# Decrypting Zoom AppContext has an invalid IV/nonce **URL:** \ **Category:** Zoom Apps\ **Created:** [December 16, 2022, 7:33pm UTC](https://devforum.zoom.us/t/decrypting-zoom-appcontext-has-an-invalid-iv-nonce/80408 "2022-12-16T19:33:38Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![grover](https://sea2.discourse-cdn.com/flex016/user_avatar/devforum.zoom.us/grover/32/32774_2.png) [@grover](https://devforum.zoom.us/u/grover)\ **Post date:** [December 16, 2022, 7:33pm UTC](https://devforum.zoom.us/t/decrypting-zoom-appcontext-has-an-invalid-iv-nonce/80408/1 "2022-12-16T19:33:38Z")
I’m following the instructions at [https://marketplace.zoom.us/docs/zoom-apps/zoomappcontext/](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](https://www.scottbrady91.com/c-sharp/aes-gcm-dotnet), 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? ---
**Author:** ![MaxM](https://sea2.discourse-cdn.com/flex016/user_avatar/devforum.zoom.us/maxm/32/42303_2.png) [@MaxM](https://devforum.zoom.us/u/MaxM)\ **Post date:** [December 19, 2022, 9:21pm UTC](https://devforum.zoom.us/t/decrypting-zoom-appcontext-has-an-invalid-iv-nonce/80408/2 "2022-12-19T21:21:17Z")
It’s my understanding that the IV should be 12 bytes in size. I tested this out with the [Basic Sample App](https://github.com/zoom/zoomapps-sample-js) and confirmed such. I haven’t seen an instance where the IV is 82 bytes long - how are you checking the IV size?