peermessage-mod-kac

ies_test.java

	public void sendMessageToBob() throws Exception {
		Charset UTF8 = Charset.forName("UTF-8");
		String MAC_ALGO = "HmacSHA1";
		Mac MAC = Mac.getInstance(MAC_ALGO);
		MessageDigest SHA512 = MessageDigest.getInstance("SHA-512");
		Cipher AES = Cipher.getInstance("AES/CBC/PKCS5Padding");

		byte[] prefix = "pmsg-mod-kac".getBytes();

		NetworkParameters params = PPCNetParams.get();
		ECKey alice = new DumpedPrivateKey(params,
				"U5AJjxbyWtWpUtcfqUHj2tAgUXhd35eaX6qGz6wW1cE9RgRRLCSy").getKey();
		ECKey bob = new DumpedPrivateKey(params,
				"U8xAm8bnf7wvLVdNDm3sXZ1msb8JNJyAfTMNNrehfHrf47HaSobu").getKey();

		List<Entry<byte[], byte[]>> messages = new ArrayList<Map.Entry<byte[], byte[]>>();
		messages.add(new AbstractMap.SimpleEntry("Hi Bob, how are you? Let's meet".getBytes(UTF8),
				bob.getPubKey()));

		BigInteger feePerKB = BigInteger.valueOf(10 * 1000);
		BigInteger minOutputValue = BigInteger.valueOf(10 * 1000);

		// load input transaction
		byte[] prevRawTx = Hex
				.decodeHex("0100000039f6b85401ffe493177fc3771964b2b661982a69acee6392aa51a81b30535d12cbcc77e442010000006c493046022100fb276784fe6184daca38be1ec32561f0277c51d5c3843f04f6e005194a1ca9b5022100e84baafc6b195281f6077ed207b25f688277184214d2ae1d0fe04e00911e00b10121039bb033187a0d664e53e351f585f9d90d7dd1088b34e1ac3a970d55c5f45c77edffffffff0200a60e00000000001976a914db3b97012dc875a408d7bab2ea61f20295b6ac7a88ac30750000000000001976a9149421bf3690377d9004b2f2e9d2e1951589f55c9d88ac00000000"
						.toCharArray());
		Transaction prevTx = new Transaction(params, prevRawTx);
		TransactionOutPoint prevOutPoint = new TransactionOutPoint(params, 1, prevTx.getHash());
		TransactionOutput prevOut = prevTx.getOutput((int) prevOutPoint.getIndex());

		Transaction tx = new Transaction(params);
		tx.setTime(prevTx.getTime());
		tx.addInput(prevOut);

		for (Entry<byte[], byte[]> e : messages) {
			// http://en.wikipedia.org/wiki/Integrated_Encryption_Scheme
			byte[] m = e.getKey();
			if (m.length > 31) {
				throw new RuntimeException("message too long");
			}
			// generate initialization vector for AES/CBC from current output
			// index and prev tx hash
			SHA512.reset();
			SHA512.update(new VarInt(tx.getOutputs().size()).encode());
			SHA512.update(prevOutPoint.getHash().getBytes());
			byte[] IV = Arrays.copyOf(SHA512.digest(), 16);
			// generates a random number
			BigInteger r = alice.getPrivKey();
			// derives a shared secret
			ECPoint K_B = ECKey.fromPublicOnly(e.getValue()).getPubKeyPoint();
			BigInteger S = K_B.multiply(r).normalize().getAffineXCoord().toBigInteger();
			// uses KDF to derive a symmetric encryption and a MAC keys
			SHA512.reset();
			byte[] k_tmp = SHA512.digest(S.toByteArray());
			byte[] k_E = Arrays.copyOfRange(k_tmp, 0, 32);
			byte[] k_M = Arrays.copyOfRange(k_tmp, 32, 64);

			// encrypt the message
			AES.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(k_E, "AES"), new IvParameterSpec(IV));
			byte[] c = AES.doFinal(m);
			// computes the tag of encrypted message
			MAC.init(new SecretKeySpec(k_M, MAC_ALGO));
			byte[] d = MAC.doFinal(c);

