CS 255 – Cryptography & Computer Security

Programming Project 2 – Winter 04

Priyank Patel pkpatel@cs.stanford.edu

Chat System so far…

Offline ChatAdmin

PT file

CT file

Chat Server Chat Client

Encrypt

Decrypt

Handle/username

Y/N

Encrypted Session

New SetupOffline

ChatAdmin

PT file with privileges

CT file

Online Certificate Authority

Encrypt

Decrypt

Chat Server

Chat Client 1- way authenticated

SSL Session

Password authenticate client and issue

certificate

2- way authenticated SSL Session

Room A

Room B

•Determine privileges from certificate

•Admit to the appropriate room

Requirements Secure all traffic using SSL Use X509 certificates for authentication Use password authentication only to

procure certificates Use X509 V3 extensions to provide

access control Implement a secure and efficient online

certificate revocation system (extra-credit)

Offline PKI Setup keytool – command line utility

organizes key material into keystores one keystore file for each entity initially keystore contains the

public/private key pair and a self-signed certificate

allows storage of trusted certificate entries and trusted certificate chains

Offline PKI Setup (contd..) Generate keystore for the RootCA

(verigoodsign, inc.)

keytool -genkey –alias mykey -keystore RootCA[asks a bunch of information …][similar for every other entity]

RootCA • mykey

...ChatServer

• mykey

Client_1 • mykey

Keystores

Offline PKI Setup (contd..) Everybody trusts the RootCA (verigoodsign)

keytool -export -alias mykey -file RootCA.cer -keystore RootCA

[dumps the RootCA’s self-signed certificate to disk]

keytool -import -trustcacerts -alias rootca -file RegCA.cer -keystore ChatServer

[similar for every other entity]

RootCA • mykey

...ChatServer

• mykey

• rootca

Client_1 • mykey

• rootca

Keystores

Offline PKI Setup (contd..) ChatServer public key signed by the RootCA

(create the class KeySigner) Create a new certificate for the ChatServer’s public

key, signed by the RootCA’s private key (Chat.X509CertificateGenerator)

Replace self-signed cert in “ChatServer” KS with a certificate signed by the RootCA.

java.security.KeyStore allows you to load a keystore from a file and manipulate entries in it.

ChatServer

• mykey (signed by RootCA)

• rootca

ChatServer

• mykey

• rootca

SSL – Secure Socket Layer Provides authentication (optional),

handshaking and encryption and integrity. Normally, server authenticates to the client,

but the client does not as part of the SSL setup(unless explicitly required by the server)

Once handshake has been done, symmetric encryption is used for the rest of the session.

SSL setup requires 2 steps (roughly speaking) : Trust establishment Key Generation

SSL – JSSE API

SSL – JSSE API javax.net.SSLContext – encapsulates the

information required for setting up a connection

javax.net.SSL.KeyManager Obtained from the KeyManagerFactory Initialized with the KeyStore and KeyStore password

javax.net.SSL.TrustManager Obtained from the TrustManagerFactory Initialized with the KeyStore[does not require the password – because does not require to use

the private key of the keystore]

SSL – JSSE API Client sockets : javax.net.ssl.SSLSocket

Useful way to create sockets on the client: SSLSocketFactory.createSocket(host, port);

SSLSocketFactory created from SSLContext [this call actually connects to the server running on

“host” and listening on port number “port”]

SSLSocket object also returned on a server when a remote client connects.

SSL – JSSE API Server sockets : javax.net.ssl.SSLServerSocket

Useful way to create sockets on the server: SSLServerSocketFactory.

createSocket(port); SSLServerSocketFactory created from SSLContext

Socket created in this manner is bound to the “port”.

Client authentication required or notSSLServerSocket.setNeedClientAuth(true/false)

SSL – JSSE API Server : SSLServerSocket.accept() Returns SSLSocket object on connection from

client. No SSL handshake, authentication yet.

SSLSock.handshake() : perform actual SSL handshake

throws Exception on failure can be one of several exceptions

CertificateExpiredException, CertificateParsingexception, etc.

SSL – JSSE API After successful handshake, use like normal

sockets.

Get a BufferedReader and Writer and start exchanging messages.

Every message using the socket’s I/O objects will be encrypted and checked for integrity by the underlying library

Certificate Extensions Customized v3 extensions

RoomAExtension and RoomBExtension Are true/false based on the privileges in the initial file Make sense only for the client certificates

Client can have access to either room A or room B Rejected if {true,true} or {false,false}

Certificate Extensions Where in the system do you check for

valid privileges?

At the time when the client handshakes with the server.

A question of trust? => modification required in the TrustManager

Extend the TrustManager to MyTrustManager (MTM)

Use MTM with your SSLContext on the server.

Certificate Extensions (contd..) MyTrustManager class

Override checkClientTrusted(…) Check if the client certificate has the invalid

privileges[i.e. allowed in both rooms or none]

If failure, throw CertificateException

MTM will be called by the system during the SSL handshake.

Certificate Revocation Need to add checks on the ChatServer and the

CertificateAuthority. Space-efficient.

Finally… Document succinctly but comprehensively.

(without aiming for the Pulitzer prize!)

Best of luck…