wolfCrypt SRAM PUF Support

[dgarske]

wolfCrypt SRAM PUF Support

Add SRAM PUF (Physically Unclonable Function) support to wolfCrypt. Derives device-unique cryptographic keys from the power-on state of SRAM memory using a BCH(127,64,t=10) fuzzy extractor with HKDF key derivation.

• wolfCrypt PUF API (wolfcrypt/src/puf.c, wolfssl/wolfcrypt/puf.h)
  • wc_PufInit, wc_PufReadSram, wc_PufEnroll, wc_PufReconstruct
  • wc_PufDeriveKey (HKDF-SHA256), wc_PufGetIdentity (SHA-256 device fingerprint)
  • wc_PufZeroize (secure context cleanup)
  • wc_PufSetTestData (synthetic SRAM for testing without hardware)
• BCH(127,64,t=10) error-correcting codec - corrects up to 10 bit flips per 127-bit codeword across 16 codewords
• WC_PUF_SHA3 build option - select SHA3-256 instead of SHA-256 for identity hash and HKDF (default: SHA-256)
• Precomputed GF(2^7) tables - const arrays in .rodata (no runtime init, thread-safe, flash-resident on embedded)
• ./configure --enable-puf (auto-enables HKDF dependency)
• CMake: WOLFSSL_PUF=yes
• WOLFSSL_USER_SETTINGS: define WOLFSSL_PUF and WOLFSSL_PUF_SRAM
• See wolfssl-examples/puf for example implementation on STM32 NUCLEO-H563ZI (Cortex-M33, STM32H563ZI)
• Supports test mode (synthetic SRAM)
• Builds to ~13KB .elf
• Tested on NUCLEO-H563ZI: enrollment, noisy reconstruction, key derivation all pass
• .github/workflows/puf.yml: host build + test workflow for PUF feature
• Doxygen API docs for all 8 public functions
• PUF group added to doxygen_groups.h

See example at: wolfSSL/wolfssl-examples#565

[dgarske]

Jenkins retest this please

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds SRAM PUF support to wolfCrypt, including a BCH(127,64,t=10) fuzzy extractor and HKDF-based key derivation, plus build-system integration, docs, and CI coverage.

Changes:

• Introduces new public PUF API (wc_Puf*) with context structure, enrollment/reconstruction, key derivation, identity, and zeroization.
• Adds BCH codec + PUF implementation and wires it into Autotools/CMake builds and new error codes/strings.
• Adds host-side test (synthetic SRAM mode), Doxygen grouping/docs, README blurb, and a GitHub Actions workflow.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
wolfssl/wolfcrypt/puf.h	New public header declaring the PUF API and constants/ctx layout.
wolfssl/wolfcrypt/include.am	Installs puf.h as a public header.
wolfssl/wolfcrypt/error-crypt.h	Adds PUF-specific error codes and updates span “last” markers.
wolfcrypt/src/error.c	Adds human-readable strings for new PUF error codes.
wolfcrypt/test/test.c	Adds puf_test() and invokes it from the main test runner when enabled.
wolfcrypt/src/puf.c	Implements SRAM PUF, BCH codec, identity hash, and HKDF key derivation.
src/include.am	Adds puf.c to lib sources when BUILD_PUF is enabled.
configure.ac	Adds --enable-puf and --enable-puf-test, enables HKDF automatically, defines build conditional.
cmake/functions.cmake	Adds PUF source inclusion when BUILD_PUF is set.
CMakeLists.txt	Adds WOLFSSL_PUF/WOLFSSL_PUF_TEST options and enables HKDF when PUF is on.
.wolfssl_known_macro_extras	Registers WC_PUF_SHA3 as a known macro.
doc/dox_comments/header_files/puf.h	Adds Doxygen API docs for PUF functions.
doc/dox_comments/header_files/doxygen_groups.h	Adds a Doxygen “PUF” group.
README.md	Mentions --enable-puf and links to the example.
.github/workflows/puf.yml	Adds CI job to configure/build/run wolfCrypt tests with PUF enabled.

Comments suppressed due to low confidence (2)

wolfcrypt/test/test.c:1

• As written, puf_test() returns success without running any assertions unless WOLFSSL_PUF_TEST && HAVE_HKDF && !NO_SHA256 are all set. However, the main test runner prints “PUF test passed!” whenever WOLFSSL_PUF is enabled, which can mask missing coverage in common build configurations (e.g., --enable-puf without --enable-puf-test). Consider compiling/registering puf_test() only when the full test dependencies are present, or returning a distinct “skipped” result that the harness prints as skipped instead of passed.
  wolfcrypt/test/test.c:1
• As written, puf_test() returns success without running any assertions unless WOLFSSL_PUF_TEST && HAVE_HKDF && !NO_SHA256 are all set. However, the main test runner prints “PUF test passed!” whenever WOLFSSL_PUF is enabled, which can mask missing coverage in common build configurations (e.g., --enable-puf without --enable-puf-test). Consider compiling/registering puf_test() only when the full test dependencies are present, or returning a distinct “skipped” result that the harness prints as skipped instead of passed.

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