I have been working on an assignment to solve argon2i hashes but unfortunately. I am not able to use GPU with JTR i.e. no opencl mode for argon2. Thus the speed is very slow. Any suggestion how to proceed using GPU based attack?
I am not able to use GPU with JTR i.e. no opencl mode for argon2. Thus the speed is very slow. Any suggestion how to proceed using GPU based attack?
This is exactly one of the reasons that argon2 exists.
It was explicitly designed so that hardware other than a general purpose CPU provides only a minimal advantage, if any.
Proceeding with GPU based attacks is probably a waste of a GPU. One of the core features of argon2 is a large amount of memory usage, which GPUs are not exceptionally good at.
Your best bet is to have a large number of normal computers with sufficient RAM, or investigate FPGAs. FPGAs may not be able to provide a worthwhile advantage due to the memory requirement, and they will not be so easy to work with (unless you are already skilled with an HDL).
Neither option will be cheap, and I assume that they are not practical in your situation.
Most likely, you are stuck testing one password guess at a time using your CPU. In such a case, the best that you can do is to use a good word list and hope that the password is weak. Either that, or find some alternative method of finding the password that doesn't involve cracking argon2 hashes.