int AES_CBC_IV0_DECRYPT()

in src/ecdh_support.c [293:344]

• 46 lines of code
• 18 McCabe index (conditional complexity)

int AES_CBC_IV0_DECRYPT(octet *k,const octet *c,octet *m)
{
    /* padding is removed */
    amcl_aes a;
    int i;
    int ipt;
    int opt;
    int ch;
    char buff[16];
    int fin;
    int bad;
    int padlen;
    ipt=opt=0;

    OCT_clear(m);
    if (c->len==0) return 1;
    ch=c->val[ipt++];

    AES_init(&a,CBC,k->len,k->val,NULL);
    fin=0;

    for(;;)
    {
        for (i=0; i<16; i++)
        {
            buff[i]=(char)ch;
            if (ipt>=c->len)
            {
                fin=1;
                break;
            }
            else ch=c->val[ipt++];
        }
        AES_decrypt(&a,buff);
        if (fin) break;
        for (i=0; i<16; i++)
            if (opt<m->max) m->val[opt++]=buff[i];
    }
    AES_end(&a);
    bad=0;
    padlen=buff[15];
    if (i!=15 || padlen<1 || padlen>16) bad=1;
    if (padlen>=2 && padlen<=16)
        for (i=16-padlen; i<16; i++) if (buff[i]!=padlen) bad=1;

    if (!bad) for (i=0; i<16-padlen; i++)
            if (opt<m->max) m->val[opt++]=buff[i];

    m->len=opt;
    if (bad) return 0;
    return 1;
}