diff options
Diffstat (limited to 'rsa/pkcs1.py')
-rw-r--r-- | rsa/pkcs1.py | 12 |
1 files changed, 8 insertions, 4 deletions
diff --git a/rsa/pkcs1.py b/rsa/pkcs1.py index 57b0276..19e24c7 100644 --- a/rsa/pkcs1.py +++ b/rsa/pkcs1.py @@ -30,6 +30,7 @@ import hashlib import os import sys import typing +from hmac import compare_digest from . import common, transform, core, key @@ -251,17 +252,20 @@ def decrypt(crypto: bytes, priv_key: key.PrivateKey) -> bytes: # Detect leading zeroes in the crypto. These are not reflected in the # encrypted value (as leading zeroes do not influence the value of an # integer). This fixes CVE-2020-13757. - if len(crypto) > blocksize: - raise DecryptionError('Decryption failed') + crypto_len_bad = len(crypto) > blocksize # If we can't find the cleartext marker, decryption failed. - if cleartext[0:2] != b'\x00\x02': - raise DecryptionError('Decryption failed') + cleartext_marker_bad = not compare_digest(cleartext[:2], b'\x00\x02') # Find the 00 separator between the padding and the message try: sep_idx = cleartext.index(b'\x00', 2) except ValueError: + sep_idx = -1 + sep_idx_bad = sep_idx < 0 + + anything_bad = crypto_len_bad | cleartext_marker_bad | sep_idx_bad + if anything_bad: raise DecryptionError('Decryption failed') return cleartext[sep_idx + 1:] |