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Diffstat (limited to 'lib/Python/Lib/Crypto/Cipher/PKCS1_v1_5.py')
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diff --git a/lib/Python/Lib/Crypto/Cipher/PKCS1_v1_5.py b/lib/Python/Lib/Crypto/Cipher/PKCS1_v1_5.py new file mode 100644 index 000000000..c89035d79 --- /dev/null +++ b/lib/Python/Lib/Crypto/Cipher/PKCS1_v1_5.py @@ -0,0 +1,226 @@ +# -*- coding: utf-8 -*- +# +# Cipher/PKCS1-v1_5.py : PKCS#1 v1.5 +# +# =================================================================== +# The contents of this file are dedicated to the public domain. To +# the extent that dedication to the public domain is not available, +# everyone is granted a worldwide, perpetual, royalty-free, +# non-exclusive license to exercise all rights associated with the +# contents of this file for any purpose whatsoever. +# No rights are reserved. +# +# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, +# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF +# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND +# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS +# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN +# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN +# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE +# SOFTWARE. +# =================================================================== + +"""RSA encryption protocol according to PKCS#1 v1.5 + +See RFC3447__ or the `original RSA Labs specification`__ . + +This scheme is more properly called ``RSAES-PKCS1-v1_5``. + +**If you are designing a new protocol, consider using the more robust PKCS#1 OAEP.** + +As an example, a sender may encrypt a message in this way: + + >>> from Crypto.Cipher import PKCS1_v1_5 + >>> from Crypto.PublicKey import RSA + >>> from Crypto.Hash import SHA + >>> + >>> message = 'To be encrypted' + >>> h = SHA.new(message) + >>> + >>> key = RSA.importKey(open('pubkey.der').read()) + >>> cipher = PKCS1_v1_5.new(key) + >>> ciphertext = cipher.encrypt(message+h.digest()) + +At the receiver side, decryption can be done using the private part of +the RSA key: + + >>> From Crypto.Hash import SHA + >>> from Crypto import Random + >>> + >>> key = RSA.importKey(open('privkey.der').read()) + >>> + >>> dsize = SHA.digest_size + >>> sentinel = Random.new().read(15+dsize) # Let's assume that average data length is 15 + >>> + >>> cipher = PKCS1_v1_5.new(key) + >>> message = cipher.decrypt(ciphertext, sentinel) + >>> + >>> digest = SHA.new(message[:-dsize]).digest() + >>> if digest==message[-dsize:]: # Note how we DO NOT look for the sentinel + >>> print "Encryption was correct." + >>> else: + >>> print "Encryption was not correct." + +:undocumented: __revision__, __package__ + +.. __: http://www.ietf.org/rfc/rfc3447.txt +.. __: http://www.rsa.com/rsalabs/node.asp?id=2125. +""" + +__revision__ = "$Id$" +__all__ = [ 'new', 'PKCS115_Cipher' ] + +from Crypto.Util.number import ceil_div +from Crypto.Util.py3compat import * +import Crypto.Util.number + +class PKCS115_Cipher: + """This cipher can perform PKCS#1 v1.5 RSA encryption or decryption.""" + + def __init__(self, key): + """Initialize this PKCS#1 v1.5 cipher object. + + :Parameters: + key : an RSA key object + If a private half is given, both encryption and decryption are possible. + If a public half is given, only encryption is possible. + """ + self._key = key + + def can_encrypt(self): + """Return True if this cipher object can be used for encryption.""" + return self._key.can_encrypt() + + def can_decrypt(self): + """Return True if this cipher object can be used for decryption.""" + return self._key.can_decrypt() + + def encrypt(self, message): + """Produce the PKCS#1 v1.5 encryption of a message. + + This function is named ``RSAES-PKCS1-V1_5-ENCRYPT``, and is specified in + section 7.2.1 of RFC3447. + For a complete example see `Crypto.Cipher.PKCS1_v1_5`. + + :Parameters: + message : byte string + The message to encrypt, also known as plaintext. It can be of + variable length, but not longer than the RSA modulus (in bytes) minus 11. + + :Return: A byte string, the ciphertext in which the message is encrypted. + It is as long as the