How to Fix Encrypted Saves That Stop Decrypting After a Key or IV Change

Change the key, IV, or mode and every existing encrypted save becomes garbage. Store the IV with the file and tag the crypto version so old saves remain decryptable.

How to fix it

1. Store the IV with the file

A unique IV per save must be written alongside the ciphertext, not hardcoded. Reuse or loss of the IV makes decryption fail or weakens security.

2. Version the encryption scheme

Prefix the file with a crypto-version byte. When you change cipher or key derivation, branch on this byte so old files use the old scheme.

3. Keep old keys for migration

When rotating keys, retain the previous key long enough to decrypt-and-re-encrypt existing saves, or saves made before the rotation are lost forever.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.