Encrypting E-mail with GnuPG, Thunderbird and Enigmail

On Monday, 2 December 2013 I'm giving a presentation at KWLUG on Encrypting E-mail with GnuPG, Thunderbird and Enigmail which will be followed by a Formal Keysigning.

I'm using this page to develop my presentation notes. If you have comments, criticisms, or suggestions please put them on the Talk page.

--Bob.

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I've started to convert this page to presentation slides BobJonkman 19:52, 19 November 2013 (UTC)

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Intro to Crypto

Why use Encrypted E-mail?

• Security
  • Encrypted mail cannot be read by a Man In The Middle (MITM)
• Authenticity (Integrity)
  • Signed mail cannot be modified in transit, accidentally by mis-configured servers, or maliciously by MITM
• Non-repudiability
  • Signed mail can only come from the sender

Why NOT use Encrypted E-mail?

Rubber Hose Cryptanalysis (using a $5 wrench). http://xkcd.com/538

• Need the other party to use the same encryption
• Locked-in format
  • Lose your secret key, lose your mail
  • Need to keep revoked keys to read old mail
  • If your key is compromised, all your old mail is compromised (no forward secrecy)
• Non-repudiability
  • Politicians? CEOs?
• Rubber Hose Cryptanalysis (or $5 Wrench Cryptanalysis)
• It's hard!
  • and looks geeky...

Unencrypted, unsigned message

Date: Mon, 25 Nov 2013 18:27:22 -0500
From: Crypto Guy <cryptoguy@sobac.com>
To: Crypto Guy <cryptoguy@sobac.com>
Subject: Hello!

Hello World!

Unencrypted, signed message

Date: Mon, 25 Nov 2013 18:27:22 -0500
From: Crypto Guy <cryptoguy@sobac.com>
To: Crypto Guy <cryptoguy@sobac.com>
Subject: Hello!

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hello World!


-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.14 (GNU/Linux)
Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/

iQEcBAEBAgAGBQJSk9zaAAoJENrSxFs55fZVAAgIAK2BKzV/qUTXCu0gEWJq2U3z
mZ6nsfzjs8aXJe8CT/c7kr7HSgSV57kvukIbvcUP5sCGwpIfwK04qA0Af4J9jXp7
Wq1/k0wjA1WzhCWUEEjdBs/05bAbQ78ulTbhFlII2ywLgH6BYxgjceZa9abgF8Di
xHkRWEAI6q+scoEhi0rCGlCX3UX/pkiZ1GlaxxxMBu1J5DbFaAJZ1MiPUDOLQN9w
5LzIqi4rKTtnCQo6G3WWRg5HvPMHHmUJoaZfZpnPrszf4ttG0vrFLxJKUqZszDyr
V5Lx/IjKAZBwoRRjfpRZILFHWoveaw5MG8487jM76W7LiVTEsX2AFGI3R6uy+KA=
=0p58
-----END PGP SIGNATURE-----

Encrypted, signed message

Date: Date: Mon, 25 Nov 2013 18:27:22 -0500
From: Crypto Guy <cryptoguy@sobac.com>
To: Crypto Guy <cryptoguy@sobac.com>
Subject: Hello!

-----BEGIN PGP MESSAGE-----
Charset: ISO-8859-1
Version: GnuPG v1.4.14 (GNU/Linux)
Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/
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=jfdJ
-----END PGP MESSAGE-----

Crypto Theory

Symmetric Key Encryption

• Substitution cipher, Caesar cipher
  • Key = -1
    • Encrypt: IBM ⇒ -1 = HAL
    • Decrypt: Khmtw Trdq Fqnto ⇒ +1 = Linux User Group
  • Key = 13 (ROT13)
    • Encrypt: Linux User Group ⇒ +13 = Yvahk Hfre Tebhc
    • Decrypt: Yvahk Hfre Tebhc ⇒ +13 = Linux User Group
• Need a secure way to share key

Public/Private Key Encryption

The Math

Based on One-way function: Easy to do, hard to reverse

• 59 x 61 = ????
  • 59 x 61 = 3599
• 3551 = ?? x ??
  • 3551 = 53 x 67

The Theory

A Key Pair

Generate a keypair

• Add name, e-mail and comment (doesn't have to be your real name or e-mail)
• Public Key, Private (Secret) Key
• Anything encrypted by one key is decrypted by the other
  • Encrypt: Hello World ⇒ Public Key = |-|3110 '//0|21|)
  • Decrypt: |-|3110 '//0|21|) ⇒ Secret Key = Hello World

• Encrypt: Linux Is Cool ⇒ Secret Key = 1!/\/|_|>< !5 (001
• Decrypt: 1!/\/|_|>< !5 (001 ⇒ Public Key = Linux Is Cool

In Practice

• GnuPG/PGP uses a symmetric key, not Public/Secret keys to encrypt a message
• Symmetric Key generated by Pseudo Random Number Generator (PRNG)
• Symmetric Key is encrypted with recipient's Public Key

The Players by @0xABad1dea

• Bob encrypts a message to Alice
  • GnuPG/PGP generates a random Symmetric Key
  • Message ⇒ Symmetric Key = |\/|355463
  • Symmetric Key ⇒ Alice's Public Key = 5`/|\/||\/|37|2!( |<3`/
  • Bob sends |\/|355463 5`/|\/||\/|37|2!( |<3`/ to Alice

• Alice decrypts a message from Bob
  • Alice receives |\/|355463 5`/|\/||\/|37|2!( |<3`/ from Bob
  • 5`/|\/||\/|37|2!( |<3`/ ⇒ Alice's Secret Key = Symmetric Key
  • |\/|355463 ⇒ Symmetric Key = Message

• Bob signs a message
  • Message ⇒ Hash = ABC
  • ABC ⇒ Bob's Secret Key = 4|>(

• Alice checks Bob's signature
  • 4|>( ⇒ Bob's Public Key = ABC
  • Message ⇒ Hash = ABC
  • Same result? Message is untampered!

