AppletTalk.com

JMecc · Guest

I am trying to encrypt a stream that I am sending from a port on one
machine to another machine (both sides using Java classes). The
standard writing across ports works:

Server:
serverSocket = new ServerSocket(port);
Socket sock = serverSocket.accept();
PrintWriter out = new PrintWriter(sock.getOutputStream(), true);
out.println("message");

Client:
Socket sock = new Socket(server, port);
BufferedReader in = new BufferedReader(new
InputStreamReader(sock.getInputStream()));
String success = in.readLine();

I am trying to RSA encrypt this stream by using the CipherInputStream &
CipherOutputStream classes:

Server:
serverSocket = new ServerSocket(port);
Socket sock = serverSocket.accept();
CipherOutputStream cos = new
CipherOutputStream(socket.getOutputStream(),cyO);
PrintWriter out = new PrintWriter(cos, true);
out.println("message");

Client:
Socket sock = new Socket(server, port);
CipherInputStream cis = new
CipherInputStream(sock.getInputStream(),cyI);
BufferedReader in = new BufferedReader(new InputStreamReader(cis));
String success = in.readLine();

I retrieve the public & private keys from files (keys are serializable
objects) and then create ciphers:
cyI = Cipher.getInstance("RSA"); //Input stream cipher to decrypt
cyI.init(Cipher.DECRYPT_MODE, privateKey);
cyO = Cipher.getInstance("RSA"); //Output stream cipher to encrypt
cyO.init(Cipher.ENCRYPT_MODE, publicKey);

the keys were originally created via KeyPairGenerator:
KeyPairGenerator KPG = KeyPairGenerator.getInstance("RSA");
KPG.initialize(1024); //Key length
KP = KPG.generateKeyPair();
priKey = (RSAPrivateKey) KP.getPrivate();
pubKey = (RSAPublicKey) KP.getPublic();

The program just hangs, so running eclipse debugging on both gets me to
the "String success = in.readLine();" line on the client, where it
blocks waiting for the server. The server has no problem running its
lines to send the data but for some reason the client does not
recognize that anything is coming in and just keeps blocking. Anyone
see what my pitfall is?
Thanks,
Jo

sgoo · Guest

Not sure, maybe the server side needs a flush after the println?

Ralf Ullrich · Guest

JMecc wrote:

JMecc · Guest

sgoo wrote:

Ralf Ullrich · Guest

JMecc wrote:

Mike Amling · Guest

Ralf Ullrich wrote:

JMecc · Guest

Thanks Ralf. I am still struggling to get this working however as I
cannot create CFB8 keys (KeyPairGenerator KPG =
KeyPairGenerator.getInstance("CFB8") Wink

. I have only successfully
created RSA ones this way (maybe there are alternative ways to create
keys). Of course with RSA keys I get to the last line of:

PrivateKey KI = Keys.readPrivate("cliPri.key");
cyI = Cipher.getInstance("DES/CFB8/NoPadding");
cyI.init(Cipher.DECRYPT_MODE, KI);

and have the error:

java.security.InvalidKeyException: No installed provider supports this
key: sun.security.rsa.RSAPrivateCrtKeyImpl
at javax.crypto.Cipher.a(DashoA12275)
at javax.crypto.Cipher.init(DashoA12275)
at javax.crypto.Cipher.init(DashoA12275)
at client.setCipher(client.java:75)
at client.<init>(client.java:55)
at client.main(client.java:17)

I guess I am not restricted to RSA, it is just the only one I've heard
of but I need some way of encrypting client-server information passage
after an initial handshake.

Thanks,
Jo

JMecc · Guest

OK so I am on my way to doing this correctly - following Ralf's
procedure:

1) Client sends RSA public key to server (unencrypted).
2) Server sends its public key back, also unencrypted (now we have
2-way RSA encrypted traffic and this works although slowly for big
files as you told me it would)
3) Client makes password string including machine data, RSA encrypts
it and sends that to the server.
4) Server verifies password and if ok, creates DES key and sends it to
client (RSA-encrypted).
5) Client decrypts this DES key, client and server make input & output
Stream*Ciphers with the DES key as initializer (this is where I am
still having a problem).
6) Any further communication is done using these Stream*Ciphers.

I didn't get how to initialize a key with a byte sequence but I found
on the web that I should be getting the parameters from my encryption
cipher using cipher.getParameters() and then pass those such that they
could be used to initialize the decryption cipher:

decrCipher.init(Cipher.DECRYPT_MODE, key, params);

The AlgorithmParameters class is not serializable though, so I use
params.getEncoded() to get a byte[], pass that over and reconstruct
params as:

params = AlgorithmParameters.getInstance("DES");
params.init(bytearray);

While this conversion performs fine within the same class, when sent
from one machine to another, trying to init a new cipher with the
recieved key and reconstructed params yields an InvalidKeyException:
Illegal Key Size.

Googling this "Illegal Key Size" universally pointed the finger at the
need for Sun's Unlimited Strength Java(TM) Cryptography Extension
Policy (bottom of http://java.sun.com/javase/downloads/index_jdk5.jsp
). I downloaded these and used them to overwrite Java's regular ploicy
files in all JRE (even within JDK) locations on both the client and
server and rebooted both machines. The error persists. I would like
to get this working before I try any triple-DES or anything more
difficult.

Anybody experience this error?
Thanks,
Jo

JMecc · Guest

Update: I got rid of the InvalidKeyException by changing:

secret = (SecretKey) cyUnwrap.unwrap(wrapped, "DES/CFB8/NoPadding",
Cipher.SECRET_KEY);

to

secret = (SecretKey) cyUnwrap.unwrap(wrapped, "DES",
Cipher.SECRET_KEY);

I'm now trying to set up the stream ciphers to see if the whole thing
works.

Jo

JMecc · Guest

OK it seems to be working fine now and man is DES faster than RSA!
Thanks a lot for the help! I was still blocking on readLine() but
changed this in favor of datainputstream.readFully() after a readInt -
I send an int stating how many bytes to expect and then the bytes
themselves. This makes everything run much smoother.

Thanks again for all the replies,
Jo