Santa Cruz CryptoParty


Why Cryptography Matters




"If you have nothing to hide, why be afraid?"

Literally invented by nazis

Crypto is everywhere

  • Banking
  • Secure browsing
  • The credit card chip
  • Cell phone transmissions
  • Password protected wifi

Basics of Cryptography

Throughout history, these two things have been needed by humans:

  1. The need to share information
  2. The need to protect the information they are sharing
  1. Comes from the combination of (Greek) words Krypto (hidden) and graphene (writing)
  2. The Spartans wrote on a narrow strip of parchment wrapped around a cylindrical log (called a Scytale) to encrypt messages
  1. Can be defined as: The art and science of concealing messages to introduce secrecy in information security
  2. From the Oxford dictionary: The art of writing or solving codes

Caesar's Cipher

  1. Used by the ancient Romans
  2. To encode "shift" forward the alphabet by a constant offset
  3. To decode "shift" back

Modern Cryptography

Two types:
  1. Classic
    • Manipulates letters and digits directly
    • Based on 'Security through obscurity'
  2. Modern
    • Operates on binary seqences
    • Relies on publicly known mathematical algorithms and computational difficulty

Security of Cryptography

Cryptography provides four services:

  1. Confidentiality - protects your information from an unauthorized person
  2. Data Integrity - determines if your message/communication has been tampered with
  3. Authentication - confirms that a message was sent by a known and verified sender
  4. Non-repudiation - ensures an entity cannot refuse ownership of a previous action

Secure Mobile Messaging with Signal

What is Signal?

  • Signal is a secure communication platform from Open Whisper Systems
  • Provides a secure, easy to use alternative to calling, texting, and video chat
  • Successor to RedPhone and TextSecure
  • Uses data connection instead of phone network
  • Signal seamlessly integrates with phone/SMS for the rest of your contacts

How do I use Signal to communicate?

  • Instead of calling your contact, try a Signal voice call
  • Instead of sending a text message, send it with Signal. Group chat is supported as well
  • You can also video chat (no FaceTime, Allo)
  • You can still share pictures and other media
  • For contacts without Signal, fallback to the phone network
  • Invite your friends to use Signal too!

How does Signal protect my communications?

  • Provides end-to-end encryption and authentication for text, audio, and video chat
  • Uses the Double Ratchet algorithm, developed by Trevor Perrin and Moxie Marlinspike based on trusted crypto primitives like Curve25519, AES-256, and HMAC-SHA256
  • Bunch of other cool privacy features like disappearing messages, key change alerts and verification, and local message db encryption
  • Leaves less metadata than using the phone network or other communication apps

Where can I get Signal?

  • Signal is available for mobile in the Google Play store and the Apple App Store
  • After installing, set Signal as your default SMS application for ease of use
  • Signal is also available for desktop as a Chrome app

Bitcoin & Blockchains

Internet Anonymity with Tor and i2p

What are Tor and i2p?

What are Tor and i2p?

  • Tor is an anonymous internet proxy that allows users to use the Internet
  • Invented at the Naval Research Lab, used by technologists, law enforcement, intelligence services, political activists, and more
  • Tor also allows access to onion services, accessible only over Tor
  • i2p, the Invisible Internet Project allows access to an alternative anonymous "Internet"
  • Initially released in 2003, maintained mostly by pseudonymous developers

How do Tor and i2p help?

  • Prevents a website or server from knowing your real IP address
  • Prevents your ISP from watching what you do online
  • But they do know that you're using Tor (without the use of bridges and the obfuscated pluggable transports) or i2p
  • Internet anonymity promotes democracy, free speech and free thought by allowing users to research and express themselves without fear

How do Tor and i2p work?

  • Tor uses "onion routing," multiple layers of encryption in a series of relays through a mix network
  • By default, a client tunnels through 3 encrypted hops. Each node only knows the next and previous address
  • A Tor node can be a middle relay, exit node, or onion service
  • i2p uses "Garlic routing," as multiple packets can be encapsulated into a single i2p packet

Differences between Tor and i2p

Tor i2p
Onion routing garlic routing
Proxy service private Internet
Circuit switched packet switched
TCP only supports UDP
Centralized services fully decentralized
USG funding anonymous volunteer developers

Using Tor and i2p as a client

  • Tor Browser Bundle
  • Avoid fingerprinting by blending in to the crowd
  • Tor daemon and proxy configuration
  • Useful for CLI tools and other software. See: torsocks(1), proxychains(1)
  • Tails Live CD or USB that includes Tor and i2p (for now, v2.11)
  • In-memory operating system, wiped on shutdown

Running an Onion Service

  • An onion service allows a server to be accessible over a special .onion address
  • Configure the HiddenServiceDir and HiddenServicePort directives in the torrc
  • Security considerations
  • Misconfigurations: disable server-status page
  • Vulnerabilities: command injection, server exploits
  • Timing attacks: don't run another service, don't run a relay

Running a relay, exit node / router

  • If you'd like to support the Tor network, you can run a relay or exit node
  • To run a Tor relay, configure your ORPort and ExitPolicy. For middle relay only, reject *:*
  • If you run an exit node, you may get some strange traffic originating from your address
  • You can filter most traffic that would attract attention by allowing only HTTPS (443)
  • Alternatively, be prepared to explain what Tor is, or have a lawyer to do so
  • Note: with i2p, you're a relay by default

