!6 fix CVE-2020-13757

Merge pull request !6 from Markeryang/master

0001-Fix-CVE-2020-13757.patch

@@ -0,0 +1,48 @@
+From 93af6f2f89a9bf28361e67716c4240e691520f30 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Sybren=20A=2E=20St=C3=BCvel?= <sybren@stuvel.eu>
+Date: Wed, 3 Jun 2020 14:39:23 +0200
+Subject: [PATCH] Fix CVE-2020-13757: detect cyphertext modifications by
+ prepending zero bytes
+
+Reject cyphertexts that have been modified by prepending zero bytes, by
+checking the cyphertext length against the expected size (given the
+decryption key). This resolves CVE-2020-13757.
+
+The same approach is used when verifying a signature.
+
+Thanks Carnil for pointing this out on https://github.com/sybrenstuvel/python-rsa/issues/146
+---
+ rsa/pkcs1.py        |  9 +++++++++
+ 1 files changed, 9 insertions(+)
+
+diff --git a/rsa/pkcs1.py b/rsa/pkcs1.py
+index 28f0dc5..cdf830b 100644
+--- a/rsa/pkcs1.py
++++ b/rsa/pkcs1.py
+@@ -232,6 +232,12 @@ 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')
+@@ -310,6 +316,9 @@ 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')
+ 
+-- 
+1.8.3.1
+

python-rsa.spec

@@ -1,12 +1,14 @@
 Name:           python-rsa
 Version:        3.4.2
-Release:        11
+Release:        12
 Summary:        Pure-Python RSA implementation
 License:        ASL 2.0
 URL:            http://stuvel.eu/rsa
 Source0:        https://pypi.python.org/packages/source/r/rsa/rsa-%{version}.tar.gz
 BuildArch:      noarch
 
+Patch1: 0001-Fix-CVE-2020-13757.patch
+
 %description
 Python-RSA is a pure-Python RSA implementation. It supports
 encryption and decryption, signing and verifying signatures,
@@ -79,5 +81,8 @@ mv $RPM_BUILD_ROOT%{_bindir}/pyrsa-decrypt-bigfile $RPM_BUILD_ROOT%{_bindir}/pyr
 %{__python3} setup.py test
 
 %changelog
+* Tue Aug 4 2020 yanglongkang <yanglongkang@huawei.com> - 3.4.2-12
+- fix CVE-2020-13757
+
 * Mon Feb 10 2020 Ruijun Ge <geruijun@huawei.com> - 3.4.2-11
 - package init