Question 1

How does the encryption work?

Accepted Answer

Your password is stretched into a 256-bit key using PBKDF2 with 250,000 iterations and a random salt, then used to encrypt your data with AES-256 in GCM mode. GCM also authenticates the data, so any tampering or a wrong password is detected and decryption simply fails rather than returning garbage. All of this happens in your browser using the Web Crypto API — the same cryptographic engine browsers use for HTTPS. The encrypted output bundles the salt and a random initialisation vector with the ciphertext so the recipient needs only the file and the password.

Question 2

Is anything uploaded to your servers?

Accepted Answer

No. The file, the text, the password, and the resulting key never leave your device — there is no upload step in this tool. You can verify it by disconnecting from the internet: encryption and decryption keep working. Because we never receive your data or your password, we have zero knowledge of what you encrypt; even we could not decrypt it. The encrypted file you download is yours to share through any channel you trust.

Question 3

How do I share an encrypted file safely?

Accepted Answer

Encrypt the file here, then send the resulting .ttbx file to your recipient through any channel — email, chat, a USB stick. Crucially, send the password through a different channel than the file (for example, the file by email and the password by a phone call or signal message). That way, intercepting one without the other is useless. The recipient opens it on this page’s Decrypt tab with the password. A hosted, self-destructing share link that does this for you is coming with Pro.

Question 4

What makes a good encryption password?

Accepted Answer

The security of the file rests entirely on the password, so make it long and unpredictable — a passphrase of several random words, or a 16+ character random string. Avoid anything guessable or reused from another account, because an attacker who has the encrypted file can try passwords offline. Our password generator can create a strong one, and our checker can rate it. If you lose the password there is no recovery: zero-knowledge means we cannot reset it for you.

Question 5

Can I encrypt large files?

Accepted Answer

Yes, within the limits of your device’s memory, since the file is processed in your browser. Very large files (multiple gigabytes) may be slow or hit browser memory limits because the whole file is held in memory during encryption. For everyday documents, photos, archives, and media this works smoothly. If you routinely need to store or send large encrypted files, the upcoming Pro encrypted storage and hosted links are designed for that.

Encrypt Files & Text — Free, AES-256, Zero-Knowledge

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