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Tuck uses a random 256-bit data-encryption key (DEK) for the vault.

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Vault data

Titles, bodies, tag names, attachment bytes, and todo titles are encrypted with AES-256-GCM.

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Passphrase wrap

The vault passphrase is stretched with PBKDF2-HMAC-SHA256 using 600,000 iterations and a 16-byte salt, then used to wrap the DEK.

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Recovery wrap

The Recovery Kit independently wraps the same DEK so recovery does not require the normal passphrase.

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Client compatibility

The web and native Apple clients must use the same wrap format and snapshot shape. The iOS implementation intentionally follows the web vault contract instead of inventing a second crypto format.
Changes to the vault format are cross-platform compatibility changes. Treat them like a protocol migration, not a local implementation detail.