I recently came across the same issue with an old wallet.
Luckily they still have an old repo on github with a decrypt tool that you should be able to use to decrypt your wallet and get the private key.
The repo is here:
I'm not sure how versed you are with programming, but here's a quick summary of what I did to get it working and successfully sweep the funds into a separate wallet:
1: Firstly download the project, or if you have git you can simply clone it:
git clone https://github.com/Coinprism/backup-decrypt-tool.git
2: The tool is a .NET project written in C#. Tou will need to install .NET Core 2.0 Runtime in order to build the tool.
You can donload the install for windows here: https://dotnet.microsoft.com/download/dotnet/2.0/runtime
3: Once installed, open your terminal and navigate to the
Coinprism.BackupDecryptTool directory inside the project.
From here you can build and run the tool using the following command:
4: Provided it successfully builds, you will be prompted to enter your info:
- enter the the "priv" value from your backup as the "Encrypted value to decrypt"
- enter the "salt" value
- finally enter your password
5: The tool will decrypt your wallet and spit out the unencrypted private key and the corresponding bitcoin address.
Check that the address being displayed matches the one in your backup. If they are different, then check your info. Most likely your password is incorrect.
6: once you have the correct private key, you can sweep the funds using a bitcoin wallet.
I used Electrum wallet, as that runs locally and has a simple feature to sweep funds from a private key. You can put in any destination address as you wish while sweeping.