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Posted on Jul 24

Encrypting Secrets in Rust Without Writing Crypto Glue Code

#cryptography #rust #security #encryption

Every Rust developer who needs application-level encryption eventually reaches for crates like aes-gcm or chacha20poly1305. Those crates provide excellent cryptographic primitives - but building a complete encryption workflow still means deciding how to derive keys, generate nonces, encode ciphertext, and store master keys safely.

That's the problem encryptman solves.

What is encryptman?

encryptman is a Rust crate that gives you a dead-simple API for encrypting and decrypting strings - passwords, API keys, tokens, anything you'd rather not store in plaintext.

Under the hood, it uses:

AES-256-GCM for authenticated encryption (confidentiality + integrity)
HKDF-SHA256 for deriving purpose-specific keys from a single master key
Random 12-byte nonces - encrypting the same plaintext twice yields different ciphertexts
Zeroize on drop - master key memory is wiped automatically

use encryptman::{encrypt, decrypt, generate_master_key};

let master_key = generate_master_key();

let ciphertext = encrypt(&master_key, "my_database_password")?;
let plaintext = decrypt(&master_key, &ciphertext)?;

assert_eq!(plaintext, "my_database_password");

That's it. No algorithm selection. No nonce management. No encoding headaches.

Why not just use aes-gcm directly?

You absolutely can. But here's what you'll need to handle yourself:

Key derivation from a master key (HKDF setup)
Random nonce generation per encryption call
Base64 encoding for safe storage
Zeroizing key material from memory
Version byte for future algorithm migration
Context isolation to prevent cross-domain ciphertext substitution

encryptman bundles all of this into a single, well-documented API with missing_docs = "deny" enforcing complete documentation.

Context isolation

One feature that's easy to overlook: encryptman supports context strings for HKDF key derivation. Different contexts produce different subkeys from the same master key, so ciphertext from one domain can't be decrypted in another. Contexts are implemented using HKDF domain separation rather than additional encryption metadata.

use encryptman::{encrypt_with_context, decrypt_with_context, generate_master_key};

let key = generate_master_key();

// Database passwords
let db_ct = encrypt_with_context(&key, "database", "postgres://secret")?;

// API keys
let api_ct = encrypt_with_context(&key, "api-keys", "sk-12345")?;

// Same plaintext, different contexts -> different ciphertext
assert_ne!(db_ct, api_ct);

// Cross-context decryption fails
assert!(decrypt_with_context(&key, "database", &api_ct).is_err());

This prevents a whole class of attacks where an attacker swaps ciphertexts between unrelated parts of your application.

URL-safe encoding

Need to put encrypted values in JWTs, cookies, or URLs? encryptman has you covered with Encoding::UrlSafeNoPad:

use encryptman::{encrypt_with_encoding, decrypt_with_encoding, generate_master_key, Encoding};

let key = generate_master_key();

let encrypted = encrypt_with_encoding(&key, "jwt", "token", Encoding::UrlSafeNoPad)?;
let decrypted = decrypt_with_encoding(&key, "jwt", &encrypted, Encoding::UrlSafeNoPad)?;

assert_eq!(decrypted, "token");

No more worrying about + and / characters breaking your URLs.

The key storage problem

Here's where things get interesting. encryptman handles encryption beautifully, but it doesn't solve the next question: where do you store the master key?

The README says "use an OS keychain or KMS" - but that still means writing platform-specific code. This is where encryptman-keyring comes in.

encryptman-keyring: Zero file management

encryptman-keyring is a companion crate that stores the master key directly in your OS native credential store:

Platform	Credential Store
Windows	Credential Manager
macOS	Keychain
Linux	Secret Service (DBus)

One call. No key files. No .env headaches. Applications never access the raw master key directly unless they explicitly request it.

use encryptman_keyring::Vault;

// First call: generates key -> stores in OS keychain
// Later calls: loads existing key from keychain
let vault = Vault::new("my-app")?;

let encrypted = vault.encrypt("my_database_password")?;
let decrypted = vault.decrypt(&encrypted)?;

assert_eq!(decrypted, "my_database_password");

The service name ("my-app") doubles as the HKDF context, so different applications automatically get domain isolation.

The architecture looks like this:

                Application
                     |
                     v
          encryptman-keyring
                     |
      +--------------+--------------+
      v              v              v
   Windows       macOS Keychain   Secret Service
   Credential
   Manager

Multiple contexts with one vault

use encryptman_keyring::Vault;

let vault = Vault::new("my-app")?;

let db_secret = vault.encrypt_with_context("database", "postgres://...")?;
let api_secret = vault.encrypt_with_context("api-keys", "sk-12345")?;

assert_ne!(db_secret, api_secret);

let db_plain = vault.decrypt_with_context("database", &db_secret)?;

Separating environments

Need different keys for dev and production? Use new_with_target:

use encryptman_keyring::Vault;

let dev_vault = Vault::new_with_target("my-app", "development")?;
let prod_vault = Vault::new_with_target("my-app", "production")?;

Each target stores a separate key in the OS keychain under the same service name.

Migrating from key files

Already have .key files lying around? Import them and delete the originals in one step:

use encryptman_keyring::Vault;

let vault = Vault::migrate_from_file("my-app", std::path::Path::new("/path/to/.key"))?;
// File is deleted after successful migration

Typical use cases

encryptman is designed for application-level secrets such as:

Database connection strings
API keys
OAuth refresh tokens
SMTP credentials
Third-party service secrets
Local application configuration

When NOT to use these crates

encryptman is designed for encrypting small strings - passwords, API keys, tokens. It's not suited for:

Password hashing - use argon2 or bcrypt
File encryption - use a streaming encryption library instead of encrypting the whole file in memory
Database-at-rest encryption - use your database's built-in encryption (TDE, disk encryption, etc.)
Large data - the entire plaintext is held in memory

encryptman-keyring isn't ideal for:

Headless/CI environments - OS keychain may not be available
Multi-user servers - keyring entries are per-user; consider Vault or AWS Secrets Manager

The pipeline

master key
    |
    v
HKDF-SHA256("encryptman:{context}")
    |
    v
AES-256-GCM key
    |
    v
plaintext + random nonce
    |
    v
ciphertext
    |
    v
version || nonce || ciphertext
    |
    v
Base64

Key Derivation: HKDF-SHA256 generates domain-separated subkeys
Authenticated Encryption: AES-256-GCM detects any tampering
Fresh Nonce: 12 random bytes per encryption call
Version Byte: Reserved for future algorithm migrations

Final thoughts

encryptman intentionally focuses on application secrets rather than exposing low-level cryptographic primitives. If all you need is to encrypt configuration values, API tokens, or passwords, it provides a simple, opinionated API while following modern cryptographic practices.

The ecosystem covers the full workflow:

✅ AES-256-GCM authenticated encryption
✅ HKDF-SHA256 key derivation
✅ Context isolation
✅ OS keychain integration (no key files)
✅ URL-safe encoding for JWTs/cookies
✅ Zeroize on drop
✅ MSRV: Rust 1.85 (Edition 2024)

Just generate a key and start encrypting.

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