roboot/boot/xtea.c

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/* ================================================================================ *//* ================================================================================= */

#include "xtea.h"


#define STORE32L(x, y)                      \
    do {                                    \
        (y)[3] = (uint8_t)(((x)>>24)&255);  \
        (y)[2] = (uint8_t)(((x)>>16)&255);  \
        (y)[1] = (uint8_t)(((x)>>8)&255);   \
        (y)[0] = (uint8_t)((x)&255);        \
    } while (0)

#define LOAD32L(x, y)                           \
    do {                                        \
        (x) = ((uint32_t)((y)[3] & 255)<<24) |  \
              ((uint32_t)((y)[2] & 255)<<16) |  \
              ((uint32_t)((y)[1] & 255)<<8)  |  \
              ((uint32_t)((y)[0] & 255));       \
    } while (0)



static void xtea_encrypt(const uint8_t *pt, uint8_t *ct, XteaStateKey_T *skey);


/**************************************************************************************************\
\**************************************************************************************************/
void XteaSetup(const uint8_t *key, const uint8_t *iv, XteaStateKey_T *skey)
{
    uint32_t x;
    uint32_t sum;
    uint32_t K[4];

    //assert(key != NULL);
    //assert(skey != NULL);

    for(x = 0; x < XTEA_BLOCKLEN; x++)
    {
        if (iv)
        {
            skey->IV[x] = iv[x];
        }
        else
        {
            skey->IV[x] = x;
        }
    }

    /* load key */
    LOAD32L(K[0], key+0);
    LOAD32L(K[1], key+4);
    LOAD32L(K[2], key+8);
    LOAD32L(K[3], key+12);

    sum = 0;
    for (x = 0; x < 32; x++)
    {
        skey->A[x] = sum + K[sum & 3U];
        sum = sum + 0x9E3779B9UL;
        skey->B[x] = sum + K[(sum>>11) & 3U];
    }

    XteaRestart(skey);
}


/**************************************************************************************************\
\**************************************************************************************************/
void XteaRestart(XteaStateKey_T *skey)
{
    uint32_t x;

    //assert(skey != NULL);

    for(x = 0; x < XTEA_BLOCKLEN; x++)
    {
        skey->pad[x] = skey->IV[x];
    }

    skey->padlen = XTEA_BLOCKLEN;
}


/**************************************************************************************************\
\**************************************************************************************************/
void XteaEncrypt(const uint8_t *pt, uint8_t *ct, uint32_t len, XteaStateKey_T *skey)
{
    while (len)
    {
        //assert(pt != NULL);
        //assert(ct != NULL);
        //assert(skey != NULL);

        if (XTEA_BLOCKLEN == skey->padlen)
        {
            xtea_encrypt(skey->pad, skey->pad, skey);
            skey->padlen = 0;
        }
        *ct++ = *pt++ ^ skey->pad[skey->padlen++];
        len--;
    }
}

/**************************************************************************************************\
\**************************************************************************************************/
void XteaDecrypt(const uint8_t *ct, uint8_t *pt, uint32_t len, XteaStateKey_T *skey)
{
    XteaEncrypt(ct, pt, len, skey);
}


/**************************************************************************************************\
\**************************************************************************************************/
static void xtea_encrypt(const uint8_t *pt, uint8_t *ct, XteaStateKey_T *skey)
{
    uint32_t y;
    uint32_t z;
    uint32_t r;

    LOAD32L(y, &pt[0]);
    LOAD32L(z, &pt[4]);

    for (r = 0; r < 32; r += 4)
    {
        y = y + ((((z<<4)^(z>>5)) + z) ^ skey->A[r]);
        z = z + ((((y<<4)^(y>>5)) + y) ^ skey->B[r]);

        y = y + ((((z<<4)^(z>>5)) + z) ^ skey->A[r+1]);
        z = z + ((((y<<4)^(y>>5)) + y) ^ skey->B[r+1]);

        y = y + ((((z<<4)^(z>>5)) + z) ^ skey->A[r+2]);
        z = z + ((((y<<4)^(y>>5)) + y) ^ skey->B[r+2]);

        y = y + ((((z<<4)^(z>>5)) + z) ^ skey->A[r+3]);
        z = z + ((((y<<4)^(y>>5)) + y) ^ skey->B[r+3]);
    }

    STORE32L(y, &ct[0]);
    STORE32L(z, &ct[4]);
}

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