/kync_rawkey

A raw key plugin for KyNc

Primary LanguageRust

License BSD-2-Clause License MIT Travis CI AppVeyor CI

Rawkey for KyNc

This crate provides a plugin for KyNc which derives a salted AEAD key from a high entropy user secret and seals the secret using the derived AEAD key and a random nonce.

Why Rawkey

Rawkey is useful if you have already have a (static) high-entropy secret that you want to use to protect your secret. Since Rawkey does not perform any kind of password strengthening for the user secret, it MUST NOT be used with normal passwords.

Algorithm

  1. Create a secure random 16 byte Blake2b-KDF salt and a secure random 12 byte ChachaPoly-IETF nonce
  2. Derive a ChachaPoly-IETF aead_key by using the Blake2b-KDF with the user_secret as key and salt as salt
  3. Seal secret using ChachaPoly-IETF with aead_key as key and nonce as nonce

Pseudocode:

// Create a random salt and key
uint8_t salt[16], nonce[12];
secure_random(salt);
secure_random(nonce);

// Derive the AEAD key
uint8_t aead_key[32];
blake2b_kdf(aead_key, /* The secret to derive the key from: */ user_secret, salt);

// Seal the key
uint8_t capsule[sizeof(key) + 16];
chachapoly_ietf(capsule, /* Secret to protect: */ secret, aead_key, nonce);

Format

The capsule format is a simple concatenation of the salt, nonce, ciphertext and the authentication tag (|| denotes concatenation):

salt[16] || nonce[12] || chacha_ciphertext* || poly_tag[16]

Build

Prerequisites: A working Rust toolchain >= 1.39 and a unix-like make environment.

To build, test and install the library, use make, make check and make install respectively. To add additional cargo-flags, use the CARGO_FLAGS environment variable for your make invocation.