SSL Protocol: Secure Transactions over the Internet, Slides of Computer Science

Download SSL Protocol: Secure Transactions over the Internet and more Slides Computer Science in PDF only on Docsity!

Part 3  Protocols 1

Secure Socket Layer

Part 3  Protocols 2

Socket layer

 “Socket layer”

lives between

application

and transport

layers

 SSL usually

lies between

HTTP and TCP

application

transport

network

link

physical

Socket “layer” OS

User

NIC

Part 3  Protocols 4

Simple SSL-like Protocol

Alice Bob

I’d like to talk to you securely

Here’s my certificate

{KAB}Bob

protected HTTP

 Is Alice sure she’s talking to Bob?

 Is Bob sure he’s talking to Alice?

Part 3  Protocols 5

Simplified SSL Protocol

Alice Bob

Can we talk?, cipher list, RA certificate, cipher, RB {S}Bob, E(h(msgs,CLNT,K),K)

Data protected with key K

h(msgs,SRVR,K)

 S is pre-master secret

 K = h(S,RA,RB)

 msgs = all previous messages

 CLNT and SRVR are constants

Part 3  Protocols 7

SSL Authentication

 Alice authenticates Bob, not vice-versa

o How does client authenticate server? o Why does server not authenticate client?

 Mutual authentication is possible: Bob

sends certificate request in message 2

o This requires client to have certificate o If server wants to authenticate client, server could instead require (encrypted) password

Part 3  Protocols 8

SSL MiM Attack

Alice (^) Bob

RA

certificateT, RB {S 1 }Trudy,E(X 1 ,K 1 )

E(data,K 1 )

h(Y 1 ,K 1 )

 Q: What prevents this MiM attack?  A: Bob’s certificate must be signed by a certificate authority (such as Verisign)  What does Web browser do if sig. not valid?  What does user do if signature is not valid?

Trudy

RA

certificateB, RB {S 2 }Bob,E(X 2 ,K 2 )

E(data,K 2 )

h(Y 2 ,K 2 )

Part 3  Protocols 10

SSL Connection

Alice Bob

session-ID, cipher list, RA session-ID, cipher, RB, h(msgs,SRVR,K) h(msgs,CLNT,K) Protected data

 Assuming SSL session exists  So S is already known to Alice and Bob  Both sides must remember session-ID  Again, K = h(S,RA,RB)  No public key operations! (relies on known S)

Part 3  Protocols 11

SSL vs IPSec

 IPSec  discussed in next section

o Lives at the network layer (part of the OS) o Has encryption, integrity, authentication, etc. o Is overly complex (including serious flaws)

 SSL (and IEEE standard known as TLS)

o Lives at socket layer (part of user space) o Has encryption, integrity, authentication, etc. o Has a simpler specification