RSA modulus (in bytes). + :Raise ValueError: + If the RSA key length is not sufficiently long to deal with the given + message. + + """ + # TODO: Verify the key is RSA + + randFunc = self._key._randfunc + + # See 7.2.1 in RFC3447 + modBits = Crypto.Util.number.size(self._key.n) + k = ceil_div(modBits,8) # Convert from bits to bytes + mLen = len(message) + + # Step 1 + if mLen > k-11: + raise ValueError("Plaintext is too long.") + # Step 2a + class nonZeroRandByte: + def __init__(self, rf): self.rf=rf + def __call__(self, c): + while bord(c)==0x00: c=self.rf(1)[0] + return c + ps = tobytes(map(nonZeroRandByte(randFunc), randFunc(k-mLen-3))) + # Step 2b + em = b('\x00\x02') + ps + bchr(0x00) + message + # Step 3a (OS2IP), step 3b (RSAEP), part of step 3c (I2OSP) + m = self._key.encrypt(em, 0)[0] + # Complete step 3c (I2OSP) + c = bchr(0x00)*(k-len(m)) + m + return c + + def decrypt(self, ct, sentinel): + """Decrypt a PKCS#1 v1.5 ciphertext. + + This function is named ``RSAES-PKCS1-V1_5-DECRYPT``, and is specified in + section 7.2.2 of RFC3447. + For a complete example see `Crypto.Cipher.PKCS1_v1_5`. + + :Parameters: + ct : byte string + The ciphertext that contains the message to recover. + sentinel : any type + The object to return to indicate that an error was detected during decryption. + + :Return: A byte string. It is either the original message or the ``sentinel`` (in case of an error). + :Raise ValueError: + If the ciphertext length is incorrect + :Raise TypeError: + If the RSA key has no private half. + + :attention: + You should **never** let the party who submitted the ciphertext know that + this function returned the ``sentinel`` value. + Armed with such knowledge (for a fair amount of carefully crafted but invalid ciphertexts), + an attacker is able to recontruct the plaintext of any other encryption that were carried out + with the same RSA public key (see `Bleichenbacher's`__ attack). + + In general, it should not be possible for the other party to distinguish + whether processing at the server side failed because the value returned + was a ``sentinel`` as opposed to a random, invalid message. + + In fact, the second option is not that unlikely: encryption done according to PKCS#1 v1.5 + embeds no good integrity check. There is roughly one chance + in 2^16 for a random ciphertext to be returned as a valid message + (although random looking). + + It is therefore advisabled to: + + 1. Select as ``sentinel`` a value that resembles a plausable random, invalid message. + 2. Not report back an error as soon as you detect a ``sentinel`` value. + Put differently, you should not explicitly check if the returned value is the ``sentinel`` or not. + 3. Cover all possible errors with a single, generic error indicator. + 4. Embed into the definition of ``message`` (at the protocol level) a digest (e.g. ``SHA-1``). + It is recommended for it to be the rightmost part ``message``. + 5. Where possible, monitor the number of errors due to ciphertexts originating from the same party, + and slow down the rate of the requests from such party (or even blacklist it altogether). + + **If you are designing a new protocol, consider using the more robust PKCS#1 OAEP.** + + .. __: http://www.bell-labs.com/user/bleichen/papers/pkcs.ps + + """ + + # TODO: Verify the key is RSA + + # See 7.2.1 in RFC3447 + modBits = Crypto.Util.number.size(self._key.n) + k = ceil_div(modBits,8) # Convert from bits to bytes + + # Step 1 + if len(ct) != k: + raise ValueError("Ciphertext with incorrect length.") + # Step 2a (O2SIP), 2b (RSADP), and part of 2c (I2OSP) + m = self._key.decrypt(ct) + # Complete step 2c (I2OSP) + em = bchr(0x00)*(k-len(m)) + m + # Step 3 + sep = em.find(bchr(0x00),2) + if not em.startswith(b('\x00\x02')) or sep<10: + return sentinel + # Step 4 + return em[sep+1:] + +def new(key): + """Return a cipher object `PKCS115_Cipher` that can be used to perform PKCS#1 v1.5 encryption or decryption. + + :Parameters: + key : RSA key object + The key to use to encrypt or decrypt the message. This is a `Crypto.PublicKey.RSA` object. + Decryption is only possible if *key* is a private RSA key. + + """ + return PKCS115_Cipher(key) + |