pycryptodome/lib/Crypto/Util/strxor.py

# ===================================================================
#
# Copyright (c) 2014, Legrandin <helderijs@gmail.com>
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# ===================================================================

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

_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):
    """XOR of two byte strings.
    They must have equal length.

    Return:
        A new byte string, :data:`term1` xored with :data:`term2`.
    """

    expect_byte_string(term1)
    expect_byte_string(term2)
    if len(term1) != len(term2):
        raise ValueError("Only byte strings of equal length can be xored")
    result = create_string_buffer(len(term1))
    _raw_strxor.strxor(term1, term2, result, c_size_t(len(term1)))
    return get_raw_buffer(result)


def strxor_c(term, c):
    """XOR of a byte string with a repeated sequence of characters.

    Return:
        A new byte string, :data:`term` with all its bytes xored with :data:`c`.
    """

    expect_byte_string(term)
    if not 0 <= c < 256:
        raise ValueError("c must be in range(256)")
    result = create_string_buffer(len(term))
    _raw_strxor.strxor_c(term, c, result, c_size_t(len(term)))
    return get_raw_buffer(result)

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