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+# -*- coding: utf-8 -*-
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+#
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+# Cipher/PKCS1_OAEP.py : PKCS#1 OAEP
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+#
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+# ===================================================================
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+# The contents of this file are dedicated to the public domain. To
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+# the extent that dedication to the public domain is not available,
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+# everyone is granted a worldwide, perpetual, royalty-free,
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+# non-exclusive license to exercise all rights associated with the
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+# contents of this file for any purpose whatsoever.
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+# No rights are reserved.
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+#
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+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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+# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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+# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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+# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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+# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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+# SOFTWARE.
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+# ===================================================================
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+
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+from Crypto.Signature.pss import MGF1
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+import Crypto.Hash.SHA1
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+
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+from Crypto.Util.py3compat import bord, _copy_bytes
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+import Crypto.Util.number
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+from Crypto.Util.number import ceil_div, bytes_to_long, long_to_bytes
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+from Crypto.Util.strxor import strxor
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+from Crypto import Random
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+from hashlib import sha1
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+import gmpy2
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+
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+class PKCS1OAEP_Cipher:
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+ """Cipher object for PKCS#1 v1.5 OAEP.
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+ Do not create directly: use :func:`new` instead."""
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+
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+ def __init__(self, key, hashAlgo, mgfunc, label, randfunc):
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+ """Initialize this PKCS#1 OAEP cipher object.
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+
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+ :Parameters:
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+ key : an RSA key object
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+ If a private half is given, both encryption and decryption are possible.
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+ If a public half is given, only encryption is possible.
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+ hashAlgo : hash object
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+ The hash function to use. This can be a module under `Crypto.Hash`
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+ or an existing hash object created from any of such modules. If not specified,
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+ `Crypto.Hash.SHA1` is used.
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+ mgfunc : callable
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+ A mask generation function that accepts two parameters: a string to
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+ use as seed, and the lenth of the mask to generate, in bytes.
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+ If not specified, the standard MGF1 consistent with ``hashAlgo`` is used (a safe choice).
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+ label : bytes/bytearray/memoryview
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+ A label to apply to this particular encryption. If not specified,
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+ an empty string is used. Specifying a label does not improve
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+ security.
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+ randfunc : callable
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+ A function that returns random bytes.
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+
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+ :attention: Modify the mask generation function only if you know what you are doing.
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+ Sender and receiver must use the same one.
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+ """
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+ self._key = key
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+
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+ if hashAlgo:
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+ self._hashObj = hashAlgo
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+ else:
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+ self._hashObj = Crypto.Hash.SHA1
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+
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+ if mgfunc:
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+ self._mgf = mgfunc
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+ else:
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+ self._mgf = lambda x,y: MGF1(x,y,self._hashObj)
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+
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+ self._label = _copy_bytes(None, None, label)
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+ self._randfunc = randfunc
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+
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+ def can_encrypt(self):
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+ """Legacy function to check if you can call :meth:`encrypt`.
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+
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+ .. deprecated:: 3.0"""
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+ return self._key.can_encrypt()
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+
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+ def can_decrypt(self):
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+ """Legacy function to check if you can call :meth:`decrypt`.
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+
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+ .. deprecated:: 3.0"""
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+ return self._key.can_decrypt()
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+
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+ def encrypt(self, message):
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+ """Encrypt a message with PKCS#1 OAEP.
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+
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+ :param message:
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+ The message to encrypt, also known as plaintext. It can be of
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+ variable length, but not longer than the RSA modulus (in bytes)
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+ minus 2, minus twice the hash output size.
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+ For instance, if you use RSA 2048 and SHA-256, the longest message
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+ you can encrypt is 190 byte long.
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+ :type message: bytes/bytearray/memoryview
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+
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+ :returns: The ciphertext, as large as the RSA modulus.
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+ :rtype: bytes
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+
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+ :raises ValueError:
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+ if the message is too long.
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+ """
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+
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+ # See 7.1.1 in RFC3447
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+ modBits = Crypto.Util.number.size(self._key.n)
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+ k = ceil_div(modBits, 8) # Convert from bits to bytes
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+ hLen = self._hashObj.digest_size
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+ mLen = len(message)
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+
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+ # Step 1b
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+ ps_len = k - mLen - 2 * hLen - 2
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+ if ps_len < 0:
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+ raise ValueError("Plaintext is too long.")
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+ # Step 2a
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+ lHash = sha1(self._label).digest()
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+ # Step 2b
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+ ps = b'\x00' * ps_len
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+ # Step 2c
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+ db = lHash + ps + b'\x01' + _copy_bytes(None, None, message)
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+ # Step 2d
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+ ros = self._randfunc(hLen)
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+ # Step 2e
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+ dbMask = self._mgf(ros, k-hLen-1)
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+ # Step 2f
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+ maskedDB = strxor(db, dbMask)
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+ # Step 2g
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+ seedMask = self._mgf(maskedDB, hLen)
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+ # Step 2h
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+ maskedSeed = strxor(ros, seedMask)
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+ # Step 2i
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+ em = b'\x00' + maskedSeed + maskedDB
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+ # Step 3a (OS2IP)
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+ em_int = bytes_to_long(em)
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+ # Step 3b (RSAEP)
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+ m_int = gmpy2.powmod(em_int, self._key.e, self._key.n)
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+ # Step 3c (I2OSP)
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+ c = long_to_bytes(m_int, k)
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+ return c
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+
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+ def decrypt(self, ciphertext):
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+ """Decrypt a message with PKCS#1 OAEP.
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+
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+ :param ciphertext: The encrypted message.
