BIP374: add subtraction operator for GE class #1779

1. 
   VolodymyrBg commented at 3:19 pm on March 2, 2025: contributor

   This commit implements the subtraction operator (sub) for the GE (Group Element) class in the secp256k1.py file as requested in the TODO comment in reference.py.

   The implementation is straightforward, leveraging the existing neg method to define subtraction as addition with the negated element: self + (-a).

   After implementing the operator, the code in reference.py was simplified by replacing expressions like: s * G + (-e * A) with s * G - e * A

   This makes the code more readable and directly matches the mathematical notation used in the BIP-0374 specification.

2. jonatack added the label Proposed BIP modification on Mar 10, 2025
3. jonatack added the label Pending acceptance on Mar 10, 2025
4. 
   jonatack commented at 9:00 pm on March 10, 2025: member

   cc BIP authors @theStack @andrewtoth @RubenSomsen
5. 
   jonatack commented at 7:03 pm on April 14, 2025: member

   Note that the red CI here can be ignored; it is unrelated to this PR and is fixed on the master branch.
6. 
   jonatack commented at 7:04 pm on April 14, 2025: member

   Pinging BIP authors @theStack @andrewtoth @RubenSomsen for yay or nay on this change.
7. in bip-0374/reference.py:90 in 1434c8b49c outdated

   86@@ -87,11 +87,11 @@ def dleq_verify_proof(
   87     s = int.from_bytes(proof[32:], "big")
   88     if s >= GE.ORDER:
   89         return False
   90-    # TODO: implement subtraction operator (__sub__) for GE class to simplify these terms
   91-    R1 = s * G + (-e * A)
   92+    # Implemented subtraction operator (__sub__) for GE class to simplify these terms
   

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   theStack commented at 10:48 pm on April 14, 2025:

   After the TODO is implemented, this comment line doesn’t serve a purpose anymore and can just be removed (it sounds more like a commit message).

8. 
   theStack commented at 11:03 pm on April 14, 2025: contributor

   Concept ACK

   Even though it’s a tiny cosmetic change, it’s slightly more readable as it matches the formula in BIP directly. The subtraction operator implementation matches the one in secp256k1lab, a library which might be used in the future to unify all reference implementations in the BIPs repo that use the secp256k1 curve (it’s still unclear on how to exactly do this though).

   Nit: I think the two commits could just be squashed, with a descriptive commit message? Not sure how strict we are in the BIPs repo, but the new operator shouldn’t be used before it’s introduced, so if you plan to keep it divided into two commits, they should be swapped.

9. Implement subtraction operator for GE class in BIP-0374 reference code

   This commit implements the subtraction operator (sub) for the GE (Group Element) class in the secp256k1.py file as requested in the TODO comment in reference.py.
   
   The implementation is straightforward, leveraging the existing neg method to define subtraction as addition with the negated element: self + (-a).
   
   After implementing the operator, the code in reference.py was simplified by replacing expressions like:
   s * G + (-e * A) with s * G - e * A
   
   This makes the code more readable and directly matches the mathematical notation used in the BIP-0374 specification.
   
   Co-Authored-By: Sebastian Falbesoner <sebastian.falbesoner@gmail.com>

   7c80a699ff
10. VolodymyrBg force-pushed on Apr 15, 2025
11. 
    VolodymyrBg commented at 11:39 am on April 15, 2025: contributor

    Concept ACK

    Even though it’s a tiny cosmetic change, it’s slightly more readable as it matches the formula in BIP directly. The subtraction operator implementation matches the one in secp256k1lab, a library which might be used in the future to unify all reference implementations in the BIPs repo that use the secp256k1 curve (it’s still unclear on how to exactly do this though).

    Nit: I think the two commits could just be squashed, with a descriptive commit message? Not sure how strict we are in the BIPs repo, but the new operator shouldn’t be used before it’s introduced, so if you plan to keep it divided into two commits, they should be swapped.

    Done

12. VolodymyrBg requested review from theStack on Apr 15, 2025
13. jonatack renamed this:
    Implement subtraction operator for GE class in BIP-0374 reference code
    BIP374: add subtraction operator for GE class
    on Apr 15, 2025
14. andrewtoth approved
15. 
    andrewtoth commented at 1:45 pm on April 16, 2025: contributor

    ACK 7c80a699ffdb3dd5beb292e0b9324acd35c3a79f
16. 
    jonatack commented at 2:08 pm on April 16, 2025: member

    ACK
17. jonatack merged this on Apr 16, 2025
18. jonatack closed this on Apr 16, 2025

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Contributors
VolodymyrBg jonatack theStack andrewtoth

Review Requested
theStack

Labels
Proposed BIP modification Pending acceptance