Krypton

A high-quality Rust library for encrypted vaults and single-file encryption with full metadata protection - built on AES-256-GCM and Argon2id.

Full technical documentation

See SECURITY for the threat model, design decisions and known limitations.

See ROADMAP for the upcoming planned work.

If you are interested in contributing to the project, contribution rules are mentioned in CONTRIBUTING.md.

Library Usage

use krypton::{encrypt_file, decrypt_file, Vault};
use std::path::Path;

// Single file: filename is encrypted inside the container.
let out = encrypt_file("correct horse", Path::new("document.pdf"), None)?;
let original_name = decrypt_file("correct horse", &out, Path::new("restored.pdf"))?;
assert_eq!(original_name, "document.pdf");

// Multi-file encrypted vault.
let mut vault = Vault::new("myvault".into());
vault.init("correct horse")?;
vault.unlock("correct horse")?;
vault.add(Path::new("secret.pdf"), None)?;
vault.add(Path::new("photos"), Some("photos"))?; // whole trees
let entries = vault.list()?;
vault.extract("photos", Path::new("./restored"))?;
vault.change_password("correct horse", "new password")?; // no re-encryption needed
vault.lock();

Public API

Module	Contents
krypton::*	encrypt_file / decrypt_file (.krf containers), Vault, EntryInfo, IntegrityReport
krypton::crypto	Low-level primitives: Key, seal/open (AAD), derive_key, HKDF subkeys, constant-time compare
krypton::kdf	KdfParams — Argon2id parameters with validation bounds
krypton::sanitize	Entry-name validation / traversal defense
krypton::error	Error, Result

Run cargo doc --open for full documentation with examples on every public item.

Security Features

• AES-256-GCM authenticated encryption for every byte of ciphertext
• Argon2id key derivation (64 MiB, t=4) with parameters stored in each container, so defaults can evolve without breaking old files
• Per-object subkeys via HKDF-SHA256 — every file gets an independent content key
• Deterministic counter nonces per chunk — eliminates random-nonce birthday collisions on large files and makes reordering detectable
• AAD everywhere — chunk index and record context are bound into each AEAD operation; truncation, splicing and extension are all detected
• Streaming — 64 KiB chunks with constant memory use; files of any size
• Metadata privacy — original filenames never appear unencrypted; .krf outputs get random hashed names
• Hardened memory — keys live in zeroizing buffers, scrubbed on drop; #![forbid(unsafe_code)]
• Crash safety — configs, manifests and plaintext outputs are written via temp file + rename; interrupted operations never leave half-written data or bricked vaults
• Traversal defense — names recovered from containers are sanitized before touching the filesystem
• One universal container format — .krf files, vault blobs and manifests share a single envelope; new object types are new payload types, never new formats

File Format

Every object is a krypton container:

"KRYPTON\0"       magic (8 bytes, never changes)
[u16 LE]          envelope version (currently 1)
[u8 kind]         key derivation:
                    0 = HKDF(master key, object salt[32])          — vault objects
                    1 = Argon2id(password, salt[32], params[12])
                        then HKDF with object salt[32]             — .krf files
[len u32][ct‖tag] …   chunk records (64 KiB plaintext each)
[00000000]        end-of-chunks marker
[len u32][ct‖tag] authenticated trailer: {type: file|directory|manifest,
                                           name?, size, chunk_count}

Header bytes are bound to key derivation; the payload type is bound into every record's AAD, so records cannot be transplanted between containers.

Vault

vault/
├── vault.config        JSON v2: wrapped master key + KDF params (atomic writes)
└── d/
    ├── .manifest.enc   encrypted index incl. directory child lists
    └── <hash>/<hash>.enc  per-entry blobs

Entry paths are derived from SHA256(master_key ‖ path); blob contents use per-entry subkeys. Directory removal deletes the entire subtree — blobs and manifest records alike.

Key Hierarchy

Password ──Argon2id(salt) -> KEK ──AES-GCM-wrap -> vault.config holds Master Key -> SHA256(master ‖ path) → blob location
                                                                    │ 
                                            HKDF(master, per-file salt) → content key
                                                                    │
                                            counter nonces + AAD(index) → AES-GCM chunks

Changing the password only re-wraps the master key — stored data is never re-encrypted.

Development

cargo test         # 55 tests: unit, integration, doc examples
cargo clippy       # clean

License

Licensed under Apache-2.0.