rc4.c

这是一个对U盘读写等操作控制的过滤驱动程序

#include "rc4.h"

void rc4_setup( struct rc4_state *s, unsigned char *key,  int length )
{
    int i, j, k, *m, a;

    s->x = 0;
    s->y = 0;
    m = s->m;

    for( i = 0; i < 256; i++ )
    {
        m[i] = i;
    }

    j = k = 0;

    for( i = 0; i < 256; i++ )
    {
        a = m[i];
        j = (unsigned char) ( j + a + key[k] );
        m[i] = m[j]; m[j] = a;
        if( ++k >= length ) k = 0;
    }
}

void rc4_crypt( struct rc4_state *s, unsigned char *data, int length )
{ 
    int i, x, y, *m, a, b;

    x = s->x;
    y = s->y;
    m = s->m;

    for( i = 0; i < length; i++ )
    {
        x = (unsigned char) ( x + 1 ); a = m[x];
        y = (unsigned char) ( y + a );
        m[x] = b = m[y];
        m[y] = a;
        data[i] ^= m[(unsigned char) ( a + b )];
    }

    s->x = x;
    s->y = y;
}

VOID
EncryptBuf_128RC4(
				  IN OUT PBYTE Buf,
				  IN ULONG Length
				  )
{
	ULONG Offset = 0;
	ULONG i=0;
	struct rc4_state *s = NULL;
	UCHAR keys[8]={0x01,0x23,0x45,0x67,0x89,0xab,0xcd,0xef};
	UCHAR buffer[1024];	

	s =ExAllocatePool(NonPagedPool, sizeof(struct rc4_state));
	//注意：以1024为基本单位加密
	
	for (Offset=0; Offset<Length; Offset+=1024)
	{
		rc4_setup(s, keys, 8);
        memcpy(buffer, Buf+Offset, 1024);
		rc4_crypt(s, buffer, 1024);
        memcpy(Buf+Offset, buffer, 1024);
    }

	ExFreePool(s);
	
	//for (i=0; i<Length; i++) Buf[i] ^= 0xff;
}