CS255 Programming Project 1

Programming Project 1 Due: Friday Feb 8 th (11:59pm)‏ – Can use extension days Can work in pairs – One solution per pair Test and submit on Leland machines – SCPD students: get SUNet ID! sunetid.stanford.edu

Overview Build a password manager Effectively a secure, networked map Works like OS keychain Client-server model Written in Java using JCE

Security Features Passwords cannot be stolen – Not even if the server is compromised Network attackers can't tamper – Can't impersonate the server either Master password can be changed – Shouldn't require reciphering everything

What is provided? Most of the application – GUI – Server – IO layer – Layered Map API – Simple test cases Skeleton code – AES – Secure network code

GUI Simple, unpolished SWT – List of resource names – Create new RN/password with ^N – Edit password with ENTER – Delete password with DEL – Change master password – Only connects to localhost Improvements welcome – Not required by any means

Server (Mostly-) atomic file store Backed by the filesystem – More transparent than a database Doesn't know anything about crypto Sets master password = 'passw0rd' – Change it in the GUI

IO Layer Probably a sign that I don't know Java IO for blobs – byte[] and byte[][] – Uses simple length encoding – Filesystem instance for server – Network instance for client/server – Secure network instance... write me!

Layered Maps Store byte[] -> byte[] maps on disk Export them over the network Encrypt and MAC them Use them as String -> String maps

Skeleton Crypto Code Wrapper around HMAC-SHA1 Catches exceptions – Most of them statically can't be thrown – Probably a few of them can (BUGS!)‏ Provides a more functional interface

Quirks in the code I'm not a Java programmer byte[] is usually assumed immutable Needs testing on Windows – GUI code – Atomic file operations There are definitely bugs

What needs to be done Aes class – AES-CTR mode – Authenticate with HMAC-SHA1 SecureBlobIO class – Negotiate secure network connection – Prevent attacker from faking commands – Watch out for replay attacks! – Store necessary parameters on disk – Recover master AES key

Errata You are NOT required to: – protect integrity of keys from compromised server – protect secrecy of keys from anyone

Security Don’t use the same key to encrypt and MAC !!! Use a common key, K, and derive encryption and MAC keys, K enc, K mac using a PRF – K enc = HMAC(K, “encrypt”); – K mac = HMAC(K, ”integrity”);

Counter Mode You must implement it. To get a “plain” cipher use ECB mode with no padding – Warning! CBC mode used by default – Need to specify “AES/ECB/NoPadding” Need a counter (try BigInteger)‏

Java Cryptography Extension Implementations of crypto primitives Cipher Pseudo-random Generator SecureRandom Message Authentication Code Mac Cryptographic Hash MessageDigest

JCE: Generating Random Keys 1.Start the PRG (random seed set by default)‏ 2.Initialize KeyGenerator with the PRG 3.Generate the key // Generate a random encryption key SecureRandom prng = SecureRandom.getInstance("SHA1PRNG"); KeyGenerator enckeygen = KeyGenerator.getInstance("AES"); enckeygen.init(prng); SecretKey enckey = enckeygen.generateKey();

JCE: Keys From Byte Data Use SecretKeySpec – Extends SecretKey // Use KeyTree API to get key bytes from password byte[] keyBytes = KeyTree.createAESKeyMaterial(passwd); // Use the bytes to create a new SecretKey SecretKeySpec keySpec = new SecretKeySpec(keyBytes, “AES”);

JCE: Using Ciphers 1.Select the algorithm 2.Initialize with desired mode and key 3.Encrypt/Decrypt // Create and initialize the cipher Cipher cipher = Cipher.getInstance("AES/ECB/NoPadding"); cipher.init(Cipher.ENCRYPT_MODE, enckey); // Encrypt the message byte [] msg = "Content is here.".getBytes(); byte [] enc = cipher.doFinal(msg); Mac class has a similar API

Grading Security comes first – Design choices – Correctness of the implementation Did you implement all required parts? Secondary – Cosmetics – Coding style – Efficiency

Submitting README file – Names, student IDs – Describe your design choices Your sources Use /usr/class/cs255/bin/submit from a Leland machine

Stuck? Use the newsgroup (su.class.cs255)‏ – Best way to have your questions answered quickly TAs cannot: – Debug your code – Troubleshoot your local Java installation