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Filename : strxor.py
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# ===================================================================
#
# Copyright (c) 2014, Legrandin <helderijs@gmail.com>
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
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#
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
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#    the documentation and/or other materials provided with the
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# ===================================================================

from Crypto.Util._raw_api import (load_pycryptodome_raw_lib, c_size_t,
                                  create_string_buffer, get_raw_buffer,
                                  c_uint8_ptr, is_writeable_buffer)

_raw_strxor = load_pycryptodome_raw_lib("Crypto.Util._strxor",
                    """
                    void strxor(const uint8_t *in1,
                                const uint8_t *in2,
                                uint8_t *out, size_t len);
                    void strxor_c(const uint8_t *in,
                                  uint8_t c,
                                  uint8_t *out,
                                  size_t len);
                    """)


def strxor(term1, term2, output=None):
    """XOR two byte strings.
    
    Args:
      term1 (bytes/bytearray/memoryview):
        The first term of the XOR operation.
      term2 (bytes/bytearray/memoryview):
        The second term of the XOR operation.
      output (bytearray/memoryview):
        The location where the result must be written to.
        If ``None``, the result is returned.
    :Return:
        If ``output`` is ``None``, a new ``bytes`` string with the result.
        Otherwise ``None``.
    """

    if len(term1) != len(term2):
        raise ValueError("Only byte strings of equal length can be xored")
    
    if output is None:
        result = create_string_buffer(len(term1))
    else:
        # Note: output may overlap with either input
        result = output
        
        if not is_writeable_buffer(output):
            raise TypeError("output must be a bytearray or a writeable memoryview")
        
        if len(term1) != len(output):
            raise ValueError("output must have the same length as the input"
                             "  (%d bytes)" % len(term1))

    _raw_strxor.strxor(c_uint8_ptr(term1),
                       c_uint8_ptr(term2),
                       c_uint8_ptr(result),
                       c_size_t(len(term1)))

    if output is None:
        return get_raw_buffer(result)
    else:
        return None


def strxor_c(term, c, output=None):
    """XOR a byte string with a repeated sequence of characters.

    Args:
        term(bytes/bytearray/memoryview):
            The first term of the XOR operation.
        c (bytes):
            The byte that makes up the second term of the XOR operation.
        output (None or bytearray/memoryview):
            If not ``None``, the location where the result is stored into.

    Return:
        If ``output`` is ``None``, a new ``bytes`` string with the result.
        Otherwise ``None``.
    """

    if not 0 <= c < 256:
        raise ValueError("c must be in range(256)")
    
    if output is None:
        result = create_string_buffer(len(term))
    else:
        # Note: output may overlap with either input
        result = output
       
        if not is_writeable_buffer(output):
            raise TypeError("output must be a bytearray or a writeable memoryview")
        
        if len(term) != len(output):
            raise ValueError("output must have the same length as the input"
                             "  (%d bytes)" % len(term))

    _raw_strxor.strxor_c(c_uint8_ptr(term),
                         c,
                         c_uint8_ptr(result),
                         c_size_t(len(term))
                         )

    if output is None:
        return get_raw_buffer(result)
    else:
        return None


def _strxor_direct(term1, term2, result):
    """Very fast XOR - check conditions!"""
    _raw_strxor.strxor(term1, term2, result, c_size_t(len(term1)))