[HOW TO OPEN A .CRYPT FILE]

1. Copy the backup into Android/media/com.whatsapp/WhatsApp/Databases/ on the phone (older Android versions: WhatsApp/Databases/), named msgstore.db.crypt14 (or 15).
2. Install WhatsApp and verify the same phone number the backup was made with.
3. Tap Restore when WhatsApp offers it. For an end-to-end encrypted backup it will ask for your backup password or 64-digit key.

This is the only method that needs no technical steps, and the only one that works without the key file.

• crypt12 and crypt14: the key is a small file at /data/data/com.whatsapp/files/key on the phone that made the backup. Android only lets WhatsApp read it, so getting it requires a rooted phone. WhatsApp also holds it on its servers, tied to your number, which is how a normal restore works.
• crypt15 (end-to-end encrypted backups): the key is the 64-digit key you were shown when you turned on encrypted backups, or it is unlocked by the password you chose. If both are lost, nobody — including WhatsApp — can open the backup.

If you have the key, the open-source wa-crypt-tools decrypts crypt12, crypt14 and crypt15 backups into an ordinary SQLite database that any SQLite browser opens. It runs on your own computer, so the backup and the key stay with you.

Only do this with your own backups. Reading someone else's chat history without permission is illegal in most countries.

A site that offers to decrypt a .crypt file you upload — without asking for the key — cannot do what it claims: the key is not in the file. At best it fails; at worst it keeps a copy of your entire chat history, or asks for payment and delivers nothing.

If a .crypt file appeared next to your own documents with a ransom note, it is not a WhatsApp backup: see how to decrypt encrypted files for what to do about ransomware.