# cox
[![Build Status](https://travis-ci.org/andrewhamon/cox.svg?branch=master)](https://travis-ci.org/andrewhamon/cox)

Crystal bindings for the [libsodium box API](https://download.libsodium.org/doc/public-key_cryptography/authenticated_encryption.html)

Given a recipients public key, you can encrypt and sign a message for them. Upon
receipt, they can decrypt and authenticate the message as having come from you.

## Installation

**[Install libsodium](https://download.libsodium.org/doc/installation/)**, then:

Add this to your application's `shard.yml`:

```yaml
dependencies:
  cox:
    github: andrewhamon/cox
```

## Usage

```crystal
require "cox"

data = "Hello World!"

# Alice is the sender
alice = Cox::KeyPair.new

# Bob is the recipient
bob = Cox::KeyPair.new

# Encrypt a message for Bob using his public key, signing it with Alice's
# secret key
nonce, encrypted = Cox.encrypt(data, bob.public, alice.secret)

# Decrypt the message using Bob's secret key, and verify its signature against
# Alice's public key
decrypted = Cox.decrypt(encrypted, nonce, alice.public, bob.secret)

String.new(decrypted) # => "Hello World!"
```

## Public key signing
```crystal
message = "Hello World!"

signing_pair = Cox::SignKeyPair.new

# Sign the message
signature = Cox.sign_detached(message, signing_pair.secret)

# And verify
Cox.verify_detached(signature, message, signing_pair.public) # => true
```

## Secret Key Encryption
```crystal
key = Cox::SecretKey.random

message = "foobar"
encrypted, nonce = key.encrypt_easy message

# On the other side.
key = Cox::SecretKey.new key
message = key.decrypt_easy encrypted, nonce
```

## Blake2b
```crystal
key = Bytes.new Cox::Blake2B::KEY_SIZE
salt = Bytes.new Cox::Blake2B::SALT_SIZE
personal = Bytes.new Cox::Blake2B::PERSONAL_SIZE
out_size = 64 # bytes between Cox::Blake2B::OUT_SIZE_MIN and Cox::Blake2B::OUT_SIZE_MAX
data = "data".to_slice

# output_size, key, salt, and personal are optional.
digest = Cox::Blake2b.new out_size, key: key, salt: salt, personal: personal
digest.update data
output = d.hexdigest

digest.reset # Reuse existing object to hash again.
digest.update data
output = d.hexdigest
```

## Key derivation
```crystal
kdf = Cox::Kdf.new

# kdf.derive(8_byte_context, subkey_size, subkey_id)
subkey1 = kdf.derive "context1", 16, 0
subkey2 = kdf.derive "context1", 16, 1
subkey3 = kdf.derive "context2", 32, 0
subkey4 = kdf.derive "context2", 64, 1
```

## Password Hashing
```crystal
pwhash = Cox::Pwhash.new

pwhash.memlimit = Cox::Pwhash::MEMLIMIT_MIN
pwhash.opslimit = Cox::Pwhash::OPSLIMIT_MIN

pass = "1234"
hash = pwhash.hash_str pass
pwhash.verify hash, pass
```

## Contributing

1. Fork it ( https://github.com/andrewhamon/cox/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

## Contributors

- [andrewhamon](https://github.com/andrewhamon) Andrew Hamon - creator, maintainer
- [dorkrawk](https://github.com/dorkrawk) Dave Schwantes - contributor