29 lines
668 B
Text
29 lines
668 B
Text
/* Zupt — Constant-Time MAC Comparison (Jasmin)
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* Copyright (c) 2026 Cristian Cezar Moisés
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* SPDX-License-Identifier: AGPL-3.0-or-later
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*
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* CT-REQUIRED: Timing independent of input byte values.
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* Compare 32 bytes as 4 × u64 — no byte-level access needed.
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*/
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export fn zupt_mac_verify_ct(
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reg u64 expected_ptr,
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reg u64 actual_ptr)
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-> reg u64
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{
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reg u64 diff a b tmp;
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inline int i;
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diff = 0;
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/* 4 × 8 bytes = 32 bytes. u64 loads — no size mismatch. */
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for i = 0 to 4 {
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a = [expected_ptr + 8 * i];
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b = [actual_ptr + 8 * i];
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tmp = a;
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tmp ^= b;
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diff |= tmp;
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}
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return diff;
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}
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