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+ :type ciphertext: bytes/bytearray/memoryview
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+
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+ :returns: The original message (plaintext).
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+ :rtype: bytes
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+
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+ :raises ValueError:
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+ if the ciphertext has the wrong length, or if decryption
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+ fails the integrity check (in which case, the decryption
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+ key is probably wrong).
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+ :raises TypeError:
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+ if the RSA key has no private half (i.e. you are trying
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+ to decrypt using a public key).
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+ """
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+ # See 7.1.2 in RFC3447
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+ modBits = Crypto.Util.number.size(self._key.n)
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+ k = ceil_div(modBits,8) # Convert from bits to bytes
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+ hLen = self._hashObj.digest_size
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+ # Step 1b and 1c
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+ if len(ciphertext) != k or k<hLen+2:
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+ raise ValueError("Ciphertext with incorrect length.")
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+ # Step 2a (O2SIP)
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+ ct_int = bytes_to_long(ciphertext)
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+ # Step 2b (RSADP)
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+ # m_int = self._key._decrypt(ct_int)
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+ m_int = gmpy2.powmod(ct_int, self._key.d, self._key.n)
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+ # Complete step 2c (I2OSP)
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+ em = long_to_bytes(m_int, k)
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+ # Step 3a
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+ lHash = sha1(self._label).digest()
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+ # Step 3b
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+ y = em[0]
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+ # y must be 0, but we MUST NOT check it here in order not to
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+ # allow attacks like Manger's (http://dl.acm.org/citation.cfm?id=704143)
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+ maskedSeed = em[1:hLen+1]
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+ maskedDB = em[hLen+1:]
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+ # Step 3c
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+ seedMask = self._mgf(maskedDB, hLen)
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+ # Step 3d
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+ seed = strxor(maskedSeed, seedMask)
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+ # Step 3e
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+ dbMask = self._mgf(seed, k-hLen-1)
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+ # Step 3f
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+ db = strxor(maskedDB, dbMask)
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+ # Step 3g
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+ one_pos = hLen + db[hLen:].find(b'\x01')
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+ lHash1 = db[:hLen]
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+ invalid = bord(y) | int(one_pos < hLen)
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+ hash_compare = strxor(lHash1, lHash)
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+ for x in hash_compare:
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+ invalid |= bord(x)
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+ for x in db[hLen:one_pos]:
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+ invalid |= bord(x)
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+ if invalid != 0:
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+ raise ValueError("Incorrect decryption.")
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+ # Step 4
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+ return db[one_pos + 1:]
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+
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+def new(key, hashAlgo=None, mgfunc=None, label=b'', randfunc=None):
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+ """Return a cipher object :class:`PKCS1OAEP_Cipher` that can be used to perform PKCS#1 OAEP encryption or decryption.
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+
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+ :param key:
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+ The key object to use to encrypt or decrypt the message.
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+ Decryption is only possible with a private RSA key.
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+ :type key: RSA key object
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+
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+ :param hashAlgo:
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+ The hash function to use. This can be a module under `Crypto.Hash`
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+ or an existing hash object created from any of such modules.
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+ If not specified, `Crypto.Hash.SHA1` is used.
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+ :type hashAlgo: hash object
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+
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+ :param mgfunc:
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+ A mask generation function that accepts two parameters: a string to
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+ use as seed, and the lenth of the mask to generate, in bytes.
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+ If not specified, the standard MGF1 consistent with ``hashAlgo`` is used (a safe choice).
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+ :type mgfunc: callable
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+
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+ :param label:
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+ A label to apply to this particular encryption. If not specified,
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+ an empty string is used. Specifying a label does not improve
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+ security.
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+ :type label: bytes/bytearray/memoryview
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+
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+ :param randfunc:
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+ A function that returns random bytes.
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+ The default is `Random.get_random_bytes`.
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+ :type randfunc: callable
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+ """
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+
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+ if randfunc is None:
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+ randfunc = Random.get_random_bytes
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+ return PKCS1OAEP_Cipher(key, hashAlgo, mgfunc, label, randfunc)
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+
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+
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+def new(key, hashAlgo=None, mgfunc=None, label=b'', randfunc=None):
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+ """Return a cipher object :class:`PKCS1OAEP_Cipher` that can be used to perform PKCS#1 OAEP encryption or decryption.
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+
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+ :param key:
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+ The key object to use to encrypt or decrypt the message.
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+ Decryption is only possible with a private RSA key.
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+ :type key: RSA key object
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+
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+ :param hashAlgo:
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+ The hash function to use. This can be a module under `Crypto.Hash`
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+ or an existing hash object created from any of such modules.
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+ If not specified, `Crypto.Hash.SHA1` is used.
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+ :type hashAlgo: hash object
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+
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+ :param mgfunc:
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+ A mask generation function that accepts two parameters: a string to
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+ use as seed, and the lenth of the mask to generate, in bytes.
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+ If not specified, the standard MGF1 consistent with ``hashAlgo`` is used (a safe choice).
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+ :type mgfunc: callable
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+
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+ :param label:
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+ A label to apply to this particular encryption. If not specified,
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+ an empty string is used. Specifying a label does not improve
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+ security.
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+ :type label: bytes/bytearray/memoryview
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+
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+ :param randfunc:
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+ A function that returns random bytes.
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+ The default is `Random.get_random_bytes`.
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+ :type randfunc: callable
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+ """
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+
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+ if randfunc is None:
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+ randfunc = Random.get_random_bytes
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+ return PKCS1OAEP_Cipher(key, hashAlgo, mgfunc, label, randfunc)
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+
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