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Tony BrettOUCS Course Code ZAB 9 February 2004 E-Mail Security – Encryption and Digital Signatures Tony Brett Oxford University Computing Services February.

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Presentation on theme: "Tony BrettOUCS Course Code ZAB 9 February 2004 E-Mail Security – Encryption and Digital Signatures Tony Brett Oxford University Computing Services February."— Presentation transcript:

1 Tony BrettOUCS Course Code ZAB 9 February 2004 E-Mail Security – Encryption and Digital Signatures Tony Brett Oxford University Computing Services February 2004

2 Tony BrettOUCS Course Code ZAB 9 February 2004 Agenda What and why? PGP Keys and key pairs Encrypting messages Signing messages Verifying keys – key signing Installation on windows XP and exercise

3 Tony BrettOUCS Course Code ZAB 9 February 2004 What and Why? E-mail is not secure –as easy to fake E-mail as a typed letter. –Anyone can read it on the network. How to know you are who you say you are? Ways to secure E-mail –Digital signatures –Encryption Secure transactions

4 Tony BrettOUCS Course Code ZAB 9 February 2004 PGP – Pretty Good Privacy 1976 – Diffie/Hellman. 1977 – Rivest/Shamir/Adleman. 1991 – Zimmermann writes PGP. Send E-mail securely to a known recipient. Digitally sign E-mail so that the recipient(s) can be sure it is from you. Can also be used with file transfers. Similar is used for secure web pages.

5 Tony BrettOUCS Course Code ZAB 9 February 2004 Keys and Key Pairs Encryption is a way of changing something to something else. –e.g. simple 3-letter shift. –tony brett becomes wrqb euhww. But the recipient has to know the “key”. –How do you tell them securely? Asymmetric keys are the answer! Public/Private keys. –“Fingerprint” for verification –Pass phrase on private for security –Include E-mail address(es)

6 Tony BrettOUCS Course Code ZAB 9 February 2004 Where do I find someone’s key? (and publicise mine) Key Servers or Personal Web Pages

7 Tony BrettOUCS Course Code ZAB 9 February 2004 Encrypting Messages Use recipient's public key. Then only they can decrypt it. Can encrypt to several if more than one recipient. Then any one private key can decrypt message. No guarantee it is from you, but only they can read it.

8 Tony BrettOUCS Course Code ZAB 9 February 2004 Signing Messages Use your own private key. So long as recipient is sure they have your key they can be sure the message came from you. Your public key is widely available

9 Tony BrettOUCS Course Code ZAB 9 February 2004 For the Paranoid…. Encrypt the message with recipient’s public key and sign with your own private key. Then it’s verifiably from you and you can be sure only they can read it!

10 Tony BrettOUCS Course Code ZAB 9 February 2004 How do you know this key is mine? Anyone could generate a key for anyone else. Signing a key confirms that it belongs to the right person. –Verify identity by voice, passport, driving licence etc. –Use fingerprint to make sure you have the right one. Creates chain of trust. Key signing events do happen –http://www.ox.compsoc.net/compsoc/events/pgp-keysigning.html

11 Tony BrettOUCS Course Code ZAB 9 February 2004 How to Install PGP on Windows Download from: http://www.pgp.com/products/freeware.html Note License Restrictions Extract PGP8.EXE from ZIP file

12 Tony BrettOUCS Course Code ZAB 9 February 2004 Installation

13 Tony BrettOUCS Course Code ZAB 9 February 2004 Installation Choose to create keys and set install directory – defaults are fine!

14 Tony BrettOUCS Course Code ZAB 9 February 2004 Select Components

15 Tony BrettOUCS Course Code ZAB 9 February 2004 Finish install and restart computer

16 Tony BrettOUCS Course Code ZAB 9 February 2004 Creating your key pair Run PGP Keys. Choose “New Key” from “Keys”. You’ll need name and E-mail.

17 Tony BrettOUCS Course Code ZAB 9 February 2004 The Passphrase is VITAL! It’s your only protection from others using your private key!

18 Tony BrettOUCS Course Code ZAB 9 February 2004 Key gets generated

19 Tony BrettOUCS Course Code ZAB 9 February 2004 Exercises Send public key to a server. Try using the clipboard encryption facility Keep your private key safe and passphrase protected. –You can’t revoke a key without the private key. Get public key for tony.brett@oucs.ox.ac.uk and try to send me an encrypted message Get your public key signed.

20 Tony BrettOUCS Course Code ZAB 9 February 2004 Resources http://www.oucs.ox.ac.uk/email/secure.html http://www.pgpi.org/ http://www.pgpi.org/doc/faq/ http://users.ox.ac.uk/~aesb/pgp.ppt

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