fix: splitting scalars edge case#20686
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notnotraju wants to merge 5 commits intomerge-train/barretenbergfrom
Open
fix: splitting scalars edge case#20686notnotraju wants to merge 5 commits intomerge-train/barretenbergfrom
notnotraju wants to merge 5 commits intomerge-train/barretenbergfrom
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…alar multiplication Tests for the negative-k2 bug in split_into_endomorphism_scalars (Fr and Fq), plus EC-level scalar multiplication tests (g1 and grumpkin) showing the bug produces wrong points. Includes endomorphism_scalars.py for deriving the boundary scalars. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
…and changed the tests to be regression tests accordingly.
notnotraju
added
bberg-int-audit
…ztec-packages into rk/splitting-scalars-edge-case
notnotraju
commented
Feb 19, 2026
| // When negative, t1 = k2 + r is 254 bits (upper limbs nonzero). | ||
| // Fix: decrement c1 by 1, equivalent to adding |b1| to k2. | ||
| // This shifts k2 by +|b1| (~127 bits, now positive) and k1 by -a1 (~64 bits), | ||
| // keeping both within 128 bits. See endomorphism_scalars.py for more details. |
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this is the main content change.
notnotraju
commented
Feb 20, 2026
| * | ||
| * See ecc/fields/endomorphism_scalars.py for an analysis. | ||
| */ | ||
| static void test_endomorphism_negative_k2_regression() |
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regression test that shows that this splitting scalars thing affected goblin
…d secpk1 (to at least generate parameters)
notnotraju
commented
Feb 23, 2026
| # Computes (k1, k2) with k ≡ k1 - λ·k2 (mod r) and |k1|, |k2| < 2^128. | ||
| # See §0 for the derivation (Babai's nearest plane). | ||
| # | ||
| # SUBTLETY — k2 CAN BE NEGATIVE: |
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this was the issue that we needed to fix.
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Fixes an edge case in the
split_into_endomorphism_scalarsmethod. Adds detailed documentation for the algorithm in the form of a literate python program and regression tests for EC edge cases andbiggroup_goblin.