OAEP_DECODE: function()

in src/rsa.js [409:504]
77 lines of code
23 McCabe index (conditional complexity)

        OAEP_DECODE: function(sha, p, f) {
            var olen = RSA.RFS - 1,
                SEED = [],
                CHASH = [],
                DBMASK = [],
                comp,
                hlen,
                seedlen,
                x, t, d, i, k, h, r;

            seedlen = hlen = sha;

            if (olen < seedlen + hlen + 1) {
                return null;
            }

            for (i = 0; i < olen - seedlen; i++) {
                DBMASK[i] = 0;
            }

            if (f.length < RSA.RFS) {
                d = RSA.RFS - f.length;
                for (i = RSA.RFS - 1; i >= d; i--) {
                    f[i] = f[i - d];
                }
                for (i = d - 1; i >= 0; i--) {
                    f[i] = 0;
                }
            }

            h = this.hashit(sha, p, -1);
            for (i = 0; i < hlen; i++) {
                CHASH[i] = h[i];
            }

            x = f[0];

            for (i = seedlen; i < olen; i++) {
                DBMASK[i - seedlen] = f[i + 1];
            }

            this.MGF1(sha, DBMASK, seedlen, SEED);
            for (i = 0; i < seedlen; i++) {
                SEED[i] ^= f[i + 1];
            }
            this.MGF1(sha, SEED, olen - seedlen, f);
            for (i = 0; i < olen - seedlen; i++) {
                DBMASK[i] ^= f[i];
            }

            comp = true;
            for (i = 0; i < hlen; i++) {
                if (CHASH[i] != DBMASK[i]) {
                    comp = false;
                }
            }

            for (i = 0; i < olen - seedlen - hlen; i++) {
                DBMASK[i] = DBMASK[i + hlen];
            }

            for (i = 0; i < hlen; i++) {
                SEED[i] = CHASH[i] = 0;
            }

            for (k = 0;; k++) {
                if (k >= olen - seedlen - hlen) {
                    return null;
                }

                if (DBMASK[k] !== 0) {
                    break;
                }
            }

            t = DBMASK[k];

            if (!comp || x !== 0 || t != 0x01) {
                for (i = 0; i < olen - seedlen; i++) {
                    DBMASK[i] = 0;
                }
                return null;
            }

            r = [];

            for (i = 0; i < olen - seedlen - hlen - k - 1; i++) {
                r[i] = DBMASK[i + k + 1];
            }

            for (i = 0; i < olen - seedlen; i++) {
                DBMASK[i] = 0;
            }

            return r;
        },