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")