Default Address

[realnimish]

Zero address has a known private key in the sr25519/ed25519 schema. So for our default_address state variable in azns_registry we need to determine what address to use with a sufficient guarantee that no one can access it.

Substrate should provide a network-wide burn-address which ensures developers can refer to that address when they want to burn something. Right now, either we can choose a random address and hope no one finds its public key or add a check for every mutable message to ensure the caller is not the default_address.

More details: use-ink/ink#1255

[realnimish]

Following ideas were discussed with the team and Hernando Castano (the PR author):

1. Use random address and hope no one finds it.

2. Add an additional check in our contract disallowing caller with the given address.

3. Use option instead.

4. Substrate should provide a null/burn address which guarantees that the signer cannot have the said address.

And we've decided to go with approach (3) because of its idiomatic nature and security guarantee.