Hefesto

Double envelope encryption for multi-tenant applications. Encrypts field values with two independent keys (tenant + server master), using AES-256-GCM and Argon2id.

What it does

• Field encryption — encrypt sensitive DB fields (emails, names, documents) with per-tenant isolation
• Password hashing — one-way Argon2id hashes, not reversible
• Lookup hashing — deterministic HMAC-SHA256 so you can WHERE email_lookup = ? without decrypting

What it does not do

• Key management — bring your own keys
• File or stream encryption — strings and bytes only
• Network protocols or TLS

Quickstart

[dependencies]
hefesto = "1.0.0"

use hefesto::HefestoError;

// Encrypt a field for DB storage (different output each call)
let ciphertext = hefesto::encrypt(
    "user@example.com",
    "tenant_secret_key",
    "master_server_key",
)?;

// Decrypt
let plaintext = hefesto::decrypt(
    &ciphertext,
    "tenant_secret_key",
    "master_server_key",
)?;
assert_eq!(plaintext, "user@example.com");

// Password hashing (one-way)
let hash = hefesto::hash_password("my_password")?;
assert!(hefesto::verify_password("my_password", &hash));

// Deterministic hash for DB lookups
// Same input + same key → always same output
let lookup = hefesto::hash_for_lookup("user@example.com", "tenant_secret_key");
// Store alongside the encrypted field, query with: WHERE email_lookup = ?

How it works

encrypt(value, tenant_key, master_key):

  salt_1  = OsRng (16 bytes)
  key_1   = Argon2id(tenant_key, salt_1)  →  32 bytes
  layer_1 = AES-256-GCM(value, key_1)     →  nonce_1 || ciphertext_1

  salt_2  = OsRng (16 bytes)
  key_2   = Argon2id(master_key, salt_2)  →  32 bytes
  layer_2 = AES-256-GCM(layer_1, key_2)  →  nonce_2 || ciphertext_2

  output  = Base64( salt_1 || salt_2 || layer_2 )

Both keys are required to decrypt. Compromising one key does not expose any data.

Security decisions

License

MIT