int OAEP_DECODE()

in src/rsa_support.c [215:276]

• 52 lines of code
• 11 McCabe index (conditional complexity)

int OAEP_DECODE(int sha,const octet *p,octet *f)
{
    int comp;
    int x;
    int t;
    int i;
    int k;
    int olen=f->max-1;
    int hlen;
    int seedlen;
    char dbmask[MAX_RSA_BYTES];
    char seed[64];
    char chash[64];
    octet DBMASK= {0,sizeof(dbmask),dbmask};
    octet SEED= {0,sizeof(seed),seed};
    octet CHASH= {0,sizeof(chash),chash};

    seedlen=hlen=sha;
    if (olen<seedlen+hlen+1) return 1;
    if (!OCT_pad(f,olen+1)) return 1;
    hashit(sha,p,-1,&CHASH);

    x=f->val[0];
    for (i=seedlen; i<olen; i++)
        DBMASK.val[i-seedlen]=f->val[i+1];
    DBMASK.len=olen-seedlen;

    MGF1(sha,&DBMASK,seedlen,&SEED);
    for (i=0; i<seedlen; i++) SEED.val[i]^=f->val[i+1];
    MGF1(sha,&SEED,olen-seedlen,f);
    OCT_xor(&DBMASK,f);

    comp=OCT_ncomp(&CHASH,&DBMASK,hlen);

    OCT_shl(&DBMASK,hlen);

    OCT_clear(&SEED);
    OCT_clear(&CHASH);

    for (k=0;; k++)
    {
        if (k>=DBMASK.len)
        {
            OCT_clear(&DBMASK);
            return 1;
        }
        if (DBMASK.val[k]!=0) break;
    }

    t=DBMASK.val[k];
    if (!comp || x!=0 || t!=0x01)
    {
        OCT_clear(&DBMASK);
        return 1;
    }

    OCT_shl(&DBMASK,k+1);
    OCT_copy(f,&DBMASK);
    OCT_clear(&DBMASK);

    return 0;
}