Core concepts

Your vault is your encrypted drive: the entire tree of folders and files that belong to you. It is presented like any normal drive, but every name and every byte inside it is encrypted on your device before it is stored. The server holds only ciphertext and the structure needed to fetch it back.

Your passphrase is the one secret that unlocks the vault. It is not a login credential: your account password handles signing in. Instead, zcrypt feeds the passphrase through a key derivation function in your browser to produce your vault key. That key, and the passphrase behind it, are never transmitted to our servers.

Folders are real and nestable, just like on a desktop drive. Open one and create another inside it, as deep as you like. A folder's name is encrypted on your device exactly like file contents, so your organization is private too. When the vault is locked, names show as placeholders until you unlock.

A folder can also have its own password layered on top. See Per-folder encryption.

zcrypt uses envelope encryption. Each file gets its own random content encryption key (CEK) that encrypts that file's bytes with AES-256-GCM. The CEK itself is then encrypted (“wrapped”) by the key derived from your passphrase.

The payoff: your passphrase only ever has to protect small wrapped keys, not gigabytes of data. To open a file, zcrypt unwraps its CEK with your vault key, then uses the CEK to decrypt the content, all locally.

Each file is split into chunks first: pieces sized to your device (4, 8, 10 or 16 MiB; 10 MiB is the usual). Each chunk is then compressed and encrypted on its own. Chunks are what actually get uploaded, one per request, to the repositories or channel on your connected platform. On download, zcrypt fetches the chunks, verifies them, and reassembles the file on your device.

The vault has a single lock state, surfaced as one pill in the interface and unlocked through one modal. Enter your passphrase once and the whole vault unlocks for the rest of the session. There is no per-file or per-folder prompting to wade through.

The unlock lasts for a session time-to-live (TTL). When it expires, the pill returns to locked and the next action that needs your key reopens the single modal.

When unlocking, you can choose “keep me unlocked on this device.” Instead of re-typing your passphrase every session, zcrypt stores it encrypted at rest in your browser's IndexedDB, sealed under a non-extractable key the browser will not hand back to any script.