c - 输入后程序转到空白终端(C 中的异或加密)

Question

这是一个带有一些支持函数的程序，用于进行简单的异或加密/解密。

可能有很多困惑的语法 - 尽管它当前编译没有错误 - 我的问题是它没有通过程序，所以我无法真正很好地测试它。

输入加密 key 后按 Enter 键后，终端屏幕变为空白，但程序不会退出。

如果有人想尝试查看它，或者运行它并亲自查看问题，我将保留下面的代码。这将非常有帮助 - 并且信息丰富，谢谢大家。

很抱歉，代码在某些地方缩进得不好 - 当我从编辑器复制和粘贴时，格式不太好，但我试图使其可读。

这是在 Ubuntu shell 的 VIM 编辑器中用 C 语言编写的。(v14.3)。

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

#define MAX_BUF  256

unsigned char getBit(unsigned char, int);
unsigned char setBit(unsigned char, int);
unsigned char clearBit(unsigned char, int);
unsigned char skipx(unsigned char, unsigned char);
unsigned char rotr(unsigned char);


int main()
{

    char str[8];
    unsigned  char c[MAX_BUF];
    unsigned  char key[MAX_BUF];

    int  choice;

    printf("\nYou may:\n");
    printf("  (1) Encrypt a message \n");
    printf("  (2) Decrypt a message \n");

    printf("\n  what is your selection: ");
    fgets(str, sizeof(str), stdin);
    sscanf(str, "%d", &choice);

    switch (choice)
    {
        case 1:
            printf("\nEnter plain text to be encrypted: ");
            fgets(c, sizeof(c),stdin);
            printf("Press enter to continue.");
            scanf("%c",c);

            //User interface: Ask user for encryption key
            printf("\nNow enter your encryption  key: ");
            fgets(key, sizeof(key),stdin);
            printf("Press enter to continue.");
            scanf("%c",key);

            int inputLen = strlen(c);

            int pos;

            for(pos = 0; pos < inputLen; pos++ )
            {
                skipx(c[pos], *key);
            }

            int pos2;

            for(pos2 = 0; pos2 < inputLen; pos++)
            {
                printf("%c", c[pos2]);
            }
            break;

        case 2://Decrypt message
            printf("\nEnter plain text to be decrypted: ");
            fgets(c, sizeof(c),stdin);
            printf("Press enter to continue.");
            scanf("%c",c);

            printf("\nNow enter your decryption  key: ");
            fgets(key, sizeof(key),stdin);
            printf("Press enter to continue.");
            scanf("%c",key);

            for(pos = 0; pos < inputLen; pos++ ){
            skipx(c[pos], *key);
            }

            //Prints the char array, after being XOR encrypted
            for(pos2 = 0; pos2 < inputLen; pos++){

            printf("%c", c[pos2]);

            }
            break;

        default:
            break;
    }

    return 0;
}

unsigned char skipx(unsigned char c, unsigned char key)
{
    int i; //for looping through the 8 positions of the bit

    for(i = 7; i > -1; i--) //Loops through byte, this will be the bit index
    {
        if(getBit(c,i) % 2 != 0) //only if the number isn't even. ->
        {
            setBit(getBit(c,i)^getBit(key,i-1),i);

            rotr(key);//rotate right to update key
        }
    }
}

unsigned char rotr(unsigned char c)
{
  unsigned char c1 = getBit(c,0) << 7;
  unsigned char c2 = c >> 1;

  return c1^c2;
}


unsigned char getBit(unsigned char c, int n)
{
  return (c & (1 << n)) >> n;
}


unsigned char setBit(unsigned char c, int n)
{
  return c | (1 << n);
}


unsigned char clearBit(unsigned char c, int n)
{
  return c & (~(1 << n));
}

Answer 1

您的问题是由拼写错误引起的

for(pos2 = 0; pos2 < inputLen; pos++)

您递增了错误的变量。应该是

for(pos2 = 0; pos2 < inputLen; pos2++)

我建议你启用-Wall编译你的代码，你会发现一些有趣的东西，比如:

test.c: In function ‘main’:
test.c:125:4: warning: ‘inputLen’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    for(pos = 0; pos < inputLen; pos++ ){
    ^

但是您的代码有很多错误:它无法执行预期的操作。