How to use the crypt.rng function in crypt

// 3. Generate an octet string PS consisting of emLen-||M||-2hLen-1 zero octets.
		var psLen = emLen - M.length - 2*hLen - 1;
		if (psLen < 0)
			throw new Error("malformed input");
		var PS = new Uint8Array(psLen + 1);
		PS.fill(0);
		PS[psLen] = 0x01;
		// 4. Let pHash = Hash(P)
		H.reset();
		H.update(P);
		var pHash = H.close();
		// 5. Concatenate pHash, PS, the message M, ...
		var DB = new ArrayBuffer();
		DB = DB.concat(pHash, PS, M);
		// 6. Generate a random octet string seed of length hLen.
		var seed = Crypt.rng(hLen);
		// 7. Let dbMask = MGF(seed, emLen - hLen).
		var dbMask = this.MGF(seed, emLen - hLen);
		// 8. Let maskedDB = DB \xor dbMask.
		this.xor(DB, dbMask);
		var maskedDB = DB;
		// 9. Let seedMask = MGF(maskedDB, hLen).
		var seedMask = this.MGF(maskedDB, hLen);
		// 10. Let maskedSeed = seed \xor seedMask.
		this.xor(seed, seedMask);
		var maskedSeed = seed;
		// 11. Let EM = maskedSeed || maskedDB.
		var EM = maskedSeed;
		EM = EM.concat(maskedDB);
		return new Arith.Integer(EM);
	};
	ncomp(a, b, l) {

emeEncode(M, emLen) {
		var pssize = emLen - M.byteLength - 2;
		if (pssize < 0)
			throw new Error("emeEncode malformed input");
		var s = new Uint8Array(pssize + 2);
		var ps = new Uint8Array(Crypt.rng(pssize));
		var i = 0;
		s[i++] = 0x02;
		for (var j = 0; j < ps.length; j++) {
			// make sure of nonzero
			var c = ps[j];
			if (c == 0)
				c = 0xff;
			s[i++] = c;
		}
		s[i++] = 0x00;
		return new Arith.Integer(s.buffer.concat(M));
	};
	emeDecode(EM) {

var mac = this.calculateMac(cipher.hmac, session.writeSeqNum, type, session.protocolVersion, fragment);
					var blksz = session.chosenCipher.cipherBlockSize, iv;
					var tmps = new SSLStream();
					tmps.writeChunk(fragment);
					tmps.writeChunk(mac);
					if (blksz) {
						var length = tmps.bytesWritten + 1;
						var padSize = length % blksz;
						if (padSize > 0)
							padSize = blksz - padSize;
						for (var i = 0; i < padSize; i++)
							tmps.writeChar(padSize);
						tmps.writeChar(padSize);
					}
					if (session.protocolVersion >= 0x302 && blksz) { // 3.2 or higher && block cipher
						iv = Crypt.rng(blksz);
						cipher.enc.setIV(iv);
					}
					fragment = cipher.enc.encrypt(tmps.getChunk());
					if (iv)
						fragment = iv.concat(fragment);
					break;
				case SSL.cipherSuite.GCM:
					let explicit_nonce = cipher.nonce.toChunk(session.chosenCipher.ivSize);
					cipher.nonce.inc();
					let nonce = cipher.iv.concat(explicit_nonce);
					let additional_data = this.aeadAdditionalData(session.writeSeqNum, type, session.protocolVersion, fragment.byteLength);
					fragment = cipher.enc.process(fragment, null, nonce, additional_data, true);
					fragment = explicit_nonce.concat(fragment);
					break;
				}
				session.writeSeqNum.inc();

static randint(max, z) {
		var i = new Arith.Integer(Crypt.rng(max.sizeof()));
		while (i.comp(max) >= 0)
			i = z.lsr(i, 1);
		return i;
	};
	static parse(buf, privFlag) {