From 8dbe0dc3eea5c689d4f76b37b93fe216cf1f00d4 Mon Sep 17 00:00:00 2001 From: Legrandin Date: Sun, 22 Dec 2013 22:24:46 +0100 Subject: [PATCH] Throw exception when IV is used with ECB or CTR The IV parameter is currently ignored when initializing a cipher in ECB or CTR mode. For CTR mode, it is confusing: it takes some time to see that a different parameter is needed (the counter). For ECB mode, it is outright dangerous. This patch forces an exception to be raised. --- lib/Crypto/SelfTest/Cipher/common.py | 31 +++++++++++++++++++++++-------- src/block_template.c | 11 +++++++++++ 2 files changed, 34 insertions(+), 8 deletions(-) diff --git a/lib/Crypto/SelfTest/Cipher/common.py b/lib/Crypto/SelfTest/Cipher/common.py index 420b6ff..a5f8a88 100644 --- a/lib/Crypto/SelfTest/Cipher/common.py +++ b/lib/Crypto/SelfTest/Cipher/common.py @@ -239,19 +239,34 @@ def shortDescription(self): return """%s .decrypt() output of .encrypt() should not be garbled""" % (self.module_name,) def runTest(self): - for mode in (self.module.MODE_ECB, self.module.MODE_CBC, self.module.MODE_CFB, self.module.MODE_OFB, self.module.MODE_OPENPGP): + + ## ECB mode + mode = self.module.MODE_ECB + encryption_cipher = self.module.new(a2b_hex(self.key), mode) + ciphertext = encryption_cipher.encrypt(self.plaintext) + decryption_cipher = self.module.new(a2b_hex(self.key), mode) + decrypted_plaintext = decryption_cipher.decrypt(ciphertext) + self.assertEqual(self.plaintext, decrypted_plaintext) + + ## OPENPGP mode + mode = self.module.MODE_OPENPGP + encryption_cipher = self.module.new(a2b_hex(self.key), mode, self.iv) + eiv_ciphertext = encryption_cipher.encrypt(self.plaintext) + eiv = eiv_ciphertext[:self.module.block_size+2] + ciphertext = eiv_ciphertext[self.module.block_size+2:] + decryption_cipher = self.module.new(a2b_hex(self.key), mode, eiv) + decrypted_plaintext = decryption_cipher.decrypt(ciphertext) + self.assertEqual(self.plaintext, decrypted_plaintext) + + ## All other non-AEAD modes (but CTR) + for mode in (self.module.MODE_CBC, self.module.MODE_CFB, self.module.MODE_OFB): encryption_cipher = self.module.new(a2b_hex(self.key), mode, self.iv) ciphertext = encryption_cipher.encrypt(self.plaintext) - - if mode != self.module.MODE_OPENPGP: - decryption_cipher = self.module.new(a2b_hex(self.key), mode, self.iv) - else: - eiv = ciphertext[:self.module.block_size+2] - ciphertext = ciphertext[self.module.block_size+2:] - decryption_cipher = self.module.new(a2b_hex(self.key), mode, eiv) + decryption_cipher = self.module.new(a2b_hex(self.key), mode, self.iv) decrypted_plaintext = decryption_cipher.decrypt(ciphertext) self.assertEqual(self.plaintext, decrypted_plaintext) + class PGPTest(unittest.TestCase): def __init__(self, module, params): unittest.TestCase.__init__(self) diff --git a/src/block_template.c b/src/block_template.c index f940e0e..d555ceb 100644 --- a/src/block_template.c +++ b/src/block_template.c @@ -170,6 +170,17 @@ ALGnew(PyObject *self, PyObject *args, PyObject *kwdict) "Key cannot be the null string"); return NULL; } + if (IVlen != 0 && mode == MODE_ECB) + { + PyErr_Format(PyExc_ValueError, "ECB mode does not use IV"); + return NULL; + } + if (IVlen != 0 && mode == MODE_CTR) + { + PyErr_Format(PyExc_ValueError, + "CTR mode needs counter parameter, not IV"); + return NULL; + } if (IVlen != BLOCK_SIZE && mode != MODE_ECB && mode != MODE_CTR) { PyErr_Format(PyExc_ValueError,