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Diffstat (limited to 'lib/Python/Lib/Crypto/Cipher/PKCS1_OAEP.py')
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diff --git a/lib/Python/Lib/Crypto/Cipher/PKCS1_OAEP.py b/lib/Python/Lib/Crypto/Cipher/PKCS1_OAEP.py new file mode 100644 index 000000000..9afe176f1 --- /dev/null +++ b/lib/Python/Lib/Crypto/Cipher/PKCS1_OAEP.py @@ -0,0 +1,255 @@ +# -*- coding: utf-8 -*- +# +# Cipher/PKCS1_OAEP.py : PKCS#1 OAEP +# +# =================================================================== +# 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 OAEP + +See RFC3447__ or the `original RSA Labs specification`__ . + +This scheme is more properly called ``RSAES-OAEP``. + +As an example, a sender may encrypt a message in this way: + + >>> from Crypto.Cipher import PKCS1_OAEP + >>> from Crypto.PublicKey import RSA + >>> + >>> message = 'To be encrypted' + >>> key = RSA.importKey(open('pubkey.der').read()) + >>> cipher = PKCS1_OAEP.new(key) + >>> ciphertext = cipher.encrypt(message) + +At the receiver side, decryption can be done using the private part of +the RSA key: + + >>> key = RSA.importKey(open('privkey.der').read()) + >>> cipher = PKCS1_OAP.new(key) + >>> message = cipher.decrypt(ciphertext) + +:undocumented: __revision__, __package__ + +.. __: http://www.ietf.org/rfc/rfc3447.txt +.. __: http://www.rsa.com/rsalabs/node.asp?id=2125. +""" + +from __future__ import nested_scopes + +__revision__ = "$Id$" +__all__ = [ 'new', 'PKCS1OAEP_Cipher' ] + +import Crypto.Signature.PKCS1_PSS +import Crypto.Hash.SHA + +from Crypto.Util.py3compat import * +import Crypto.Util.number +from Crypto.Util.number import ceil_div +from Crypto.Util.strxor import strxor + +class PKCS1OAEP_Cipher: + """This cipher can perform PKCS#1 v1.5 OAEP encryption or decryption.""" + + def __init__(self, key, hashAlgo, mgfunc, label): + """Initialize this PKCS#1 OAEP 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. + hashAlgo : hash object + The hash function to use. This can be a module under `Crypto.Hash` + or an existing hash object created from any of such modules. If not specified, + `Crypto.Hash.SHA` (that is, SHA-1) is used. + mgfunc : callable + A mask generation function that accepts two parameters: a string to + use as seed, and the lenth of the mask to generate, in bytes. + If not specified, the standard MGF1 is used (a safe choice). + label : string + A label to apply to this particular encryption. If not specified, + an empty string is used. Specifying a label does not improve + security. + + :attention: Modify the mask generation function only if you know what you are doing. + Sender and receiver must use the same one. + """ + self._key = key + + if hashAlgo: + self._hashObj = hashAlgo + else: + self._hashObj = Crypto.Hash.SHA + + if mgfunc: + self._mgf = mgfunc + else: + self._mgf = lambda x,y: Crypto.Signature.PKCS1_PSS.MGF1(x,y,self._hashObj) + + self._label = label + + def can_encrypt(self): + """Return True/1 if this cipher object can be used for encryption.""" + return self._key.can_encrypt() + + def can_decrypt(self): + """Return True/1 if this cipher object can be used for decryption.""" + return self._key.can_decrypt() + + def encrypt(self, message): + """Produce the PKCS#1 OAEP encryption of a message. + + This function is named ``RSAES-OAEP-ENCRYPT``, and is specified in + section 7.1.1 of RFC3447. + + :Parameters: + message : 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 2, minus twice the hash output size. + + :Return: A 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 7.1.1 in RFC3447 + modBits = Crypto.Util.number.size(self._key.n) + k = ceil_div(modBits,8) # Convert from bits to bytes + hLen = self._hashObj.digest_size + mLen = len(message) + + # Step 1b + ps_len = k-mLen-2*hLen-2 + if ps_len<0: + raise ValueError("Plaintext is too long.") + # Step 2a + lHash = self._hashObj.new(self._label).digest() + # Step 2b + ps = bchr(0x00)*ps_len + # Step 2c + db = lHash + ps + bchr(0x01) + message + # Step 2d + ros = randFunc(hLen) + # Step 2e + dbMask = self._mgf(ros, k-hLen-1) + # Step 2f + maskedDB = strxor(db, dbMask) + # Step 2g + seedMask = self._mgf(maskedDB, hLen) + # Step 2h + maskedSeed = strxor(ros, seedMask) + # Step 2i + em = bchr(0x00) + maskedSeed + maskedDB + # 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): + """Decrypt a PKCS#1 OAEP ciphertext. + + This function is named ``RSAES-OAEP-DECRYPT``, and is specified in + section 7.1.2 of RFC3447. + + :Parameters: + ct : string + The ciphertext that contains the message to recover. + + :Return: A string, the original message. + :Raise ValueError: + If the ciphertext length is incorrect, or if the decryption does not + succeed. + :Raise TypeError: + If the RSA key has no private half. + """ + # TODO: Verify the key is RSA + + # See 7.1.2 in RFC3447 + modBits = Crypto.Util.number.size(self._key.n) + k = ceil_div(modBits,8) # Convert from bits to bytes + hLen = self._hashObj.digest_size + + # Step 1b and 1c + if len(ct) != k or k<hLen+2: + 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 3a + lHash = self._hashObj.new(self._label).digest() + # Step 3b + y = em[0] + # y must be 0, but we MUST NOT check it here in order not to + # allow attacks like Manger's (http://dl.acm.org/citation.cfm?id=704143) + maskedSeed = em[1:hLen+1] + maskedDB = em[hLen+1:] + # Step 3c + seedMask = self._mgf(maskedDB, hLen) + # Step 3d + seed = strxor(maskedSeed, seedMask) + # Step 3e + dbMask = self._mgf(seed, k-hLen-1) + # Step 3f + db = strxor(maskedDB, dbMask) + # Step 3g + valid = 1 + one = db[hLen:].find(bchr(0x01)) + lHash1 = db[:hLen] + if lHash1!=lHash: + valid = 0 + if one<0: + valid = 0 + if bord(y)!=0: + valid = 0 + if not valid: + raise ValueError("Incorrect decryption.") + # Step 4 + return db[hLen+one+1:] + +def new(key, hashAlgo=None, mgfunc=None, label=b('')): + """Return a cipher object `PKCS1OAEP_Cipher` that can be used to perform PKCS#1 OAEP 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. + hashAlgo : hash object + The hash function to use. This can be a module under `Crypto.Hash` + or an existing hash object created from any of such modules. If not specified, + `Crypto.Hash.SHA` (that is, SHA-1) is used. + mgfunc : callable + A mask generation function that accepts two parameters: a string to + use as seed, and the lenth of the mask to generate, in bytes. + If not specified, the standard MGF1 is used (a safe choice). + label : string + A label to apply to this particular encryption. If not specified, + an empty string is used. Specifying a label does not improve + security. + + :attention: Modify the mask generation function only if you know what you are doing. + Sender and receiver must use the same one. + """ + return PKCS1OAEP_Cipher(key, hashAlgo, mgfunc, label) + |