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[SECP256K1] WNAF of lambda_split output has max size 129
Summary: Partial backport 9/11 of secp256k1 [[bitcoin-core/secp256k1#830 | PR830]]: bitcoin-core/secp256k1@2edc514 Depends on D8044. Test Plan: ninja check-secp256k1 Reviewers: #bitcoin_abc, deadalnix Reviewed By: #bitcoin_abc, deadalnix Differential Revision: https://reviews.bitcoinabc.org/D8045
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src/ecmult_impl.h

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -428,8 +428,8 @@ static int secp256k1_ecmult_wnaf(int *wnaf, int len, const secp256k1_scalar *a,
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struct secp256k1_strauss_point_state {
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secp256k1_scalar na_1, na_lam;
431-
int wnaf_na_1[130];
432-
int wnaf_na_lam[130];
431+
int wnaf_na_1[129];
432+
int wnaf_na_lam[129];
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int bits_na_1;
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int bits_na_lam;
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size_t input_pos;
@@ -466,10 +466,10 @@ static void secp256k1_ecmult_strauss_wnaf(const secp256k1_ecmult_context *ctx, c
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secp256k1_scalar_split_lambda(&state->ps[no].na_1, &state->ps[no].na_lam, &na[np]);
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/* build wnaf representation for na_1 and na_lam. */
469-
state->ps[no].bits_na_1 = secp256k1_ecmult_wnaf(state->ps[no].wnaf_na_1, 130, &state->ps[no].na_1, WINDOW_A);
470-
state->ps[no].bits_na_lam = secp256k1_ecmult_wnaf(state->ps[no].wnaf_na_lam, 130, &state->ps[no].na_lam, WINDOW_A);
471-
VERIFY_CHECK(state->ps[no].bits_na_1 <= 130);
472-
VERIFY_CHECK(state->ps[no].bits_na_lam <= 130);
469+
state->ps[no].bits_na_1 = secp256k1_ecmult_wnaf(state->ps[no].wnaf_na_1, 129, &state->ps[no].na_1, WINDOW_A);
470+
state->ps[no].bits_na_lam = secp256k1_ecmult_wnaf(state->ps[no].wnaf_na_lam, 129, &state->ps[no].na_lam, WINDOW_A);
471+
VERIFY_CHECK(state->ps[no].bits_na_1 <= 129);
472+
VERIFY_CHECK(state->ps[no].bits_na_lam <= 129);
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if (state->ps[no].bits_na_1 > bits) {
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bits = state->ps[no].bits_na_1;
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}

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