diff options
| -rw-r--r-- | CHANGELOG.txt | 3 | ||||
| -rw-r--r-- | rsa/pkcs1.py | 9 | ||||
| -rw-r--r-- | tests/test_pkcs1.py | 50 |
3 files changed, 62 insertions, 0 deletions
diff --git a/CHANGELOG.txt b/CHANGELOG.txt index 2704e69..96a380d 100644 --- a/CHANGELOG.txt +++ b/CHANGELOG.txt @@ -11,6 +11,9 @@ in `setup.py`. Two security fixes have also been backported, so 4.3 = 4.0 + these two fixes. - Choose blinding factor relatively prime to N. Thanks Christian Heimes for pointing this out. +- Reject cyphertexts (when decrypting) and signatures (when verifying) that have + been modified by prepending zero bytes. This resolves CVE-2020-13757. Thanks + Carnil for pointing this out. Version 4.0 - released 2018-09-16 diff --git a/rsa/pkcs1.py b/rsa/pkcs1.py index 84f0e3b..c05239a 100644 --- a/rsa/pkcs1.py +++ b/rsa/pkcs1.py @@ -234,6 +234,12 @@ def decrypt(crypto, priv_key): decrypted = priv_key.blinded_decrypt(encrypted) cleartext = transform.int2bytes(decrypted, blocksize) + # 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') + # If we can't find the cleartext marker, decryption failed. if cleartext[0:2] != b'\x00\x02': raise DecryptionError('Decryption failed') @@ -331,6 +337,9 @@ def verify(message, signature, pub_key): cleartext = HASH_ASN1[method_name] + message_hash expected = _pad_for_signing(cleartext, keylength) + if len(signature) != keylength: + raise VerificationError('Verification failed') + # Compare with the signed one if expected != clearsig: raise VerificationError('Verification failed') diff --git a/tests/test_pkcs1.py b/tests/test_pkcs1.py index 5377b30..9f7dcea 100644 --- a/tests/test_pkcs1.py +++ b/tests/test_pkcs1.py @@ -17,6 +17,7 @@ """Tests string operations.""" import struct +import sys import unittest import rsa @@ -66,6 +67,37 @@ class BinaryTest(unittest.TestCase): self.assertNotEqual(encrypted1, encrypted2) +class ExtraZeroesTest(unittest.TestCase): + def setUp(self): + # Key, cyphertext, and plaintext taken from https://github.com/sybrenstuvel/python-rsa/issues/146 + self.private_key = rsa.PrivateKey.load_pkcs1( + "-----BEGIN RSA PRIVATE KEY-----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\nXVJl32HuKYPJOMIWfc7hIfxLRHnCN+coz2M6tgqMDs0E/OfjuqVZ\n-----END RSA PRIVATE KEY-----", + format='PEM') + cyphertext = "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" + plaintext = "54657374" + + if sys.version_info < (3, 0): + self.cyphertext = cyphertext.decode("hex") + self.plaintext = plaintext.decode('hex') + else: + self.cyphertext = bytes.fromhex(cyphertext) + self.plaintext = bytes.fromhex(plaintext) + + def test_unmodified(self): + message = rsa.decrypt(self.cyphertext, self.private_key) + self.assertEqual(message, self.plaintext) + + def test_prepend_zeroes(self): + cyphertext = b'\00\00' + self.cyphertext + with self.assertRaises(rsa.DecryptionError): + rsa.decrypt(cyphertext, self.private_key) + + def test_append_zeroes(self): + cyphertext = self.cyphertext + b'\00\00' + with self.assertRaises(rsa.DecryptionError): + rsa.decrypt(cyphertext, self.private_key) + + class SignatureTest(unittest.TestCase): def setUp(self): (self.pub, self.priv) = rsa.newkeys(512) @@ -132,3 +164,21 @@ class SignatureTest(unittest.TestCase): signature = pkcs1.sign_hash(msg_hash, self.priv, 'SHA-224') self.assertTrue(pkcs1.verify(message, signature, self.pub)) + + def test_prepend_zeroes(self): + """Prepending the signature with zeroes should be detected.""" + + message = b'je moeder' + signature = pkcs1.sign(message, self.priv, 'SHA-256') + signature = b'\00\00' + signature + with self.assertRaises(rsa.VerificationError): + pkcs1.verify(message, signature, self.pub) + + def test_apppend_zeroes(self): + """Apppending the signature with zeroes should be detected.""" + + message = b'je moeder' + signature = pkcs1.sign(message, self.priv, 'SHA-256') + signature = signature + b'\00\00' + with self.assertRaises(rsa.VerificationError): + pkcs1.verify(message, signature, self.pub) |