monocypher.cr

Crystal wrapper for a cryptographic library Monocypher (Official site, Github page)

Note: Sources of Monocypher (version 4.0.1 currently) are included in the shard and will be linked statically with application. On the other hand, if libmonocypher.so is present in library paths at the time of compilation, linker seems to prefer dynamic linking.

Also included is the standard ED25519 cryptography which Monocypher supplies as an optional component.

Installation

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

dependencies:
  monocypher:
    github: konovod/monocypher

2. shards update will install a shard and compile Monocypher static library. So you need clang or gcc.

   2.1. On Windows: currently, shards way isn't supported, but you can compile monocypher manually using following commands(from visual studio development prompt):

   cd ext
   cl /c /EHsc /O2 /MT monocypher.c 
   cl /c /EHsc /O2 /MT monocypher-ed25519.c
   lib monocypher.obj monocypher-ed25519.obj
   

   and then copy monocypher.lib file to where your Crystal looks for lib files.

Usage

1. The wrapper is created with an additional requirement - using a crypto library for encrypting/decrypting of messages shouldn't cause heap allocations. So it doesn't provide function plaintext = Crypto.unlock(ciphertext, key) (as it will require allocation of plaintext every time message being decrypted). Instead it provide Crypto.decrypt(key: Bytes, input: Bytes, output: Bytes) function that will operate on preallocated buffers.
2. Most functions receive named arguments. This makes code slightly more verbose, but hopefully will prevent messing up arguments order.

Example of usage:

require "monocypher"

channel = Channel(Bytes).new # should be fixed size in real apps

alice_secret = Crypto::SecretKey.new
alice_public = Crypto::PublicKey.new(secret: alice_secret)
bob_secret = Crypto::SecretKey.new
bob_public = Crypto::PublicKey.new(secret: bob_secret)

# sender part
spawn do
  alice_shared = Crypto::SymmetricKey.new(secret1: alice_secret, public2: bob_public)
  message = "This is a test message русский текст"
  plaintext = message.to_slice
  ciphertext = Bytes.new(plaintext.size + Crypto::OVERHEAD_SYMMETRIC)
  Crypto.encrypt(key: alice_shared, input: plaintext, output: ciphertext)
  channel.send ciphertext
end

# receiver part
bob_shared = Crypto::SymmetricKey.new(secret2: bob_secret, public1: alice_public)
ciphertext = channel.receive
result = Bytes.new(ciphertext.size - Crypto::OVERHEAD_SYMMETRIC)
Crypto.decrypt(key: bob_shared, input: ciphertext, output: result)
puts String.new(result)

check spec dir for more usage examples (TODO - other examples)

Hashes

Monocypher includes functions for cryptographic hashes BLAKE2b and SHA-512, they are wrapped with simple crystal functions

Crypto.sha512("".to_slice).hexstring
# "cf83e1357eefb8bdf1542850d66d8007d620e4050b5715dc83f4a921d36ce9ce47d0d13c5d85f2b0ff8318d2877eec2f63b931bd47417a81a538327af927da3e"

Crypto.blake2b("abc".to_slice, key: "".to_slice, hash_size: 64).hexstring
# same as Crypto.blake2b("abc".to_slice).hexstring
# ba80a53f981c4d0d6a2797b69f12f6e94c212f14685ac4b74b12bb6fdbffa2d17d87c5392aab792dc252d5de4533cc9518d38aa8dbf1925ab92386edd4009923

There is also Digest interface used in Crystal stdlib:

  digest = Crypto::Digest::SHA512.new
  digest << "123"
  digest.final.hexstring  # "3c9909afec25354d551dae21590bb26e38d53f2173b8d3dc3eee4c047e7ab1c1eb8b85103e3be7ba613b31bb5c9c36214dc9f14a42fd7a2fdb84856bca5c44c2"

  digest = Crypto::Digest::BLAKE2b.new(key: "".to_slice, hash_size: 64)
  digest << "123"
  digest.final.hexstring  # "ba80a53f981c4d0d6a2797b69f12f6e94c212f14685ac4b74b12bb6fdbffa2d17d87c5392aab792dc252d5de4533cc9518d38aa8dbf1925ab92386edd4009923"

Development status

Lowlevel wrapper currently covers all of Monocypher 4.0.1 release and can be called directly.

Highlevel wrapper status:

|Area | Status | Comment | |-----|--------|---------| | Constant Time Comparison | Not planned | Already in stdlib: see https://crystal-lang.org/api/1.7.2/Crypto/Subtle.html | | Memory Wipe | Done | | | Authenticated Encryption | Partially done | TODO - streaming interface | | Blake2b Hash | Done | | | SHA-512 hash | Partially done | TODO - hkdf mode | | Password Key Derivation | Partially done | TODO - expose additional options in high-level interface | | X25519 Key Exchange | Partially done | TODO - Generating pair | | Public Key Signatures | Partially done | TODO - XEdDSA implementation | | Ed25519 | Done | | | ChaCha20 | - | Is high-level wrapper needed? | | Poly1305 | - | Is high-level wrapper needed? | | Elligator | - | Is high-level wrapper needed? |

Other planned features:

• [ ] Inline docs for everything
• [ ] Input size checking everywhere