipher feedback, meaning that the ciphertext is used 10to modify the key. Because of this, the routines in this module return 11the new key at the end of the operation. 12 13""" 14 15from fontTools.misc.textTools import bytechr, bytesjoin, byteord 16 17 18def _decryptChar(cipher, R): 19 cipher = byteord(cipher) 20 plain = ( (cipher ^ (R>>8)) ) & 0xFF 21 R = ( (cipher + R) * 52845 + 22719 ) & 0xFFFF 22 return bytechr(plain), R 23 24def _encryptChar(plain, R): 25 plain = byteord(plain) 26 cipher = ( (plain ^ (R>>8)) ) & 0xFF 27 R = ( (cipher + R) * 52845 + 22719 ) & 0xFFFF 28 return bytechr(cipher), R 29 30 31def decrypt(cipherstring, R): 32 r""" 33 Decrypts a string using the Type 1 encryption algorithm. 34 35 Args: 36 cipherstring: String of ciphertext. 37 R: Initial key. 38 39 Returns: 40 decryptedStr: Plaintext string. 41 R: Output key for subsequent decryptions. 42 43 Examples:: 44 45 >>> testStr = b"\0\0asdadads asds\265" 46 >>> decryptedStr, R = decrypt(testStr, 12321) 47 >>> decryptedStr == b'0d\nh\x15\xe8\xc4\xb2\x15\x1d\x108\x1a<6\xa1' 48 True 49 >>> R == 36142 50 True 51 """ 52 plainList = [] 53 for cipher in cipherstring: 54 plain, R = _decryptChar(cipher, R) 55 plainList.append(plain) 56 plainstring = bytesjoin(plainList) 57 return plainstring, int(R) 58 59def encrypt(plainstring, R): 60 r""" 61 Encrypts a string using the Type 1 encryption algorithm. 62 63 Note that the algorithm as described in the Type 1 specification requires the 64 plaintext to be prefixed with a number of random bytes. (For ``eexec`` the 65 number of random bytes is set to 4.) This routine does *not* add the random 66 prefix to its input. 67 68 Args: 69 plainstring: String of plaintext. 70 R: Initial key. 71 72 Returns: 73 cipherstring: Ciphertext string. 74 R: Output key for subsequent encryptions. 75 76 Examples:: 77 78 >>> testStr = b"\0\0asdadads asds\265" 79 >>> decryptedStr, R = decrypt(testStr, 12321) 80 >>> decryptedStr == b'0d\nh\x15\xe8\xc4\xb2\x15\x1d\x108\x1a<6\xa1' 81 True 82 >>> R == 36142 83 True 84 85 >>> testStr = b'0d\nh\x15\xe8\xc4\xb2\x15\x1d\x108\x1a<6\xa1' 86 >>> encryptedStr, R = encrypt(testStr, 12321) 87 >>> encryptedStr == b"\0\0asdadads asds\265" 88 True 89 >>> R == 36142 90 True 91 """ 92 cipherList = [] 93 for plain in plainstring: 94 cipher, R = _encryptChar(plain, R) 95 cipherList.append(cipher) 96 cipherstring = bytesjoin(cipherList) 97 return cipherstring, int(R) 98 99 100def hexString(s): 101 import binascii 102 return binascii.hexlify(s) 103 104def deHexString(h): 105 import binascii 106 h = bytesjoin(h.split()) 107 return binascii.unhexlify(h) 108 109 110if __name__ == "__main__": 111 import sys 112 import doctest 113 sys.exit(doctest.testmod().failed) 114