Frequently Asked Questions

Is Arcanum part of the VeraCrypt project?

No. Arcanum is an independent project and is not affiliated with or endorsed by the VeraCrypt team. We use VeraCrypt’s open-source cryptographic library to ensure full container compatibility, but Arcanum is developed and maintained separately.

Is Arcanum compatible with desktop VeraCrypt?

Yes, completely. Arcanum containers are standard VeraCrypt containers. A vault created in Arcanum can be opened in VeraCrypt on Windows, macOS, or Linux, and a container created in desktop VeraCrypt can be opened in Arcanum. There is no proprietary format or metadata — the container header follows the VeraCrypt specification exactly.

What encryption algorithms are supported?

Arcanum supports all five VeraCrypt single ciphers — AES, Serpent, Twofish, Camellia, and Kuznyechik — plus ten cascade combinations (two or three ciphers in sequence). For key derivation: SHA-512, SHA-256, Whirlpool, Streebog, BLAKE2s-256, and Argon2id.

See How We Protect Your Data for the full list.

What happens if I forget my password?

Nothing can recover it. This is a fundamental property of the encryption, not a limitation of Arcanum. The container’s key material is derived from your password using thousands of PBKDF2 iterations and is never stored anywhere. Without the correct password (and keyfile, if you added one), the container is indistinguishable from random data.

There is no “forgot password” option and no backdoor. Keep a secure backup of your password.

Is the Pro version more secure than the free version?

No. All security features are identical across both versions. The Pro upgrade (available in the Play Store version) unlocks convenience features only — such as the ability to create more containers. The F-Droid version is fully free and has all features unlocked with no limitations.

Can I use Arcanum without the Play Store?

Yes. Arcanum is available on F-Droid. The F-Droid version has no Play Billing, no tracking, and all features enabled for free. It is the recommended version for privacy-conscious users.

What is a PIM and should I use it?

PIM (Personal Iterations Multiplier) adjusts the number of PBKDF2 iterations used to derive your key from your password. Leaving PIM empty uses VeraCrypt’s default of 500,000 iterations. Setting a PIM changes the count to 15,000 + (PIM × 1000) — so a PIM of 485 matches the default, a higher value (for example 700 → 715,000 iterations) strengthens key derivation at the cost of slower unlock, and a lower value weakens it. Because a PIM below 485 falls under the default, the wizard then requires a password of at least 20 characters. With Argon2id the PIM sets memory rather than iterations and that floor is 12.

For most users, leaving PIM empty is the right choice. Whatever you pick, a strong password matters far more than the PIM. For guidance while creating a vault, see Choosing a PIM.

What is a keyfile?

A keyfile is any file you designate as an additional authentication factor. To open a container protected by a keyfile, you need both the password and the exact keyfile. Arcanum can generate one for you, filled with cryptographically secure random data, or you can point it at an existing file such as a photo or a document — though a file some app might rewrite is a poor choice, since one changed byte makes it useless. Keep the keyfile safe — losing it is equivalent to losing your password. See Keyfiles for generating, sizing, and storing them.

Why does the app look like a calculator?

This is the calculator disguise feature. See Calculator Disguise for how it works and how to access the vault interface.

Can I shrink a vault?

No. Shrinking a container is fundamentally impossible without first mounting it, and neither Arcanum nor desktop VeraCrypt supports it.

The reason is how VeraCrypt encryption works: the entire container — including filesystem metadata — is encrypted as a flat array of bytes. From the outside, Arcanum cannot tell which sectors are occupied by real files and which are free space. It only sees ciphertext.

Growing a container avoids this problem, which is why desktop VeraCrypt offers it: new space is appended to the end of the file and existing data stays at exactly the same byte offsets, so nothing has to move. Arcanum does not offer it, because the filesystem inside the container would stay its original size and the added space would be unusable — see Running Out of Space.

Shrinking is a different matter entirely. To do it safely you would need to:

1. Decrypt the container and mount the filesystem.
2. Read the filesystem structure to determine where real data ends.
3. Relocate the filesystem so it fits within the smaller boundary.
4. Truncate the container file.

This is equivalent to running resize2fs — and it requires a separate implementation for every supported filesystem (FAT32, exFAT, ext4, and any future additions). Desktop VeraCrypt does not support this either.

Practical alternative: create a new, smaller vault and move your files into it. Both vaults can be open at the same time, so the files go straight across without passing through your phone’s storage.

Can I move files from one vault into another?

Yes, and without the files touching your phone’s storage on the way. Mount both vaults - Arcanum keeps as many open as you mount - then select what you want in one of them, tap Move or Copy, and pick the other vault from the list the sheet opens on. Arcanum reads out of one vault and writes into the other with both mounted in the same app, so the readable bytes exist only in its memory.

The list of vaults only appears when more than one is mounted; with a single vault open the sheet goes straight to its folders. See Working with Files in a Vault.

Why does my vault close when I switch to another app?

Because Android closed Arcanum. A mounted vault exists only inside the running app - the keys and the open file live in its memory - so when Android reclaims that memory, which it does to whichever backgrounded app it likes, the vault closes with it. Nothing is lost or damaged; the vault is simply locked again, and an import or a file you had open in another app stops where it was.

Settings - Security - Keep vaults open in the background is the answer to this. With it on, Arcanum holds itself in memory for as long as a vault is open, which moves it out of the group Android takes from first. It is off by default.

Two things it does not do. It is not a promise: a phone genuinely short of memory, and some manufacturers’ own battery savers, will still close the app. And it does not touch auto-lock - the app still locks on its own schedule, and a vault set to close when you leave the app or when the screen goes off still does. It only stops Android from closing what you did not ask to close.

If the calculator disguise matters to you, read what it shows in the notification shade before turning it on.

Can I download files straight into a vault?

Yes. Turn on External app access for the vault, open it, and pick its folder when the other app asks where to save. What that app writes is encrypted on the way in, and nothing is decrypted to your phone’s storage along the way. Turn on Settings - Security - Keep vaults open in the background as well, so Android does not close the vault while you are in the other app.

The one thing to keep in mind is what the other app does outside the vault: some write to their own temporary folder first, and readers cache thumbnails and pages in their own storage. See Other Apps and a Vault.

Does Arcanum work on Android 10 and later?

Arcanum requires Android 10 (API 29) or later.