[crypto] Harden RSA key import CRT checks with random mask #226
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mkannwischer wants to merge 2 commits intomasterfrom
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[crypto] Harden RSA key import CRT checks with random mask #226mkannwischer wants to merge 2 commits intomasterfrom
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Multiply a nonzero random mask into the d_p, d_q, and i_q validity checks. Instead of computing e * d_p mod (p-1) and comparing to 1, we now computes r * e * d_p mod (p-1) and the C side compares against r. This avoids the multi-limb value 1 as an intermediate or comparison target, hardening the check against fault injection. Signed-off-by: Matthias J. Kannwischer <matthias@zerorisc.com>
The existing tests only checked rejection of an invalid d_p. Add test cases for invalid d_q and i_q as well, each constructed by flipping an arbitrary single bit in the valid test vector. Signed-off-by: Matthias J. Kannwischer <matthias@zerorisc.com>
mkannwischer
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Mar 25, 2026
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| bn.wsrr w20, URND | ||
| bn.rshi w20, w31, w20 >> 1 | ||
| bn.addi w20, w20, 1 |
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Is a 256-bit (or rather-255 bit) random mask sufficient here, or do we need a full-width masks?
If we need a full width masks, then we would need different masks mod p, mod q, and mod p-1.
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As proposed in #170, this PR
multiplies a nonzero random mask into the d_p, d_q, and i_q
validity checks. Instead of computing e * d_p mod (p-1) and
comparing to 1, we now computes r * e * d_p mod (p-1) and
the C side compares against r.
This avoids the multi-limb value 1 as an intermediate or
comparison target, hardening the check against fault injection.
I have also added additional negative tests that test these failures cases for invalid d_q and i_q.