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[pentest] Ensure KMAC reset #31083

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[pentest] Ensure KMAC reset #31083

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6 changes: 4 additions & 2 deletions sw/device/tests/penetrationtests/firmware/sca/sha3_sca.c
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Original file line number Diff line number Diff line change
Expand Up @@ -527,8 +527,6 @@ status_t handle_sha3_sca_batch(ujson_t *uj) {
}

for (uint32_t i = 0; i < uj_data.num_enc; ++i) {
kmac_reset();

Comment on lines 529 to -531

@ziuziakowska ziuziakowska Aug 21, 2026

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I'm not very familiar, but should there not be a kmac_reset at the start outside the loop? Otherwise it looks like the KMAC state is inconsistent before the first iteration, rather than after the last, which seems like it just moves the issue.

@luismarques luismarques Aug 21, 2026 •
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A reset after the absorb was the most prevalent approach (see kmac_sca.c), this one was the outlier, so moving this reset to after the absorb seemed like the obvious choice. I was assuming that this would preserve the necessary invariants, with all previous commands and state changes leaving it reset/idle (so this would be a systematic approach), but I'm happy to be corrected if that's not the case.

@nasahlpa @siemen11 will know best, so I defer to them to specify what the approach should be.

if (sha3_serial_absorb(sha3_batch_messages[i], kMessageLength) !=
sha3ScaOk) {
return ABORTED();
Expand All @@ -545,6 +543,10 @@ status_t handle_sha3_sca_batch(ujson_t *uj) {
for (uint32_t j = 0; j < kDigestLength; ++j) {
batch_digest[j] ^= out[j];
}

// Reset before the next absorb since KMAC must be idle before starting
// another absorb.
kmac_reset();
}

// Acknowledge the batch command. This is crucial to be in sync with the host
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