Caesar cipher

• 网络安全凯撒密码作业，C写着没意思，所以想用汇编写。

C语言

/*
 * =====================================================================================
 *
 *       Filename:  Caesar_cipher.c
 *
 *    Description:  Caesar cipher
 *
 *        Version:  1.0
 *        Created:  2020年04月02日 12时02分48秒
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  Kali-Team (KT), root@kali-team.cn
 *   Organization:  
 *
 * =====================================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
 
#define caesar(x) rot(13, x)
#define decaesar(x) rot(13, x)
#define decrypt_rot(x, y) rot((26-x), y)
 
void rot(int c, char *str)
{
	int l = strlen(str);
	const char *alpha[2] = { "abcdefghijklmnopqrstuvwxyz", "ABCDEFGHIJKLMNOPQRSTUVWXYZ"};
	int i;
	for (i = 0; i < l; i++)
	{
        if (!isalpha(str[i]))
            continue;
        if (isupper(str[i]))
            str[i] = alpha[1][((int)(tolower(str[i]) - 'a') + c) % 26];
        else
            str[i] = alpha[0][((int)(tolower(str[i]) - 'a') + c) % 26];
    }
}
 
int main()
{
	char str[] = "This is a top secret text message!";
 
	printf("Original: %s
", str);
	caesar(str);
	printf("Encrypted: %s
", str);
	decaesar(str);
	printf("Decrypted: %s
", str);
 
	return 0;
}

C语言加内联汇编

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
 
#define caesar(x) rot(13, x, strlen(x))
#define decaesar(x) rot(13, x, strlen(x))
#define decrypt_rot(x, y) rot((26-x), y, strlen(y))

void rot(int c, char *str, int l)
{
	char alpha_down[27];
	   __asm
   {	
		mov byte ptr [ebp-17h],66h
		mov byte ptr [ebp-2],0
		mov byte ptr [ebp-15h],68h
		mov byte ptr [ebp-0Ch],71h
		mov byte ptr [ebp-19h],64h
		mov byte ptr [ebp-1Bh],62h
		mov byte ptr [ebp-4],79h
		mov byte ptr [ebp-14h],69h
		mov byte ptr [ebp-8],75h
		mov byte ptr [ebp-13h],6Ah
		mov byte ptr [ebp-5],78h
		mov byte ptr [ebp-12h],6Bh
		mov byte ptr [ebp-16h],67h
		mov byte ptr [ebp-1Ah],63h
		mov byte ptr [ebp-1Ch],61h
		mov byte ptr [ebp-11h],6Ch
		mov byte ptr [ebp-3],7Ah
		mov byte ptr [ebp-10h],6Dh
		mov byte ptr [ebp-0Fh],6Eh
		mov byte ptr [ebp-18h],65h
		mov byte ptr [ebp-0Eh],6Fh
		mov byte ptr [ebp-0Dh],70h
		mov byte ptr [ebp-6],77h
		mov byte ptr [ebp-0Ah],73h
		mov byte ptr [ebp-7],76h
		mov byte ptr [ebp-0Bh],72h
		mov byte ptr [ebp-9],74h
   }
	char alpha_up[27];
	__asm{
		mov byte ptr [ebp-1Eh],0
		mov byte ptr [ebp-35h],44h
		mov byte ptr [ebp-38h],41h
		mov byte ptr [ebp-34h],45h
		mov byte ptr [ebp-22h],57h
		mov byte ptr [ebp-36h],43h
		mov byte ptr [ebp-24h],55h
		mov byte ptr [ebp-2Ah],4Fh
		mov byte ptr [ebp-30h],49h
		mov byte ptr [ebp-21h],58h
		mov byte ptr [ebp-37h],42h
		mov byte ptr [ebp-2Fh],4Ah
		mov byte ptr [ebp-2Eh],4Bh
		mov byte ptr [ebp-2Dh],4Ch
		mov byte ptr [ebp-33h],46h
		mov byte ptr [ebp-20h],59h
		mov byte ptr [ebp-2Ch],4Dh
		mov byte ptr [ebp-32h],47h
		mov byte ptr [ebp-2Bh],4Eh
		mov byte ptr [ebp-29h],50h
		mov byte ptr [ebp-28h],51h
		mov byte ptr [ebp-27h],52h
		mov byte ptr [ebp-25h],54h
		mov byte ptr [ebp-1Fh],5Ah
		mov byte ptr [ebp-26h],53h
		mov byte ptr [ebp-31h],48h
		mov byte ptr [ebp-23h],56h
	}
	char *alpha[2];
	__asm{
		lea         eax,alpha_down
		mov         dword ptr [ebp-40h],eax
		lea         ecx,alpha_up
		mov         dword ptr [ebp-3Ch],ecx
	}

	for (int i = 0; i < l; i++)
	{
		if (!isalpha(str[i]))
			__asm jmp         rot+111h
		if (isupper(str[i]))
		{
			int index,list = 0;
			__asm{
				mov         eax,dword ptr [ebp+0Ch]
				add         eax,dword ptr [ebp-44h]
				movsx       ecx,byte ptr [eax]
				push        ecx
				call        tolower
				add         esp,4
				mov         edx,dword ptr [ebp+8]
				lea         eax,[eax+edx-61h]
				mov         dword ptr [list],eax
			}
			//index = list % 26;
			__asm{
				xor			edx,edx
				mov         ecx,1Ah
				div         ecx
				mov			dword ptr [index],edx

			}
			//str[i] = alpha[1][index];
			__asm{
				mov         eax,dword ptr [ebp+0Ch]
				add         eax,dword ptr [ebp-44h]
				mov         ecx,dword ptr [ebp-3Ch]
				add         ecx,dword ptr [index]
				mov         dl,byte ptr [ecx]
				mov         byte ptr [eax],dl
				}
			
		}
		else
		{

			int index,list = 0;

			//list = (int)(tolower(str[i]) - 97) + c;
			__asm{
				mov         eax,dword ptr [ebp+0Ch]
				add         eax,dword ptr [ebp-44h]
				movsx       ecx,byte ptr [eax]
				push        ecx
				call        tolower
				add         esp,4
				mov         edx,dword ptr [ebp+8]
				lea         eax,[eax+edx-61h]
				mov         dword ptr [list],eax

			}
			//index = list % 26;
			__asm{
				xor			edx,edx
				mov         ecx,1Ah
				div         ecx
				mov			dword ptr [index],edx
			}
			//str[i] = alpha[0][index];
			__asm{
				mov         eax,dword ptr [ebp+0Ch]
				add         eax,dword ptr [ebp-44h]
				mov         ecx,dword ptr [ebp-40h]
				add         ecx,dword ptr [index]
				mov         dl,byte ptr [ecx]
				mov         byte ptr [eax],dl

			}
		}
	}
	
}
 
 
int main()
{
	char str[] = "This is a top secret text message!";
	printf("Original: %s
", str);
	caesar(str);
	printf("Encrypted: %s
", str);
	decaesar(str);
	printf("Decrypted: %s
", str);
 
	return 0;
}