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89 lines
2.7 KiB
Python
89 lines
2.7 KiB
Python
"""
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AES IGE implementation in Python. This module may use libssl if available.
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"""
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import os
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import pyaes
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from . import libssl
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if libssl.AES is not None:
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# Use libssl if available, since it will be faster
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AES = libssl.AES
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else:
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# Fallback to a pure Python implementation
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class AES:
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"""
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Class that servers as an interface to encrypt and decrypt
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text through the AES IGE mode.
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"""
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@staticmethod
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def decrypt_ige(cipher_text, key, iv):
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"""
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Decrypts the given text in 16-bytes blocks by using the
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given key and 32-bytes initialization vector.
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"""
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iv1 = iv[:len(iv) // 2]
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iv2 = iv[len(iv) // 2:]
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aes = pyaes.AES(key)
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plain_text = []
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blocks_count = len(cipher_text) // 16
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cipher_text_block = [0] * 16
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for block_index in range(blocks_count):
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for i in range(16):
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cipher_text_block[i] = \
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cipher_text[block_index * 16 + i] ^ iv2[i]
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plain_text_block = aes.decrypt(cipher_text_block)
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for i in range(16):
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plain_text_block[i] ^= iv1[i]
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iv1 = cipher_text[block_index * 16:block_index * 16 + 16]
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iv2 = plain_text_block
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plain_text.extend(plain_text_block)
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return bytes(plain_text)
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@staticmethod
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def encrypt_ige(plain_text, key, iv):
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"""
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Encrypts the given text in 16-bytes blocks by using the
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given key and 32-bytes initialization vector.
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"""
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# Add random padding iff it's not evenly divisible by 16 already
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if len(plain_text) % 16 != 0:
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padding_count = 16 - len(plain_text) % 16
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plain_text += os.urandom(padding_count)
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iv1 = iv[:len(iv) // 2]
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iv2 = iv[len(iv) // 2:]
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aes = pyaes.AES(key)
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cipher_text = []
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blocks_count = len(plain_text) // 16
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for block_index in range(blocks_count):
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plain_text_block = list(
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plain_text[block_index * 16:block_index * 16 + 16]
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)
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for i in range(16):
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plain_text_block[i] ^= iv1[i]
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cipher_text_block = aes.encrypt(plain_text_block)
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for i in range(16):
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cipher_text_block[i] ^= iv2[i]
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iv1 = cipher_text_block
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iv2 = plain_text[block_index * 16:block_index * 16 + 16]
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cipher_text.extend(cipher_text_block)
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return bytes(cipher_text)
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