Skip to content

crypto.md

Latest commit

 

History

History
81 lines (54 loc) · 2.08 KB

crypto.md

File metadata and controls

81 lines (54 loc) · 2.08 KB
Raw

Cryptography

OpenKey is zero-knowledge toward the optional sync server: the server never receives the master password and never sees vault plaintext.

Key derivation

Password bytes for Argon2id:

utf8( trim(email).toLowerCase() + ":" + master_password )
Parameter Value
Algorithm Argon2id
Salt 16 random bytes (stored on the server, not secret)
Memory 65536 KiB
Iterations 3
Parallelism 4
Hash length 32
Output 32-byte master key

KDF parameters are stored as JSON on the account (algorithm, memory, iterations, parallelism, hashLength) so clients can evolve settings later. Default JSON matches the table above (algorithm: argon2id).

Auth hash

auth_hash = base64url_nopad( HMAC-SHA256(master_key, "openkey-auth") )

auth_hash is sent to the server for register / login. It is not the vault key. The master password is never sent.

Vault key

  • 32 random bytes generated on the client.
  • Wrapped with AES-256-GCM under the master key (encrypted_vault_key on the account).
  • All collection names and entry payloads are encrypted with the vault key.

Local DB encryption key (official app):

db_key = HMAC-SHA256(vault_key, "openkey-db")

AES-256-GCM wire format

Unpadded base64url of:

nonce (12 bytes) || ciphertext || tag (16 bytes)

Used for wrapped vault keys and for each encrypted field / payload blob.

Encoding

  • base64url, padding = stripped, matching the extension helper toB64Url.
  • Decoders accept padded or unpadded base64 / base64url.

Sealed boxes (orgs / shares)

Version byte 0x01. Unpadded base64url of:

0x01 || ephemeral_x25519_public (32) || nonce (12) || ciphertext || tag (16)

AES-GCM key:

SHA-256( utf8("openkey-seal-v1") || X25519_shared_secret )

Used so one user can wrap keys for another user’s X25519 public key without sharing the vault key in plaintext.

What never leaves the client

  • Master password
  • Master key
  • Vault key plaintext
  • Decrypted collection names and entry JSON