TKIP中MIC值的算法及实现

2024-02-22 06:38

文章标签 算法实现 mic tkip

本文主要是介绍TKIP中MIC值的算法及实现，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

    针对WEP中CRC不能有效提供数据完整性保护的问题，TKIP 采用了带密钥的消息完整性校验算法MIC，目前TKIP的 MIC 算法称为 Michael。
    Michael 的认证密钥Kmic是 64 bits，分为左右各 32 bits 用(K0,K1)表示， Michael连接函数将消息M按32 bits分割成M0、M1、M2?Mn，最后生成64 bits的MIC值，接收方用共享的K和接收到的消息计算出MIC'与接收到的MIC进行校验，具体过程如下：

Algorithm 1:Michael message processing
    Input: Key (K0, K1) and message M0,?,MN
    Output: MIC value (V0, V1)
        MICHAEL((K0, K1) , (M0,?,MN))
            (L,R)←(K0, K1)
            for i=0 to N-1 do
                L←L ⊕ Mi
                (L, R)←b( L, R )
            return (L,R)
   Algorithm 2:Michael b function
    Input: (L,R)
    Output: (L,R)
        b(L,R)
        R←R⊕(L <<< 17)
        L←(L + R) mod 2^^32
        R←R⊕XSWAP(L)
        L←(L + R) mod 2^^32
        R←R⊕(L <<< 3)
        L←(L + R) mod 2^^32
        R←R⊕(L >>> 2)
        L←(L + R) mod 2^^32
        return (L,R)
> >>表示32 bits右旋转（rotation）， <<<表示32 bits左旋转。2^^32表示2的32次方。XSWAP 是一个交换函数， XSWAP （ABCD） =BADC，这里A、 B、 C、 D表示字节。
具体代码为：
unsigned long rol17(unsigned long w)             // rotate left 17
{
register unsigned long t, q;
    t = w << 17;
    q = (w >> 15);
    return(t|q);
}

unsigned long rol3(unsigned long w)             // rotate left 3
{
register unsigned long t, q;
    t = w << 3;
    q = (w >> 29);
    return(t|q);
}

unsigned long ror2(unsigned long w)             // rotate right 2
{
register unsigned long t, q;
    t = (w >> 2);
    q = w << 30;
    return(t|q);
}

#define    MBLOCK(L, R)                        /
    R = R ^ rol17(L);                    /
    L += R;                            /
    R ^= ((L & 0xff00ff00)>>8)|((L & 0x00ff00ff) << 8);    /
    L += R;                            /
    R ^= rol3(L);                        /
    L += R;                            /
    R ^= ror2(L);                        /
    L += R;

static unsigned long getw(unsigned char *cp)
{
register unsigned long t;

    t = 0;
    t = *cp++;
    t |= (*cp++)<<8;
    t |= (*cp++)<<16;
    t |= (*cp++)<<24;
    return(t);
}

void putw(unsigned long w, unsigned char *cp)
{

    *cp++ = (short int)w;    // MS compiler forces use of 0xff
    *cp++ = (short int)(w>>8);
    *cp++ = (short int)(w>>16);
    *cp++ = (short int)(w>>24);
    return;
}

// Michael integrity function
// pads the buffer (s) with up to 7 bytes
// if h is non-null, it is prepended to the buffer.
// The function appends an additional 8 bytes of Michael
// returns buffer len (payload+Michael)
//
int
Michael(unsigned char *key, unsigned char *s, int dlen)
{
register unsigned long M;
unsigned long L, R;
int len = dlen;
register unsigned char *sp, *cp;

    L = getw(key);        // L = *LL; R = *RR;
    R = getw(key+4);

    sp = s;
    sp[len++] = 0x5a;            // message padding
    sp[len++] = 0;                // 4 required
    sp[len++] = 0;
    sp[len++] = 0;
    sp[len++] = 0;
    while (len&0x3) {            // word aligned
        sp[len++] = 0;
    }

    sp = s;
    while (len > 0) {
        M = getw(sp);             // M = *mp++; len -= 4;
        sp+=4; len -= 4;

        L ^= M;                // Michael block function
        MBLOCK(L, R);
    }
    cp = s+dlen;
    putw(L, (unsigned char *)cp);
    cp = s+dlen+4;
    putw(R, (unsigned char *)cp);
    return(len+8);
}