Practical GnuPG/PGP

• Keep your Secret Key secret!
• But you can distribute your Public Key widely
  • Upload your Public Key to keyservers
  • Send your Public Key by e-mail
• Use a Public Key to encrypt a message
  • Only that person's Secret Key can decrypt it
  • You can only encrypt a message to someone whose Public Key you have
• Use your Secret Key to sign a message
  • Anyone can use your Public Key to verify the signature
  • You can sign messages for everyone!
    • But only people who have your Public Key can verify the signature
    • Shows others that encryption is not such a weird thing
• If I download your Public Key, how do I know it's really yours?

Keysigning!

• You tell me what your Key Fingerprint is.
• I verify that's the same Key Fingerprint on your Public Key I download
• If I believe that's your Public Key, I sign it.

• Alice's Public Key ⇒ Bob's Secret Key = 5!6|>0|>
• Alice's Public Key + 5!6|>0|> = Alice's Public Key5!6|>0|>
• Alice is popular: Alice's Public Key5!6|>0|>5!6(4|2015!6|\/|41(01|\/|
  • Alice's Public Key is signed by Bob, Carol and Malcolm

Web of Trust

• Carol's Public Key has been signed by others
• Carol's Public Key5!641!(35!6|\/|41(01|\/|
  • Carol's Public Key is signed by Alice and Malcolm
• 5!641!(3 ⇒ Alice's Public Key = Carol's Public Key
  • Alice signed Carol's Public Key, ∴ Alice trusts Carol
  • Bob signed Alice's Public Key, ∴ Bob trusts Alice
  • By association, Bob trusts Carol (a little)
  • Bob also signed Malcolm's Public Key, ∴ Bob trusts Malcolm
  • Both Alice and Malcolm signed Carol's Public Key, so Bob trusts Carol (more than a little)
• Alice and Malcolm are Trusted Introducers for Carol

Demonstration

Generate keypair

If your Key Fingerprint is 04F7 742B 8F54 C40A E115 26C2 B912 89B0 D2CC E5EA

• Then your Long KeyID is 0xB91289B0D2CCE5EA
• And your Short KeyID is 0xD2CCE5EA
• Short KeyID is unique to about 1 in 10 billion (2^32)
• Long KeyID is unique to about in 10^20 (2^64)
• Key Fingerprint is unique to about 10^48 (2^160)
• Number of atoms in the universe is about 10^80

Configure Enigmail

Generally, use the defaults.

• I chose DSA for my key because of patent restrictions in 1999
• Use PGP/MIME to hide signature blocks
  • But displaying signature blocks may encourage others to use encryption
  • Some mailing lists may remove PGP/MIME signature attachments

Retrieve a Public Key

• E-mail address is convenient, but may return multiple keys
• KeyID search will return one key. Prefix KeyIDs with "0x"

Sending a Message

• OpenPGP → Default Composition Options → Signing/Encryption Options
• OpenPGP → Per-Recipient Options

Receiving a Message

How to use PGP to verify an e-mail is authentic

If you want to be extra safe, check that there's a big block of jumbled characters at the bottom.
from http://xkcd.com/1181

Fortunately, Enigmail checks a little more thoroughly!

Keysigning with Enigmail

• OpenPGP → Key Management → Edit → Sign Key

Resources

What do to with encrypted mail and who to do it with http://xkcd.com/1269

Other tools

• Evolution — Built-in support for GnuPG
• Claws — Plugins PGP/Core, PGP/Inline, PGP/MIME
• KMail — use gnupg2 package
• Mutt — Built-in support
• GMail — Use Chromium and plugin cr-gpg
• Other Webmail (Yahoo!, Hotmail, &c.) — Cut'n'paste with Firefox plugin WebPG (doesn't work for me)

Support

• KWCrypto Interest Group: http://sobac.com/kwcrypto
• PGP-Basics mailing list: http://groups.yahoo.com/neo/groups/PGP-Basics/info

• KWLUG: http://kwlug.org

IRC: irc://irc.freenode.net/kwlug

This presentation is online at http://sobac.com/KWCrypto/kwlug-2013-12-02/

Bob Jonkman

E-mail: mailto:bjonkman@sobac.com

Microblog: @bobjonkman@sn.jonkman.ca or http://sn.jonkman.ca/bobjonkman

XMPP: xmpp:bjonkman@sobac.com

Thanx to Randall Monroe for releasing XCKD comics under a CC-BY-NC 2.5 license!

The Cryptoparty keypair logo from the Cryptoparty Artwork repository on GitHub is available in the Public Domain.

The Players by Melissa Beth Elliott (@0xABad1dea on Twitter) is used with permission.

This rest of this presentation is © 2013 by Bob Jonkman and released under a CC-BY 4.0 license.