If you want to get knee-deep into the crypto:

WabiSabi paper on KVAC used for CoinJoins: https://eprint.iacr.org/2021/206.pdf

The Signal Private Group System and Anonymous Credentials Supporting Efficient Verifiable Encryption: https://eprint.iacr.org/2019/1416

We'll publish more resources on as we build out the protocol for Cashu.