src/third_party/tlslite/tlslite/utils/Python_AES.py

   1 """Pure-Python AES implementation."""
   2
   3 from cryptomath import *
   4
   5 from AES import *
   6 from rijndael import rijndael
   7
   8 def new(key, mode, IV):
   9     return Python_AES(key, mode, IV)
  10
  11 class Python_AES(AES):
  12     def __init__(self, key, mode, IV):
  13         AES.__init__(self, key, mode, IV, "python")
  14         self.rijndael = rijndael(key, 16)
  15         self.IV = IV
  16
  17     def encrypt(self, plaintext):
  18         AES.encrypt(self, plaintext)
  19
  20         plaintextBytes = stringToBytes(plaintext)
  21         chainBytes = stringToBytes(self.IV)
  22
  23         #CBC Mode: For each block...
  24         for x in range(len(plaintextBytes)/16):
  25
  26             #XOR with the chaining block
  27             blockBytes = plaintextBytes[x*16 : (x*16)+16]
  28             for y in range(16):
  29                 blockBytes[y] ^= chainBytes[y]
  30             blockString = bytesToString(blockBytes)
  31
  32             #Encrypt it
  33             encryptedBytes = stringToBytes(self.rijndael.encrypt(blockString))
  34
  35             #Overwrite the input with the output
  36             for y in range(16):
  37                 plaintextBytes[(x*16)+y] = encryptedBytes[y]
  38
  39             #Set the next chaining block
  40             chainBytes = encryptedBytes
  41
  42         self.IV = bytesToString(chainBytes)
  43         return bytesToString(plaintextBytes)
  44
  45     def decrypt(self, ciphertext):
  46         AES.decrypt(self, ciphertext)
  47
  48         ciphertextBytes = stringToBytes(ciphertext)
  49         chainBytes = stringToBytes(self.IV)
  50
  51         #CBC Mode: For each block...
  52         for x in range(len(ciphertextBytes)/16):
  53
  54             #Decrypt it
  55             blockBytes = ciphertextBytes[x*16 : (x*16)+16]
  56             blockString = bytesToString(blockBytes)
  57             decryptedBytes = stringToBytes(self.rijndael.decrypt(blockString))
  58
  59             #XOR with the chaining block and overwrite the input with output
  60             for y in range(16):
  61                 decryptedBytes[y] ^= chainBytes[y]
  62                 ciphertextBytes[(x*16)+y] = decryptedBytes[y]
  63
  64             #Set the next chaining block
  65             chainBytes = blockBytes
  66
  67         self.IV = bytesToString(chainBytes)
  68         return bytesToString(ciphertextBytes)