1. http Web Authentication Web authentication is used to verify a users identity before allowing access to certain web pages On web browsers you get a login prompt There are two types of authentication: Basic and Digest

2. How Basic Authentication Works GET /protected/index.html HTTP/1.1 HTTP/1.1 401 Unauthorized WWW-Authenticate: Basic realm=“Private” GET /protected/index.html HTTP/1.1 Authorization: Basic JAadf0987awe Display Login panel

3. Problems with Basic Authentication Passwords are easy to intercept Passwords are trivial to decrypt Once you have the password you have access to many documents

4. How Digest Authentication Works GET /protected/index.html HTTP/1.1 HTTP/1.1 401 Unauthorized WWW-Authenticate: Digest realm=“Private” nonce=“897sgkjhsadAdsiu” GET /protected/index.html HTTP/1.1 Authorization: Digest username=“Alice” realm=“Private” nonce=“897sgkjhsadAdsiu” response=“5ijasd9734kuyasds0g” Display Login panel

5. Challenge and Response Challenge (nonce): any changing string –E.g. MD5(IP address:timestamp:server secret) Response: challenge hashed with the user’s name & password and uri of requested page –MD5(MD5(name:realm:password):nonce:MD5(request )) Server-specific implementation options –One time nonce –Time-stamped nonce

6. Digest Advantage over Basic Password is not transmitted in a way that can be decrypted Can’t replay the client/server handshake because the nonce changes each time The intercepted response is valid only for a single web page because the response has the request hashed. Disadvantages –Few web browser supports it Shared disadvantages –The document itself can be sniffed!!!

7. Secure Socket Layer (ssl) The secure socket layer sandwiches itself between the transport layer and the application layer in the OSI model The ssl provides: –data encryption Can the message be snooped? –server authentication Is the machine your connected to the REAL server? –message integrity Was the message manipulated between you and the server? –Optionally client authentication (seldom used) Is the server sending data to a machine that should get the data?

8. “Are you Bob?” {“Are you Bob?”} Bobs-private-key Decrypt Bob’s Public Key Problem: It’s never a good idea to encrypt anything someone sent you with your private key

9. “Are you Bob?”hash {“Are you Bob?”} {hash} Bobs-private-key “Are you Bob?” Decrypt Bob’s Public Key hash {“Are you Bob?”} & compare This method is know as a digital signature Problem: Bob is still encrypting something sent to him

10. Are you bob? Alice, this is bob (random) hash {Alice, this is bob} {hash} Bobs-private-key Decrypt {hash} Bob’s Public key hash {Alice, this is bob} compare Problem: Any one can be Bob. Where did Alice get Bob’s public key?

11. Certificates A certificate is a way of sending public keys to end users and assure they actually belong to the sender They contain –Issuer’s name –Info about the identity for whom the certificate has been signed –Public key of the sender –Some time stamps A certificate is signed by a certificate authority –Verasign, thwarty, … Web browsers have the public keys of the certificate authority pre-installed. So, when a new certificate comes and it can be decrypted with a certificate authorities key, it can be assumed that the certificate authority guarantees the public key of the sender

12. Hi Hi, I’m bob, bob’s certificate Prove it Alice, this is bob hash {Alice, this is bob} {hash} Bobs-private-key Decrypt {hash} Bob’s Public key hash {Alice, this is bob} compare Ok bob, Here’s a secret {secret} bob’s public key Decrypt {secret} Bob’s private key {Some message, hash{message}} Secret-key Decrypt {message,hash} hash {message} Compare hashs

13. Advantages of SSL Confidential session Server authentication GUI clues for users Built into most browsers Easy to configure on the server Protocol has been analyzed extensively

14. Disadvantages of SSL Users don’t check certificates –Most don’t know what they even mean Too easy to obtain a certificate Default settings are terrible –Ssl version 2 in on –Totally insecure ciphers are included in the browsers Very little use of client-side certificates Performance hit to the server