Krypton

A CLI tool for creating encrypted vaults and single-file encryption with file's metadata protection.

Krypton is also a Rust library, other software can use its encryption primitives without reimplementing AES-256-GCM or Argon2id.

Library Usage

[dependencies]
krypton = { version = "0.2", default-features = false }

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

let out = encrypt_file("password", Path::new("document.pdf"), None)?;
let name = decrypt_file("password", Path::new("out.krf"), Path::new("restored.pdf"))?;

let mut vault = Vault::new("myvault".into());
vault.init("password")?;
vault.unlock("password")?;
vault.add(Path::new("secret.pdf"), None)?;
vault.add(Path::new("photos"), None)?;
let files = vault.list()?;
vault.extract("secret.pdf", Path::new("./out"))?;
vault.change_password("password", "newpassword")?;
vault.lock();

The library exposes:

• krypton::encrypt_file / decrypt_file — single file .krf format
• krypton::Vault — multi-file encrypted vault container
• krypton::crypto — low-level AES-256-GCM + Argon2id primitives
• krypton::Error / Result — error types

CLI dependencies (clap, rpassword) are optional; library users disable them with default-features = false.

CLI Usage

Install:

cargo install krypton

Single File Mode

# Encrypt — filename hidden
krypton encrypt taxes2024.pdf
# Output: 3b736a01...431.krf (random hashed name)

# Decrypt — recovers original filename
krypton decrypt 3b736a01...431.krf output.pdf
# Decrypted 'taxes2024.pdf' to: output.pdf

Vault Mode

# Create vault
krypton init myvault

# Add files (filename hidden in vault)
krypton add myvault secret.pdf
krypton add myvault photos/

# List (shows original names — requires password)
krypton list myvault

# Extract
krypton extract myvault secret.pdf ./decrypted.pdf

# Remove
krypton remove myvault secret.pdf

# Change password
krypton change-password myvault

Password Options

# Interactive (default)
krypton encrypt file.txt

# Via environment variable
KRYPTON_PASSWORD="secret" krypton encrypt file.txt

Security Features

Encryption Standards

• Algorithm: AES-256-GCM (authenticated encryption)
• Key Derivation: Argon2id (memory-hard, GPU-resistant)
• Parameters: Argon2id with 64MB memory, 4 iterations, 4 parallelism

Metadata Protection

• Filename Encryption: All filenames are hashed and hidden
• File Content: Encrypted with unique nonces per chunk
• Key Derivation: Salt prevents rainbow table attacks
• Memory Security: Sensitive data zeroed after use

File Format (.krf)

KRYPTON2\n      # Magic header (9 bytes)
[22 bytes]      # Salt
[12 bytes]      # Nonce
[16 bytes]      # Authentication tag
[4 bytes]       # Ciphertext length
[ciphertext]    # Encrypted [filename\0content]

Filename Protection

• Original filename is encrypted inside the ciphertext
• Output filename is a random hash (e.g., 3b73...431.krf)
• No metadata leakage, even filename size is hidden
• Decryption recovers original filename automatically

Vault Structure

vault/
├── vault.config        # Encrypted master key + parameters
└── d/                  # Encrypted files
    ├── .manifest.enc   # Encrypted file index (names + metadata)
    └── [hash]/[hash].enc  # Hashed filenames — completely hidden

Vault Filename Protection

• Original filenames are hashed with master key
• Original names only visible after unlock + list command
• Even the vault owner sees clean names only when authenticated

Security Comparison

Feature	Krypton	Cryptomator	GPG	7-Zip
Content encryption	✅ AES-256-GCM	✅ AES-256-GCM	✅ AES-256	✅ AES-256
Filename hidden	✅ YES	✅ YES	❌ No	❌ No
Key derivation	✅ Argon2id	⚠️ PBKDF2	⚠️ PBKDF2	⚠️ PBKDF2

Architecture

Key Hierarchy

User Password
     │
     ▼
Argon2id(salt, password) → Derived Key
     │
     ▼
AES-256-GCM(derived_key, master_key) → vault.config
     │
     ▼
Master Key (32 bytes)
     │
     ├──► Encrypt/decrypt all vault files
     │
     └──► Hash filenames (SHA256 keyed with master key)