fix: Improve get_second_key security by removing zero key return #1761

1. 
   crStiv commented at 0:44 am on February 11, 2025: none

   • Add empty list check with ValueError
   • Replace zero key return with InvalidContributionError for identical keys
   • Prevent potential cryptographic vulnerabilities from zero key usage
2. Update reference.py 99b30447b1
3. murchandamus added the label Proposed BIP modification on Feb 12, 2025
4. murchandamus added the label Pending acceptance on Feb 12, 2025
5. 
   murchandamus commented at 4:55 pm on February 12, 2025: contributor

   cc: @real-or-random, @jonasnick
6. 
   jonasnick commented at 5:40 pm on February 12, 2025: contributor

   Hi @crStiv,

   Returning the representation for the point at infinity is intentional. This is also what the BIPs pseudocode specifies. I see no reason to change this.

   Moreover, this PR would break the BIPs ability to identify disruptive signers (see section in the BIP). If the public keys are all the same and you abort, you do not know who generated the key honestly and who has just copied it.

7. 
   jonatack commented at 6:04 pm on February 13, 2025: member

   @crStiv Thank you for your proposal, but closing for now due to rejection by BIP author.
8. jonatack closed this on Feb 13, 2025

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Contributors
crStiv murchandamus jonasnick jonatack

Labels
Proposed BIP modification Pending acceptance