When I learned crypto 5-10 years ago, it turned out that a lot of "building blocks" are mostly hacks. Looking back from 2020s we see that some of the standards that we use for the last 20-30 years can in principle be thrown out of the window (they can't for compatibility reasons, though) and replaced with much cleaner and more universal replacements.

If we do not talk about modern exotic stuff (post-quantum crypto, zkSNARKS, homomorphic encryption), the 99% of everyday cryptography is based on two building blocks:

1. Symmetric crypto for ciphers and hash functions.

2. Algebraic group with "hard discrete log problem" for key exchange, signatures, asymmetric encryption and simple zero-knowledge proofs.

Historically, these two categories are filled with a zoo of protocols. E.g. AES is a block cipher, but SHA(1,2) is a hash function.

Today, you can roughly achieve everything of the above with two universal building blocks:

- Keccak for all of symmetric crypto: it is suited both for encryption, hashing, duplex transcripts for ZK protocols etc.

- Ristretto255 group based on Curve 25519: for diffie-hellman, signatures, key derivation, threshold schemes, encryption and more.

The problem is that none of the described features is implemented in a turnkey standard, and we are still stuck using older crypto. Heck, even Git is using SHA-1 still.

Then, after you have your building blocks, there are more hairy stuff such as application-specific protocols: TLS, Signal, PAKE/OPAQUE, proprietary hardware security schemes for full disk encryption and access controls etc.