int HMAC()

in src/ecdh_support.c [152:187]

• 23 lines of code
• 4 McCabe index (conditional complexity)

int HMAC(int sha,const octet *m,const octet *k,int olen,octet *tag)
{
    /* Input is from an octet m        *
     * olen is requested output length in bytes. k is the key  *
     * The output is the calculated tag */
    int hlen;
    int b;
    char h[128];
    char k0[128];
    octet H= {0,sizeof(h),h};
    octet K0= {0,sizeof(k0),k0};

    hlen=sha;
    if (hlen>32) b=128;
    else b=64;

    if (olen<4 /*|| olen>hlen*/) return 0;

    if (k->len > b) ehashit(sha,k,-1,NULL,&K0,0);
    else            OCT_copy(&K0,k);

    OCT_jbyte(&K0,0,b-K0.len);

    OCT_xorbyte(&K0,0x36);

    ehashit(sha,&K0,-1,m,&H,0);

    OCT_xorbyte(&K0,0x6a);   /* 0x6a = 0x36 ^ 0x5c */
    ehashit(sha,&K0,-1,&H,&H,olen);

    OCT_empty(tag);

    OCT_jbytes(tag,H.val,olen);

    return 1;
}