Regenerate SP sources: constant-time sp_*_from_mp#10898
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Pull request overview
This PR regenerates the single-precision (“sp”) implementation sources to make sp_<N>_from_mp() convert secret mp_int inputs in constant time by iterating a fixed amount (bounded by output size) and masking digits at/after a->used.
Changes:
- Regenerated multiple
sp_*_from_mp()implementations to avoid looping based ona->used(magnitude-dependent timing). - Added branchless masking logic to zero out digits beyond
a->usedduring conversion. - Applied the same pattern across several architecture-specific and generic SP backends.
Reviewed changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.
Show a summary per file
| File | Description |
|---|---|
| wolfcrypt/src/sp_x86_64.c | Regenerated constant-time masking conversion for sp_*_from_mp() in SP x86_64 backend. |
| wolfcrypt/src/sp_cortexm.c | Regenerated constant-time masking conversion for sp_*_from_mp() in Cortex-M backend. |
| wolfcrypt/src/sp_c64.c | Regenerated constant-time masking conversion for sp_*_from_mp() in 64-bit C backend. |
| wolfcrypt/src/sp_c32.c | Regenerated constant-time masking conversion for sp_*_from_mp() in 32-bit C backend. |
| wolfcrypt/src/sp_armthumb.c | Regenerated constant-time masking conversion for sp_*_from_mp() in ARM Thumb backend. |
| wolfcrypt/src/sp_arm64.c | Regenerated constant-time masking conversion for sp_*_from_mp() in ARM64 backend. |
| wolfcrypt/src/sp_arm32.c | Regenerated constant-time masking conversion for sp_*_from_mp() in ARM32 backend. |
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Regenerated with the updated generator so sp_<N>_from_mp() clamps the read index to a valid digit (0 when a->used == 0), avoiding an out-of-bounds or NULL digit read in the fixed-count constant-time loop while keeping the conversion constant time. Addresses the Copilot review comments on this PR (wolfSSL#10898) and on wolfSSL/scripts#626. Verified (--enable-sp, gcc 15.2): ec_p521_kex diff 0, ec_p521_sign diff 55; make check passes. Generated by wolfSSL/scripts#626
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Jenkins retest this please |
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Fenrir Automated Review — PR #10898
Scan targets checked: wolfcrypt-bugs, wolfcrypt-src
No new issues found in the changed files. ✅
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Regenerated the single-precision C sources so that sp_<N>_from_mp() converts secret inputs (ECDH/ECDSA private keys and nonces) in constant time: a fixed-count loop bounded by the output size with masked reads at/after a->used, instead of looping a->used times (which leaked the value's magnitude through the executed-instruction count). Fixes the ct-callgrind constant-time failures for P-521 (ec_p521_kex, ec_p521_sign) and hardens the same pattern across all curves and key sizes (108 sp_*_from_mp functions in sp_c32/sp_c64, sp_arm32/sp_arm64/sp_armthumb/ sp_cortexm and sp_x86_64). Verified (--enable-sp, gcc 15.2): ec_p521_kex diff 156 -> 0, ec_p521_sign diff 367 -> 55 (tol 300); testwolfcrypt RSA/ECC KATs pass. Generated by wolfSSL/scripts#626
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Description
Regenerated the single-precision C sources so that sp__from_mp() converts secret inputs (ECDH/ECDSA private keys and nonces) in constant time: a fixed-count loop bounded by the output size with masked reads at/after a->used, instead of looping a->used times (which leaked the value's magnitude through the executed-instruction count).
Testing
Fixes the ct-callgrind constant-time failures for P-521 (ec_p521_kex, ec_p521_sign) and hardens the same pattern across all curves and key sizes (108 sp_*_from_mp functions in sp_c32/sp_c64, sp_arm32/sp_arm64/sp_armthumb/ sp_cortexm and sp_x86_64).
Verified (--enable-sp, gcc 15.2): ec_p521_kex diff 156 -> 0, ec_p521_sign diff 367 -> 55 (tol 300); testwolfcrypt RSA/ECC KATs pass.
Generated by https://github.com/wolfSSL/scripts/pull/626