BIP halfagg TODOs

[jonasnick]

• Consider setting z_0 = 1 (actually this is the variant that is proposed in Chen & Zhao)
• Reconsider maximum number of signatures
• Add failing verification test vectors that exercise edge cases.
• Add aggregation test vectors (passing and failing, including edge cases)
• Test latest version of hacspec (run through checker)

[real-or-random]

• Should we allow the "empty" aggsig (n=0)? -- Yes.

[jonasnick]

Should we allow the "empty" aggsig (n=0)?

verify_aggregate currently returns true for an "empty" aggsig (s = 0). I think that makes sense.

[fjahr]

Can you elaborate on "Reconsider maximum number of signatures"? I assume this refers to this part in the BIP:

The maximum number of signatures that can be aggregated is 2<sub>16</sub> - 1. Having a maximum value is supposed to prevent integer overflows. This specific value was a conservative choice and may be raised in the future (TODO)

So would the goal of this would be to evaluate if it's feasible to raise this number now?