Where to get Tor

  • Tor is available at
  • Tor Browser Bundle signing key: EF6E 286D DA85 EA2A 4BA7 DE68 4E2C 6E87 9329 8290
  • Tails is available at
  • Tails developers signing key: A490 D0F4 D311 A415 3E2B B7CA DBB8 02B2 58AC D84F
  • The Orbot Android app is available in the Google Play store
  • Install on Debian and Ubuntu Linux with
    sudo apt-get install tor

Where to get i2p

Where to get i2p

  • i2p is written in Java (cross-platform)
  • i2p is available at
  • i2p developers signing key: 2D3D 2D03 910C 6504 C121 0C65 EE60 C0C8 EE72 56A8
  • The i2p Android app is available in the Google Play store


(Pretty Good Privacy)

Text messages




Android OpenKeychain

Web of Trust


HTTPS Everywhere

  • Plugin for web browsers
  • Tries to force your browser to request web resources over HTTPS
  • Available for Chrome, Firefox and Opera

Let's Encrypt

  1. Project to grant free Domain Verified (DV) SSL certificates
  2. Free, automated and open source Certificate Authority (CA)
  3. Operated by the non-profit Internet Security Research Group (ISRG)

Let's Encrypt Cont.

  • Free: Anyone who owns a domain name can use Let’s Encrypt to obtain a trusted certificate at no cost
  • Automatic: Certbot handles creating, installing and renewing the certificate
  • Transparent: All certificates issued or revoked are available to the public
  • Secure: Promotes TLS security best practices

Transport Layer Security

(AKA Secure Sockets Layer)

What is it?

  • Protocol used for secure electronic communications
  • Designed to prevent eavesdropping and tampering
  • Used in many applications such as web browsing, email and text-messaging
  • Practical form of public key cryptography
  • Also referred to as "Secure Sockets Layer" or "SSL"

How Does it Work?

  • The communication between two devices is encrypted using a shared secret
  • The shared secret is only known to the devices communicating
  • Each message received is decrypted using a code known only to the receiver

Best Practices

  • Do not browse websites which don't have valid SSL certificates
  • Use more technology which was developed with security in mind
  • Do not use any versions of the SSL protocol, use TLS instead (preferably TLSv1.2)

Useful Technologies

KeePassX, LastPass, and YubiKey

Password Managers

  • Long Random Passwords
  • Password Diversity
  • Fights Key Loggers
  • How Passwords Are Compromised
  • Sending Passwords Via Email
  • Good Keychain Password = Passphrase


  • Onetime Passwords
  • Public Key Encryption

Secure Instant Messaging with OTR and OMEMO

What is OTR?

  • "Off The Record" messaging over instant messaging protocols like XMPP and AIM
  • Extends IM with encryption, authentication, forward secrecy, and deniable authentication
  • OTR supports file transfers (since version 3)

How do I use OTR?

  • OTR can be installed as an extension to many popular instant messaging clients, such as Pidgin
  • The Android app Xabber also supports OTR for secure instant messaging on the go
  • Many clients can be configured to automatically initiate an OTR session

How does OTR protect my communications?

  • Encrypts your communication from prying eyes
  • Based on AES-128, Diffie-Hellman, and SHA-1
  • Authenticates your communicating party
  • Provides deniable encryption

Where do I get OTR?

  • Available as a plugin for Pidgin (cross platform)
  • Natively supported by
  • Adium on OS X
  • Kopete on UNIX-like systems
  • Xabber and Conversations for Android
  • ChatSecure for iOS

What is OMEMO?

  • Next generation OTR with encrypted group chat support
  • Introduced in Google Summer of Code 2015 to Conversations for Android
  • Also offers forward secrecy and deniable encryption

How is OMEMO different than OTR?

  • Supports group chat (multi-client end-to-end encryption)
  • OMEMO uses the Double Ratchet algorithm (Signal)

Where can I get OMEMO?

  • Originally written for Conversations for Android
  • ChatSecure for iOS supports OMEMO
  • Cross-platform client Gajim supports OMEMO through a plugin

Bonus: Anonymous, encrypted messaging with Ricochet

  • Dedicated, Tor-based instant messenger
  • Use Tor onion addresses instead of usernames or nick names
  • End-to-end message encryption
  • No central servers or middle man
  • Eliminates conversation metadata
  • Soon to support file transfers (or use OnionShare)

Quantum Cryptography

Quantum changes everything

  • Quantum breaks common cryptography
  • Quantum enables new better cryptography

There are two types of traditional cryptography

  • Symmetric
  • Asymmetric


  • Encrypt and decrypt keys are the same
  • Key exchange is hard
  • Typically very fast
  • Used for encrypting data


  • Encrypt and decrypt keys are different
  • Typically very slow
  • Mostly used for encrypting symmetric encryption keys

Common Asymmetric Encryption

  • RSA
  • Depends on the assumption that factoring a product of two very large prime numbers is hard
  • Diffie–Hellman/ElGamal
  • Depends on the assumption that the discrete log problem is hard

Quantum computing breaks common cryptography

  • Shor's algorithm
  • Uses a quantum computer to efficiently factor very large numbers
  • Also works for discrete logs
  • Symmetric is thought to be mostly safe

Quantum enables new better cryptography

  • Quantum mechanics provide useful guarantees
  • It is impossible to copy data encoded in a quantum state
  • The very act of reading data encoded in a quantum state changes the state