Decrypting Zoom AppContext has an invalid IV/nonce

Zoom Apps
1

I’m following the instructions at https://marketplace.zoom.us/docs/zoom-apps/zoomappcontext/ and attempting to process the AppContext I’ve received from the appssdk using c# but I’ve run into an interesting problem.

I can decode/break up the base64 string into the iv, aad cipher and tag, but the iv is 82 bytes long. This is interesting as according to Authenticated Encryption in .NET with AES-GCM, a nonce should only be 12 bytes long and as best as I can figure out, the iv IS the nonce.

Am I missing something here. Is there an extra step I should be taking to convert an IV into a nonce?

2

It’s my understanding that the IV should be 12 bytes in size. I tested this out with the Basic Sample App and confirmed such.

I haven’t seen an instance where the IV is 82 bytes long - how are you checking the IV size?