How Vaultr Vault Encryption Works: Argon2id, AES-256-GCM and HKDF

Overview

Vaultr is a self-custody crypto super-app. Its vault uses a layered, client-side cryptographic pipeline so the server only ever stores ciphertext, never your passwords or plaintext secrets.

Every secret you store — across up to 16 vault slots, each with its own password — is protected by the same chain:

1. Key derivation (Argon2id): Your password is stretched into high-entropy key material.
2. Key expansion (HKDF-SHA256): That material is split into three purpose-specific sub-keys.
3. Authenticated encryption (AES-256-GCM): Your data is sealed and integrity-protected.

All of this happens on your device.

Quick answer

Vaultr derives a strong key from your slot password using Argon2id with OWASP-recommended parameters:

• 256 MB memory
• 4 iterations
• 2 parallelism

It then expands that key with HKDF-SHA256 into three sub-keys:

• Encryption key
• Authentication key
• Database key

Your data is sealed with AES-256-GCM using a 12-byte random nonce and a 16-byte authentication tag. All encryption and decryption run client-side, so the server only stores ciphertext.

1. Overall encryption pipeline

When you unlock a vault slot, Vaultr runs three stages locally on your device:

1. Key derivation (Argon2id)
   • Takes your slot password.
   • Produces high-entropy key material using a slow, memory-hard function.
2. Key expansion (HKDF-SHA256)
   • Takes the Argon2id output.
   • Derives three separate sub-keys: encryption, authentication, and database.
3. Authenticated encryption (AES-256-GCM)
   • Uses the derived keys to encrypt your data.
   • Produces ciphertext plus an authentication tag.

Because every stage runs client-side, Vaultr’s servers never see:

• Your slot passwords
• Your derived keys
• Your plaintext vault contents