14 KiB

Crystal CI GitHub release GitHub commits since latest release (by date) for a branch Docs

Crystal bindings for the libsodium API


  • Provide the most commonly used libsodium API's.
  • Provide an easy to use API based on reviewing most other libsodium bindings.
  • Test for compatibility against other libsodium bindings to ensure interoperability.
  • Always provide a stream interface to handle arbitrarily sized data when one is available.
  • Drop in replacement classes compatible with OpenSSL::{Digest,Cipher} when possible.
  • Use the newest system packaged libsodium or download the most recent stable version without manual configuration.


☑ Indicate specs are compared against test vectors from another source.

Several features in libsodium are already provided by Crystal:

What should I use for my application?

Only use CryptoBox::SecretKey Sign::SecretKey Aead::XChaCha20Poly1305Ietf SecretBox I don't know much about crypto.
Sodium::CryptoBox::SecretKey .box I want to encrypt + authenticate data using public key encryption.
Sodium::CryptoBox::SecretKey .encrypt I want anonymously send encrypted data. (No signatures)
Sodium::Sign::SecretKey I want to sign or verify messages. (No encryption)
Sodium::Cipher::Aead::XChaCha20Poly1305Ietf (new applications) Sodium::SecretBox (compatibility with older applications) I have a shared key and want to encrypt + authenticate data.
Sodium::Cipher::Aead::XChaCha20Poly1305Ietf I have a shared key and want to encrypt + authenticate data and authenticate additional plaintext data.
Sodium::Cipher::SecretStream I have a shared key and want encrypt + authenticate streamed data.
Sodium::Digest::Blake2b I want to hash data fast and securely.
Sodium::Digest::SipHash I want to hash data really fast and less securely. (Not implemented yet)
Sodium::Password::Hash I want to hash a password and store it.
Sodium::Password::Key I want to derive a key from a password.
Sodium::Kdf I have a high quality master key and want to make subkeys.
Sodium::Cipher::Chalsa What goes with guacamole?
Everything else I want to design my own crypto protocol and probably do it wrong.


Optionally Install libsodium. A recent version of libsodium is automatically downloaded and compiled if you don't install your own version.

Add this to your application's shard.yml:

    github: didactic-drunk/


See examples for help on using these classes in a complete application.

The specs provide the best examples of how to use or misuse individual classes.

### CryptoBox authenticated easy encryption
require "sodium"

data = "Hello World!"

# Alice is the sender
alice =

# Bob is the recipient
bob =

# Precompute a shared secret between alice and bob.
box = bob.public_key

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

# Precompute within a block.  The shared secret is wiped when the block exits. alice.public_key do |box|
  # Decrypt the message using Bob's secret key, and verify its signature against
  # Alice's public key
  decrypted = box.decrypt encrypted, nonce: nonce # => "Hello World!"

Unauthenticated public key encryption

data = "Hello World!"

# Bob is the recipient
bob =

# Encrypt a message for Bob using his public key
encrypted = bob.public_key.encrypt data

# Decrypt the message using Bob's secret key
decrypted = bob.decrypt encrypted # => "Hello World!"

Public key signing

message = "Hello World!"

secret_key =

# Sign the message
signature = secret_key.sign_detached message

# Send secret_key.public_key to the recipient

# On the recipient
public_key = key_bytes

# raises Sodium::Error::VerificationFailed on failure.
public_key.verify_detached message, signature

Secret Key Encryption

box =

message = "foobar"
encrypted, nonce = box.encrypt message

# On the other side.
box = key
message = box.decrypt encrypted, nonce: nonce


key = Sodium::Digest::Blake2B::KEY_SIZE
salt = Sodium::Digest::Blake2B::SALT_SIZE
personal = Sodium::Digest::Blake2B::PERSONAL_SIZE
out_size = 64 # bytes between Sodium::Digest::Blake2B::OUT_SIZE_MIN and Sodium::Digest::Blake2B::OUT_SIZE_MAX
data = "data".to_slice

# output_size, key, salt, and personal are optional.
digest = out_size, key: key, salt: salt, personal: personal
digest.update data
output = d.hexfinal

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

Key derivation

kdf =

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

Password based keys

pwcreate =

# Take approximately 1 second to derive a key.
pwcreate.tcost = 1.0

pass = "1234"
key, params = pwcreate.create_key pass
# Store `params` or `params.to_h` for later.

# Derive the same key from the stored params.
pwkey = Sodium::Password::Key.from_params params.to_h
key = pekey.derive_key pass

Password Hashing

pwhash =

pwhash.mem = Sodium::Password::MEMLIMIT_MIN
pwhash.ops = Sodium::Password::OPSLIMIT_MIN

pass = "1234"
hash = pwhash.create pass
pwhash.verify hash, pass

Use examples/ to help choose ops/mem limits.

Example output: Ops limit →

1 4 16 64 256 1024 4096 16384 65536 262144 1048576
8K 0.542s 2.114s
32K 0.513s 2.069s
128K 0.530s 2.121s
512K 0.566s 2.237s
2048K 0.567s 2.290s
8192K 0.670s 2.542s
32768K 0.684s 2.777s
131072K 0.805s 3.106s
524288K 0.504s 1.135s 3.661s
2097152K 2.119s


  1. Fork it ( )
  2. Install a formatting check git hook (ln -sf ../../scripts/git/pre-commit .git/hooks)
  3. Create your feature branch (git checkout -b my-new-feature)
  4. Commit your changes (git commit -am 'Add some feature')
  5. Push to the branch (git push origin my-new-feature)
  6. Create a new Pull Request

Project History

  • Originally created by Andrew Hamon
  • Forked by Didactic Drunk for lack of updates in the original project.
  • Complaints about the name being too controversial. Project name changed from "cox" to a more libsodium related name of "salty seaman".
  • ~50% complete libsodium API.
  • More complaints about the name. Dead hooker jokes added.
  • None of the original API is left.
  • More complaints threatening a boycott. Told them "Go ahead, I own Coca Cola and Water".
  • Account unsuspended.
  • Unrelated to the boycott the project name changed to "libsodium" because sodium happens to be a tasty byproduct of the two earlier names.
  • Account unsuspended.
  • Dead hooker jokes (mostly) removed.