setup chacha circuit for NIVC folding

[lonerapier]

fixes ChaCha circuit for folding setup.

• add public step_in
• formatting

[lonerapier]

Couple of questions:

1. Can we move chacha inputs to bytes and then convert to 32 bits, just to be consistent with AES, but it will obviously add many constraints that can be saved by doing outside the circuit?
2. How does ChaCha handle plaintext padding? Do we need to compute ciphertext again when padded to 512/1024? In this case, isn't the ciphertext passed to circuit incorrect?

[0xJepsen]

2. How does ChaCha handle plaintext padding? Do we need to compute ciphertext again when padded to 512/1024? In this case, isn't the ciphertext passed to circuit incorrect?

since chacha is a stream cipher it technically doesn't need to do any padding. We could pad with zeros and then cut them after if we need maybe. You can decrypt symmetrically if you have all the same params since the encrypt and decrypt are just an XOR for the keystream. I Might need a little more context on the cipher text question you have here.

For the bytes to bits I added a helper the i referenced here with a test.
#58
When i tried to put it in the circuit i was breaking things so i think something might be wrong there just not sure what exactly.

[0xJepsen]

Nice work