From d8671b9d0943fd6e42365a04880724c2ff864a46 Mon Sep 17 00:00:00 2001
From: Helder Eijs <helderijs@gmail.com>
Date: Fri, 3 Dec 2021 22:12:42 +0100
Subject: [PATCH] GH#582 Fix incorrect CBC decryption when in/out use the same
 buffer

---
 lib/Crypto/SelfTest/Cipher/common.py   |  4 +---
 lib/Crypto/SelfTest/Cipher/test_CBC.py | 28 +++++++++++++-------------
 src/raw_cbc.c                          |  3 ++-
 3 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/lib/Crypto/SelfTest/Cipher/common.py b/lib/Crypto/SelfTest/Cipher/common.py
index 4ba2c33a9..c5bc755ab 100644
--- a/lib/Crypto/SelfTest/Cipher/common.py
+++ b/lib/Crypto/SelfTest/Cipher/common.py
@@ -499,9 +499,7 @@ def make_stream_tests(module, module_name, test_data):
                 ByteArrayTest(module, params),
             ]
 
-            import sys
-            if sys.version[:3] != '2.6':
-                tests.append(MemoryviewTest(module, params))
+            tests.append(MemoryviewTest(module, params))
             extra_tests_added = True
 
         # Add the test to the test suite
diff --git a/lib/Crypto/SelfTest/Cipher/test_CBC.py b/lib/Crypto/SelfTest/Cipher/test_CBC.py
index 13c32838c..573808fd1 100644
--- a/lib/Crypto/SelfTest/Cipher/test_CBC.py
+++ b/lib/Crypto/SelfTest/Cipher/test_CBC.py
@@ -168,7 +168,7 @@ def test_data_must_be_bytes(self):
         self.assertRaises(TypeError, cipher.decrypt, u'test1234567890-*')
 
     def test_bytearray(self):
-        data = b"1" * 16
+        data = b"1" * 128
         data_ba = bytearray(data)
 
         # Encrypt
@@ -201,7 +201,7 @@ def test_bytearray(self):
         self.assertEqual(ref3, ref4)
 
     def test_memoryview(self):
-        data = b"1" * 16
+        data = b"1" * 128
         data_mv = memoryview(bytearray(data))
 
         # Encrypt
@@ -232,19 +232,19 @@ def test_memoryview(self):
         ref4 = cipher4.decrypt(data_mv)
 
         self.assertEqual(ref3, ref4)
-    
+
     def test_output_param(self):
 
-        pt = b'5' * 16
+        pt = b'5' * 128
         cipher = AES.new(b'4'*16, self.aes_mode, iv=self.iv_128)
         ct = cipher.encrypt(pt)
 
-        output = bytearray(16)
+        output = bytearray(128)
         cipher = AES.new(b'4'*16, self.aes_mode, iv=self.iv_128)
         res = cipher.encrypt(pt, output=output)
         self.assertEqual(ct, output)
         self.assertEqual(res, None)
-        
+
         cipher = AES.new(b'4'*16, self.aes_mode, iv=self.iv_128)
         res = cipher.decrypt(ct, output=output)
         self.assertEqual(pt, output)
@@ -253,7 +253,7 @@ def test_output_param(self):
 
     def test_output_param_same_buffer(self):
 
-        pt = b'5' * 16
+        pt = b'5' * 128
         cipher = AES.new(b'4'*16, self.aes_mode, iv=self.iv_128)
         ct = cipher.encrypt(pt)
 
@@ -262,7 +262,7 @@ def test_output_param_same_buffer(self):
         res = cipher.encrypt(pt_ba, output=pt_ba)
         self.assertEqual(ct, pt_ba)
         self.assertEqual(res, None)
-        
+
         ct_ba = bytearray(ct)
         cipher = AES.new(b'4'*16, self.aes_mode, iv=self.iv_128)
         res = cipher.decrypt(ct_ba, output=ct_ba)
@@ -271,29 +271,29 @@ def test_output_param_same_buffer(self):
 
 
     def test_output_param_memoryview(self):
-        
-        pt = b'5' * 16
+
+        pt = b'5' * 128
         cipher = AES.new(b'4'*16, self.aes_mode, iv=self.iv_128)
         ct = cipher.encrypt(pt)
 
-        output = memoryview(bytearray(16))
+        output = memoryview(bytearray(128))
         cipher = AES.new(b'4'*16, self.aes_mode, iv=self.iv_128)
         cipher.encrypt(pt, output=output)
         self.assertEqual(ct, output)
-        
+
         cipher = AES.new(b'4'*16, self.aes_mode, iv=self.iv_128)
         cipher.decrypt(ct, output=output)
         self.assertEqual(pt, output)
 
     def test_output_param_neg(self):
 
-        pt = b'5' * 16
+        pt = b'5' * 128
         cipher = AES.new(b'4'*16, self.aes_mode, iv=self.iv_128)
         ct = cipher.encrypt(pt)
 
         cipher = AES.new(b'4'*16, self.aes_mode, iv=self.iv_128)
         self.assertRaises(TypeError, cipher.encrypt, pt, output=b'0'*16)
-        
+
         cipher = AES.new(b'4'*16, self.aes_mode, iv=self.iv_128)
         self.assertRaises(TypeError, cipher.decrypt, ct, output=b'0'*16)
 
diff --git a/src/raw_cbc.c b/src/raw_cbc.c
index a8a6b6dc8..36e5247db 100644
--- a/src/raw_cbc.c
+++ b/src/raw_cbc.c
@@ -137,9 +137,10 @@ EXPORT_SYM int CBC_decrypt(CbcModeState *cbcState,
             return result;
 
         for (i=0; i<block_len; i++)
-            out[i] = pt[i] ^ iv[i];
+            pt[i] = pt[i] ^ iv[i];
 
         memcpy(iv, in, block_len);
+        memcpy(out, pt, block_len);
 
         data_len -= block_len;
         in += block_len;