In what context is the hash of a ed25519 public key used as an address?

Question

According to the docs, a Solana address is one of the following:

• an ed25519 public key
• a program-derived account address (32byte value forced off the ed25519 curve)
• a hash of an ed25519 public key with a 32 character string

The first 2 of these I've encountered numerous times, but I can't recall ever (knowingly) running into the third variation. Where is this used and what use case does supporting this type of address serve that user accounts and PDAs don't? I suppose they can be both on- and off-curve, but I don't really see any reason why you'd want that.

Answer 1

That last one is more of a legacy use-case. Before there was the concept of program-derived addresses, many of the native programs allowed you to use addresses that were strings hashed with the signing pubkey.

You'll see most of these instructions contain *_with_seed somewhere, like create_account_with_seed https://github.com/solana-labs/solana/blob/b3ea62fba31767fae75238a714081ab924cc6fbc/sdk/program/src/system_instruction.rs#L461

And these keys are created using Pubkey::create_with_seed https://github.com/solana-labs/solana/blob/b3ea62fba31767fae75238a714081ab924cc6fbc/sdk/program/src/pubkey.rs#L211

It would probably be better to deprecate these and use PDAs instead, but it's not too pressing an issue.