Claude
3bd81097e1
The header scan (Captain Bob, 2026-11-10): 788 source files -- 351 with the
SL-1.0 header, 12 with the old name (docs/working/experiments, kept by
ruling), 31 under someone else's licence (tools/kconfig, Linux's, GPL-2.0:
kept), and 394 with none. Ruled: the SPDX form; capsules (.4th, .f18) and
proofs (.thy) left for a ruling of their own (mkcapsule's 64x16 block format,
content-addressed capsules).
253 files now begin
SPDX-License-Identifier: LicenseRef-Starship-1.0
Copyright (c) 2023-2026 Robert A. James
as a /* */ block (C, headers, assembly, linker scripts) or # lines (scripts,
Makefiles, Kconfig; below a shebang or a coding line); tools/mkcapsule.c,
which had the copyright line, gets the SPDX line only.
Not touched: docs/working/ (archive and old campaign material, as the
ruling kept the experiments); v4/system/post_cases.c (generated by
v4/tools/mkpost.py, "do not edit" -- the generator has the header).
Comments only: the kernel builds on amd64, aarch64, riscv64; make -C v4
test-32: 39 programs, 0 failures; every changed script parses.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GE3SDvQn5EoxdGufk84zz2
41 lines
1.8 KiB
C
41 lines
1.8 KiB
C
/* SPDX-License-Identifier: LicenseRef-Starship-1.0
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* Copyright (c) 2023-2026 Robert A. James
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*/
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/* scalar25519.h -- arithmetic mod L (the Ed25519 base point's order),
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* for reducing SHA-512 output to a valid scalar and checking a
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* signature's S component for the RFC 8032 malleability requirement
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* (S < L, not just S < 2^256).
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*
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* Deliberately NOT the intricate hand-tuned "sc_reduce" reduction most
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* reference implementations use (a bespoke Barrett-style reduction with
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* constants specific to L, notoriously easy to transcribe wrong) --
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* this is a plain binary long-division reduction, one bit at a time.
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* O(512) steps per reduction; this is a verify-only, non-hot-path
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* library (one reduction per signature check), so the simpler,
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* more obviously-correct approach is the right tradeoff here.
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*/
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#ifndef SCALAR25519_H
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#define SCALAR25519_H
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#include <stdint.h>
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/* 32-byte little-endian scalars, reduced mod L where noted. */
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/* Reduce a 64-byte little-endian value (e.g. raw SHA-512 output) mod L,
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* producing a 32-byte little-endian result < L. */
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void scalar_reduce512(uint8_t out[32], const uint8_t in[64]);
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/* 1 if the 32-byte little-endian scalar is < L (a well-formed,
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* non-malleable signature component per RFC 8032), else 0. */
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int scalar_lt_L(const uint8_t s[32]);
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/* out = (a*b + c) mod L, all 32-byte little-endian scalars (a, b, c need
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* not already be reduced mod L, though every caller in this codebase
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* passes already-reduced inputs). Needed for EdDSA signing's
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* S = (k*a + r) mod L step -- verify never needed scalar multiplication,
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* only reduction, so this didn't exist until signing did. */
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void scalar_muladd(uint8_t out[32], const uint8_t a[32], const uint8_t b[32],
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const uint8_t c[32]);
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#endif /* SCALAR25519_H */
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