			// create ScriptPubkey
			// from fake uncompressed public key
			byte[] pubKey = new byte[65];
			pubKey[0] = 0x04;
			System.arraycopy(prefix, 0, pubKey, 1, prefix.length);
			System.arraycopy(c, 0, pubKey, 1 + prefix.length, c.length);
			System.arraycopy(d, 0, pubKey, 1 + prefix.length + c.length, d.length);
			tx.addOutput(new TransactionOutput(params, tx, minOutputValue, ECKey
					.fromPublicOnly(pubKey)));
		}
		{ // sign input, adjust fee if needed
			BigInteger available = prevOut.getValue();
			BigInteger paid = minOutputValue.multiply(BigInteger.valueOf(tx.getOutputs().size()));

			BigInteger fee, feeReq = feePerKB, change;
			TransactionOutput changeTx = null;
			boolean changeOff = false;
			do {
				fee = feeReq;
				change = available.subtract(fee).subtract(paid);
				if (change.compareTo(BigInteger.ZERO) < 0) {
					throw new RuntimeException("insufficient funds");
				} else if (changeOff) {

				} else if (change.compareTo(minOutputValue) >= 0) {
					if (changeTx == null) {
						changeTx = tx.addOutput(change, alice.toAddress(params));
					} else {
						changeTx.setValue(change);
					}
				} else if (changeTx != null) {
					List<TransactionOutput> outs = tx.getOutputs();
					tx.clearOutputs();
					for (int i = 0; i < outs.size() - 1; i++) {
						tx.addOutput(outs.get(i));
					}
					changeTx = null;
					changeOff = true;
				}

				TransactionSignature sig = tx.calculateSignature(0, alice,
						prevOut.getScriptPubKey(), SigHash.ALL, false);
				tx.getInput(0).setScriptSig(ScriptBuilder.createInputScript(sig, alice));
				feeReq = BigInteger.valueOf(tx.bitcoinSerialize().length / 1000 + 1).multiply(
						feePerKB);
			} while (feeReq.compareTo(fee) > 0);
		}

		// broadcast tx

		// now Bob
		ECKey R = ECKey.fromPublicOnly(tx.getInput(0).getScriptSig().getPubKey());
		// derives the shared secret
		BigInteger S = R.getPubKeyPoint().multiply(bob.getPrivKey()).normalize().getAffineXCoord()
				.toBigInteger();
		outputs: for (int o = 0; o < tx.getOutputs().size(); o++) {
			TransactionOutput to = tx.getOutput(o);
			if (to.getScriptPubKey().isSentToRawPubKey()) {
				byte[] pubKey = to.getScriptPubKey().getPubKey();
				if (pubKey.length != 65) { // compressed
					continue;
				}
				for (int i = 0; i < prefix.length; i++) {
					if (pubKey[i + 1] != prefix[i]) {
						continue outputs;
					}
				}
				byte[] c = new byte[32];
				System.arraycopy(pubKey, 1 + prefix.length, c, 0, c.length);
				byte[] d = new byte[20];
				System.arraycopy(pubKey, 1 + prefix.length + c.length, d, 0, d.length);
				// derives keys the same way as Alice did
				byte[] k_tmp = SHA512.digest(S.toByteArray());
				byte[] k_E = Arrays.copyOfRange(k_tmp, 0, 32);
				byte[] k_M = Arrays.copyOfRange(k_tmp, 32, 64);
				// uses MAC to check the tag
				MAC.init(new SecretKeySpec(k_M, MAC_ALGO));
				byte[] d2 = MAC.doFinal(c);
				if (!Arrays.equals(d, d2)) {
					continue outputs;
				}
				// uses symmetric encryption scheme to decrypt the message
				SHA512.reset();
				SHA512.update(new VarInt(o).encode());
				SHA512.update(prevOutPoint.getHash().getBytes());
				byte[] IV = Arrays.copyOf(SHA512.digest(), 16);
				AES.init(Cipher.DECRYPT_MODE, new SecretKeySpec(k_E, "AES"),
						new IvParameterSpec(IV));
				byte[] m = AES.doFinal(c);
				System.out.println(R.toAddress(params) + ": " + new String(m, UTF8));
			}
		}
		System.out.println(Hex.encodeHexString(tx.bitcoinSerialize()));
	}

Don't use it, fee-calculation is not finished.

Edit: fixed