[SparkiDev]

Description

• fe_cswap/fe_cmov: put an optimization barrier on the mask so the compiler can't turn the swap into a branch (GCC -O3 on PPC64).
• 128-bit field mul/sq/sq2: apply the x19/x2 multiples to 64-bit limbs before the products, so every product is a plain signed 64x64->128 multiply. Removes multiplies whose operand is a limb's sign word, which have operand-dependent latency on Cortex-A55. Faster on x86_64 (9-17%). Now the default. NO_CURVED25519_128BIT_FOLDED keeps the original form.
• Cortex-A55/A53: WOLFSSL_CORTEX_A55/WOLFSSL_CORTEX_A53 turn on WOLFSSL_CURVE25519_FIXED_LATENCY_MUL. That forces the folded form and computes the 32-bit field's small multiples in unsigned arithmetic so Clang can't widen them into 64-bit multiplies. configure sets these when -mcpu/-mtune names cortex-a55 or cortex-a53.

Fixes zd#22787, zd#22796

Testing

Tested PPC64, Cortex-A55, x86_64.
./configure --enable-x25519 --enable-ed25519

[SparkiDev]

Code generated with PR:
https://github.com/wolfSSL/scripts/pull/713

[Copilot]

🟡 Changes recommended

The detection omits EXTRA_CFLAGS and EXTRA_CPPFLAGS, allowing Cortex-A55/A53 builds to select the 32-bit field implementation without enabling its timing mitigation.

1 open issue

• Include supplementary build flags in timing mitigation detection · New

What changed in this PR

This PR hardens wolfCrypt’s X25519/Ed25519 field operations against compiler-generated timing variations, while improving 128-bit arithmetic performance.

Changes:

• Add optimization barriers to conditional swaps and moves.
• Make folded 128-bit multiplication and squaring the default, with an opt-out.
• Add Cortex-A55/A53 detection and fixed-latency multiplication safeguards.

File	Description
wolfcrypt/​src/​fe_x25519_128.h	Add mask barriers and folded multiplication/squaring implementations.
wolfcrypt/​src/​fe_operations.c	Define hardening controls and protect 32-bit small-multiple arithmetic.
configure.ac	Detect Cortex-A55/A53 targets to enable timing mitigations.

_{Review effort: Balanced}

[github-actions]

MemBrowse Memory Report · Explore what changed →

zephyr-frdm_rw612

• FLASH: datas +16 B, log_const_area -8 B, rodata +20 B, text +10,016 B (+3.6%, 292,508 B / 67,108,864 B, total: 0% used)
• RAM: bss +49 B, datas +16 B (+0.1%, 58,423 B / 983,040 B, total: 6% used)

No memory changes detected for:

• gcc-arm-cortex-m0plus
• gcc-arm-cortex-m3
• gcc-arm-cortex-m4
• gcc-arm-cortex-m4-baremetal
• gcc-arm-cortex-m4-crypto-only
• gcc-arm-cortex-m4-dtls13
• gcc-arm-cortex-m4-min-ecc
• gcc-arm-cortex-m4-openssl-compat
• gcc-arm-cortex-m4-pkcs7
• gcc-arm-cortex-m4-pq
• gcc-arm-cortex-m4-rsa-only
• gcc-arm-cortex-m4-sp-math
• gcc-arm-cortex-m4-tls12
• gcc-arm-cortex-m4-tls13
• gcc-arm-cortex-m7
• gcc-arm-cortex-m7-pq
• gcc-arm-cortex-m7-tls13
• stm32-sim-stm32h753

---

_{Catch memory regressions in CI with MemBrowse. Free for open source.}