118 lines
3.6 KiB
Python
Executable File
118 lines
3.6 KiB
Python
Executable File
#!/usr/bin/env python
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from __future__ import print_function
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import base64
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import json
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import struct
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from cryptography.hazmat import backends
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from cryptography.hazmat.primitives import ciphers, hashes, hmac
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from cryptography.hazmat.primitives.kdf import pbkdf2
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from cryptography.hazmat.primitives.ciphers import algorithms, modes
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backend = backends.default_backend()
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def parse_u128(s):
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a, b = struct.unpack(">QQ", s)
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return (a << 64) | b
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def encrypt_ctr(key, iv, plaintext, counter_bits=64):
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alg = algorithms.AES(key)
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# Some AES-CTR implementations treat some parts of the IV as a nonce (which
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# remains constant throughought encryption), and some as a counter (which
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# increments every block, ie 16 bytes, and wraps after a while). Different
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# implmententations use different amounts of the IV for each part.
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#
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# The python cryptography library uses the whole IV as a counter; to make
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# it match other implementations with a given counter size, we manually
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# implement wrapping the counter.
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# number of AES blocks between each counter wrap
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limit = 1 << counter_bits
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# parse IV as a 128-bit int
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parsed_iv = parse_u128(iv)
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# split IV into counter and nonce
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counter = parsed_iv & (limit - 1)
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nonce = parsed_iv & ~(limit - 1)
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# encrypt up to the first counter wraparound
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size = 16 * (limit - counter)
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encryptor = ciphers.Cipher(
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alg,
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modes.CTR(iv),
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backend=backend
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).encryptor()
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input = plaintext[:size]
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result = encryptor.update(input) + encryptor.finalize()
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offset = size
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# do remaining data starting with a counter of zero
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iv = struct.pack(">QQ", nonce >> 64, nonce & ((1 << 64) - 1))
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size = 16 * limit
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while offset < len(plaintext):
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encryptor = ciphers.Cipher(
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alg,
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modes.CTR(iv),
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backend=backend
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).encryptor()
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input = plaintext[offset:offset+size]
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result += encryptor.update(input) + encryptor.finalize()
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offset += size
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return result
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def hmac_sha256(key, message):
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h = hmac.HMAC(key, hashes.SHA256(), backend=backend)
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h.update(message)
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return h.finalize()
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def encrypt(key, iv, salt, plaintext, iterations=1000):
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"""
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Returns:
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(bytes) ciphertext
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"""
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if len(salt) != 16:
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raise Exception("Expected 128 bits of salt - got %i bits" % len((salt) * 8))
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if len(iv) != 16:
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raise Exception("Expected 128 bits of IV - got %i bits" % (len(iv) * 8))
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sha = hashes.SHA512()
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kdf = pbkdf2.PBKDF2HMAC(sha, 64, salt, iterations, backend)
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k = kdf.derive(key)
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aes_key = k[0:32]
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sha_key = k[32:]
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packed_file = (
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b"\x01" # version
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+ salt
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+ iv
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+ struct.pack(">L", iterations)
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+ encrypt_ctr(aes_key, iv, plaintext)
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)
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packed_file += hmac_sha256(sha_key, packed_file)
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return (
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b"-----BEGIN MEGOLM SESSION DATA-----\n" +
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base64.encodestring(packed_file) +
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b"-----END MEGOLM SESSION DATA-----"
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)
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def gen(password, iv, salt, plaintext, iterations=1000):
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ciphertext = encrypt(
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password.encode('utf-8'), iv, salt, plaintext.encode('utf-8'), iterations
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)
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return (plaintext, password, ciphertext.decode('utf-8'))
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print (json.dumps([
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gen("password", b"\x88"*16, b"saltsaltsaltsalt", "plain", 10),
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gen("betterpassword", b"\xFF"*8 + b"\x00"*8, b"moresaltmoresalt", "Hello, World"),
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gen("SWORDFISH", b"\xFF"*8 + b"\x00"*8, b"yessaltygoodness", "alphanumerically" * 4),
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gen("password"*32, b"\xFF"*16, b"\xFF"*16, "alphanumerically" * 4),
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], indent=4))
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