Hierarchical secret derivation with Blake2b

Documentation:

secret-tree allows deriving multiple secrets from a single seed value in a secure and forward-compatible way. The derivation procedure is hierarchical: a seed can be used to derive child seeds, which have the same functionality as the original.

Features

• Compact: the seed takes 32 bytes regardless of the number and size of derived secrets.
• Forward-compatible: it's possible to add new and/or remove existing derived secrets without regenerating the seed or littering the codebase.
• Versatile: the crate provides API to derive a virtually unbounded number of secrets (via indexing) and secrets with complex internal structure (thanks to a cryptographically secure pseudo-random number generator that can be derived from the seed).

Usage

Add this to your Crate.toml:

toml [dependencies] secret-tree = "0.4.1"

Basic usage:

```rust use secrettree::{SecretTree, Name}; use rand::{Rng, threadrng}; use secrecy::Secret;

let tree = SecretTree::new(&mut threadrng()); // Create 2 children from the tree: an ordinary secret // and a CSPRNG with a fixed seed. let secret: Secret<[u8; 32]> = tree .child(Name::new("secret")) .createsecret(); let othersecretrng = tree .child(Name::new("other_secret")) .rng(); ```

See crate documentation for more details how to use the crate.

Implementation

Blake2b is used to derive secrets in a similar (and mostly compatible) way it is used for key derivation in [libsodium]. Derived CSPRNGs are based on the [ChaCha cipher], which has been extensively studied and has much smaller state size that alternatives (~160 bytes vs several kilobytes), limiting the threat of state leakage.

Crate documentation provides more implementation details.

License

Licensed under the Apache-2.0 license.