void GCM_init()

in src/gcm.c [157:192]

• 33 lines of code
• 6 McCabe index (conditional complexity)

void GCM_init(gcm* g,int nk,char *key,int niv,const char *iv)
{
    /* iv size niv is usually 12 bytes (96 bits). AES key size nk can be 16,24 or 32 bytes */
    uchar H[16];
    for (int i=0; i<16; i++)
    {
        H[i]=0;
        g->stateX[i]=0;
    }

    AES_init(&(g->a),ECB,nk,key,iv);
    AES_ecb_encrypt(&(g->a),H);     /* E(K,0) */
    precompute(g,H);

    g->lenA[0]=g->lenC[0]=g->lenA[1]=g->lenC[1]=0;
    if (niv==12)
    {
        for (int i=0; i<12; i++) g->a.f[i]=iv[i];
        unpack((unsign32)1,(uchar *)&(g->a.f[12]));  /* initialise IV */
        for (int i=0; i<16; i++) g->Y_0[i]=g->a.f[i];
    }
    else
    {
        g->status=GCM_ACCEPTING_CIPHER;
        GCM_ghash(g,iv,niv); /* GHASH(H,0,IV) */
        GCM_wrap(g);
        for (int i=0; i<16; i++)
        {
            g->a.f[i]=g->stateX[i];
            g->Y_0[i]=g->a.f[i];
            g->stateX[i]=0;
        }
        g->lenA[0]=g->lenC[0]=g->lenA[1]=g->lenC[1]=0;
    }
    g->status=GCM_ACCEPTING_HEADER;
}