Victor Norman IS333 CS332 Spring 2014 Problem Need to be able to do secure transactions across a public network The data in the message needs to be encrypted so that no maninthemiddle can intercept it ID: 258025
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Slide1
Encryption / Security
Victor Norman
IS333 / CS332
Spring 2014Slide2
Problem
Need to be able to do secure transactions across a public network.
The data in the message needs to be encrypted so that no “man-in-the-middle” can intercept it.
Each endpoint needs to be able to
authenticate
that the other endpoint is who it says it is.Slide3
Terminology
Plaintext
Cyphertext
Encryption key
Decryption key
Asymmetric encryptionSlide4
Public Key Encryption
Each network “entity” generates a pair of keys – a private key and public key.
The private key is never shared. The public key is shared.
The private key can decrypt a message encrypted with the public key,
and vice versa.Slide5
PKE and Security
Can use public and private keys to get security problem:
sender gets the receiver’s public key.
sender encrypts the message with it, and sends to receiver (as
cyphertext
).
receiver decrypts with own private key.
Anyone can encrypt, but only the receiver can decrypt.
First problem solved.Slide6
Digital Signatures
Ensure some message is from who they say it is from.
Use own private key to encrypt message.
Only your public key can be used to decrypt
So, message must be from you.Slide7
Combine them both
To ensure privacy and authentication, combine both techniques:
1. encrypt plaintext with sender private key.
2. encrypt result with receiver public key.
3. send message.
All problems solved!
Not!Slide8
One more problem…
Before all this, each endpoint has to get the other endpoint’s public key.
What if someone in the middle intercepts the request and sends its public key as if it were the other endpoint’s public key.
Need a way to know that an endpoint’s public key really belongs to that endpoint.
Need a CA – Certificate Authority.Slide9
Certificate Authority
A state-certified repository for network entities’ public keys.
Has its own public key, too.
Its location is built into web browsers
Sender sends message to CA encrypted with CA’s public key, asking for other endpoint’s public key.
Only the endpoints can decrypt, so message is secure.
Receiver’s public key is guaranteed to be authentic, if the CA can be trusted.