如何对两个C字符数组按位进行XOR?

问题描述

我对无法解决这个问题感到很傻，但是我迷路了.我正在尝试对两个C字符串进行XOR.

I feel silly for not being able to figure this out, but I am lost. I am trying to XOR two C strings.

#include <stdio.h>
#include <memory.h>
#include <stdlib.h>
int main()
{
    char plainone[16];
    char plaintwo[16];
    char xor[17];
    strcpy(plainone, "PlainOne");
    strcpy(plaintwo, "PlainTwo");
    int i=0;
    for(i=0; i<strlen(plainone);i++)
        xor[i] ^= (char)(plainone[i] ^ plaintwo[i]);
    printf("PlainText One: %s\nPlainText Two: %s\n\none^two: %s\n", plainone, plaintwo, xor);
    return 0;
}

我的输出是:

$ ./a.out
PlainText One: PlainOne
PlainText Two: PlainTwo

one^two:

为什么xor数组不读取任何内容?

Why doesn't the xor array read as anything?

推荐答案

一旦处理了XOR，就将处理可能不是可打印ASCII字符的二进制字节.

Once you are dealing with XOR, you are dealing with binary bytes that might not be printable ASCII characters.

当您对相同的字符进行XOR运算时，您将获得0.因此'P' ^ 'P'将为0.这是一个NUL字节，它终止了字符串.如果尝试使用printf()进行打印，则不会获得任何帮助； printf()认为该字符串是终止的长度为0的字符串.

And when you XOR the same characters with each other, you get a 0. So 'P' ^ 'P' will be 0. That's a NUL byte and it terminates the string. If you try to print with printf() you get nothing; printf() considers the string to be a terminated length-0 string.

此外，您应该仅使用=将XOR结果分配到目标缓冲区中，而不要像程序那样使用^=.

Also, you should simply assign the XOR result into your target buffer with = rather than using ^= as your program did.

这是我的程序版本，以及我的输出:

Here's my version of your program, and my output:

#include <stdio.h>
#include <memory.h>
#include <stdlib.h>

#define LENGTH 16
int main()
{
    char const plainone[LENGTH] = "PlainOne";
    char const plaintwo[LENGTH] = "PlainTwo";
    char xor[LENGTH];
    int i;

    for(i=0; i<LENGTH; ++i)
        xor[i] = (char)(plainone[i] ^ plaintwo[i]);
    printf("PlainText One: %s\nPlainText Two: %s\n\none^two: ", plainone, plaintwo);
    for(i=0; i<LENGTH; ++i)
        printf("%02X ", xor[i]);
    printf("\n");
    return 0;
}

输出:

PlainText One: PlainOne
PlainText Two: PlainTwo

one^two: 00 00 00 00 00 1B 19 0A 00 00 00 00 00 00 00 00

请注意前五个字节是如何全部为00，因为Plain与Plain进行了异或.

Notice how the first five bytes are all 00 because Plain is XORed with Plain.

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