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Fix v1 login by calculating public exp instead of hardcode 257.

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The code was using a hardcoded 257 as the RSA public exponent, but
it was raising RSA Invalid Construct. From reading MEGA's webclient js
I found that the public exponent sometimes defaults to 257, but in
other cases is calculated from a modular inverse on the private
exponent and phi=p-1*q-1.
This commit is contained in:
Ethan Dalool 2020-03-09 15:13:12 -07:00
parent f1047898e8
commit 1e96d9b435
1 changed files with 22 additions and 8 deletions
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30
src/mega/mega.py
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@ -21,7 +21,8 @@ from .errors import ValidationError, RequestError
from .crypto import (
a32_to_base64, encrypt_key, base64_url_encode, encrypt_attr, base64_to_a32,
base64_url_decode, decrypt_attr, a32_to_str, get_chunks, str_to_a32,
decrypt_key, mpi_to_int, stringhash, prepare_key, make_id, makebyte
decrypt_key, mpi_to_int, stringhash, prepare_key, make_id, makebyte,
modular_inverse
)
logger = logging.getLogger(__name__)
@ -132,14 +133,27 @@ class Mega:
rsa_private_key[i] = mpi_to_int(private_key[:bytelength])
private_key = private_key[bytelength:]
encrypted_sid = mpi_to_int(base64_url_decode(resp['csid']))
rsa_decrypter = RSA.construct(
(
rsa_private_key[0] * rsa_private_key[1], 257,
rsa_private_key[2], rsa_private_key[0],
rsa_private_key[1]
)
first_factor_p = rsa_private_key[0]
second_factor_q = rsa_private_key[1]
private_exponent_d = rsa_private_key[2]
# In MEGA's webclient javascript, they assign [3] to a variable
# called u, but I do not see how it corresponds to pycryptodome's
# RSA.construct and it does not seem to be necessary.
rsa_modulus_n = first_factor_p * second_factor_q
phi = (first_factor_p - 1) * (second_factor_q - 1)
public_exponent_e = modular_inverse(private_exponent_d, phi)
rsa_components = (
rsa_modulus_n,
public_exponent_e,
private_exponent_d,
first_factor_p,
second_factor_q,
)
rsa_decrypter = RSA.construct(rsa_components)
encrypted_sid = mpi_to_int(base64_url_decode(resp['csid']))
sid = '%x' % rsa_decrypter._decrypt(encrypted_sid)
sid = binascii.unhexlify('0' + sid if len(sid) % 2 else sid)
self.sid = base64_url_encode(sid[:43])