Avoid changing signature of RSA._decrypt() method if possible

Author: Legrandin

lib/Crypto/Cipher/PKCS1_OAEP.py

@@ -168,7 +168,7 @@ def decrypt(self, ciphertext):
         # Step 2a (O2SIP)
         ct_int = bytes_to_long(ciphertext)
         # Step 2b (RSADP) and step 2c (I2OSP)
-        em = self._key._decrypt(ct_int)
+        em = self._key._decrypt_to_bytes(ct_int)
         # Step 3a
         lHash = self._hashObj.new(self._label).digest()
         # Step 3b

lib/Crypto/Cipher/PKCS1_v1_5.py

@@ -177,7 +177,7 @@ def decrypt(self, ciphertext, sentinel, expected_pt_len=0):
         ct_int = bytes_to_long(ciphertext)
 
         # Step 2b (RSADP) and Step 2c (I2OSP)
-        em = self._key._decrypt(ct_int)
+        em = self._key._decrypt_to_bytes(ct_int)
 
         # Step 3 (not constant time when the sentinel is not a byte string)
         output = bytes(bytearray(k))

lib/Crypto/PublicKey/RSA.py

@@ -181,7 +181,7 @@ def _encrypt(self, plaintext):
             raise ValueError("Plaintext too large")
         return int(pow(Integer(plaintext), self._e, self._n))
 
-    def _decrypt(self, ciphertext):
+    def _decrypt_to_bytes(self, ciphertext):
         if not 0 <= ciphertext < self._n:
             raise ValueError("Ciphertext too large")
         if not self.has_private():
@@ -206,6 +206,11 @@ def _decrypt(self, ciphertext):
                     self._n)
         return result
 
+    def _decrypt(self, ciphertext):
+        """Legacy private method"""
+
+        return bytes_to_long(self._decrypt_to_bytes(ciphertext))
+
     def has_private(self):
         """Whether this is an RSA private key"""
 

lib/Crypto/SelfTest/PublicKey/test_RSA.py

@@ -214,9 +214,11 @@ def test_raw_rsa_boundary(self):
         rsa_obj = self.rsa.generate(1024)
 
         self.assertRaises(ValueError, rsa_obj._decrypt, rsa_obj.n)
+        self.assertRaises(ValueError, rsa_obj._decrypt_to_bytes, rsa_obj.n)
         self.assertRaises(ValueError, rsa_obj._encrypt, rsa_obj.n)
 
         self.assertRaises(ValueError, rsa_obj._decrypt, -1)
+        self.assertRaises(ValueError, rsa_obj._decrypt_to_bytes, -1)
         self.assertRaises(ValueError, rsa_obj._encrypt, -1)
 
     def test_size(self):
@@ -265,6 +267,8 @@ def _check_public_key(self, rsaObj):
         # Public keys should not be able to sign or decrypt
         self.assertRaises(TypeError, rsaObj._decrypt,
                 bytes_to_long(ciphertext))
+        self.assertRaises(TypeError, rsaObj._decrypt_to_bytes,
+                bytes_to_long(ciphertext))
 
         # Check __eq__ and __ne__
         self.assertEqual(rsaObj.public_key() == rsaObj.public_key(),True) # assert_
@@ -279,7 +283,7 @@ def _exercise_primitive(self, rsaObj):
         ciphertext = bytes_to_long(a2b_hex(self.ciphertext))
 
         # Test decryption
-        plaintext = bytes_to_long(rsaObj._decrypt(ciphertext))
+        plaintext = rsaObj._decrypt(ciphertext)
 
         # Test encryption (2 arguments)
         new_ciphertext2 = rsaObj._encrypt(plaintext)
@@ -304,7 +308,7 @@ def _check_decryption(self, rsaObj):
         ciphertext = bytes_to_long(a2b_hex(self.ciphertext))
 
         # Test plain decryption
-        new_plaintext = bytes_to_long(rsaObj._decrypt(ciphertext))
+        new_plaintext = rsaObj._decrypt(ciphertext)
         self.assertEqual(plaintext, new_plaintext)
 
 

lib/Crypto/SelfTest/PublicKey/test_import_RSA.py

@@ -239,13 +239,13 @@ def testImportKey4bytes(self):
     def testImportKey5(self):
         """Verifies that the imported key is still a valid RSA pair"""
         key = RSA.importKey(self.rsaKeyPEM)
-        idem = key._encrypt(bytes_to_long(key._decrypt(89)))
+        idem = key._encrypt(key._decrypt(89))
         self.assertEqual(idem, 89)
 
     def testImportKey6(self):
         """Verifies that the imported key is still a valid RSA pair"""
         key = RSA.importKey(self.rsaKeyDER)
-        idem = key._encrypt(bytes_to_long(key._decrypt(65)))
+        idem = key._encrypt(key._decrypt(65))
         self.assertEqual(idem, 65)
 
     def testImportKey7(self):

lib/Crypto/Signature/pkcs1_15.py

@@ -78,7 +78,7 @@ def sign(self, msg_hash):
         # Step 2a (OS2IP)
         em_int = bytes_to_long(em)
         # Step 2b (RSASP1) and Step 2c (I2OSP)
-        signature = self._key._decrypt(em_int)
+        signature = self._key._decrypt_to_bytes(em_int)
         # Verify no faults occurred
         if em_int != pow(bytes_to_long(signature), self._key.e, self._key.n):
             raise ValueError("Fault detected in RSA private key operation")

lib/Crypto/Signature/pss.py

@@ -108,7 +108,7 @@ def sign(self, msg_hash):
         # Step 2a (OS2IP)
         em_int = bytes_to_long(em)
         # Step 2b (RSASP1) and Step 2c (I2OSP)
-        signature = self._key._decrypt(em_int)
+        signature = self._key._decrypt_to_bytes(em_int)
         # Verify no faults occurred
         if em_int != pow(bytes_to_long(signature), self._key.e, self._key.n):
             raise ValueError("Fault detected in RSA private key operation")