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NaCl

A library that wraps part of djb's NaCl “networking and cryptography” library.

Find out more about that project at nacl.cace-project.eu.

Prerequisites

This library requires MRI Ruby 1.8 or 1.9. It should work anywhere where NaCl compiles (most UNIXes).

You must first install the NaCl C library before installing the gem. If you use homebrew on OS X, this is as simple as:

brew install nacl

Install

gem install nacl

How To Use

Public-key Authenticated Encryption

Want to provide authenticated encryption? Easy:

alice_pub, alice_sec = NaCl.crypto_box_keypair
bob_pub, bob_sec = NaCl.crypto_box_keypair

# Alice and Bob exchange their public keys.
# Now Alice can make a message for Bob:

nonce = SecureRandom.random_bytes(NaCl::BOX_NONCE_LENGTH)
ciphertext = NaCl.crypto_box("Meet me at the park at midnight", nonce, bob_pub, alice_sec)

# Alice then sends [ciphertext, nonce] to Bob and he can decrypt:

NaCl.crypto_box_open(ciphertext, nonce, alice_pub, bob_sec) # => "Meet me at the park at midnight"

Public-key Authentication

Just want to sign the text, but not encrypt it? No problem:

alice_pub, alice_sec = NaCl.crypto_sign_keypair

# Alice sends Bob her public key.
# Now Alice can make a message for Bob:

signed_text = NaCl.crypto_sign("Meet me at the park at midnight", alice_sec)

# Alice then sends [signed_text, nonce] to Bob and he can validate the signature:

NaCl.crypto_sign_open(signed_text, alice_pub) # => "Meet me at the park at midnight"
NaCl.crypto_sign_open(signed_text.gsub("park", "bus stop"), alice_pub) # raises NaCl::OpenError

Secret-key Authenticated Encryption

Secret key encryption requires that the two parties share a key beforehand using some secure channel.

key = SecureRandom.random_bytes(NaCl::SECRETBOX_KEY_LENGTH)

# Alice and Bob share the key by some secure means.
# Now Alice can make a message for Bob:

nonce = SecureRandom.random_bytes(NaCl::BOX_NONCE_LENGTH)
ciphertext = NaCl.crypto_secretbox("Meet me at the park at midnight", nonce, key)

# Alice then sends [ciphertext, nonce] to Bob and he can decrypt:

NaCl.crypto_secretbox_open(ciphertext, nonce, key) # => "Meet me at the park at midnght"

Licence

This wrapper library licensed under the MIT licence. Copyright 2012 Roger Nesbitt.

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