Lean Crypto Library

The leancrypto library is a cryptographic library that exclusively contains only PQC-resistant cryptographic algorithms. The algorithm implementations have the following properties:

• minimal dependencies: only minimal POSIX environment needed - function calls are abstracted into helper code that may need to be replaced for other environments (see the Linux kernel support in linux_kernel for replacing the POSIX calls)

• extractable: the algorithms can be extracted and compiled as part of a separate project,

• flexible: you can disable algorithms on an as-needed basis using meson configure,

• fully thread-safe when using different cipher contexts for an invocation: there is no global state maintained for the algorithms,

• stack-only support: all algorithms can be allocated on stack if needed. In addition, allocation functions for a usage on heap is also supported,

• size: minimizing footprint when statically linking by supporting dead-code stripping,

• performance: provide optimized code invoked with minimal overhead, thus significantly faster than other libraries like OpenSSL, and

• testable: all algorithm implementations are directly accessible via their data structures at runtime.

Status

Type	Service	Status
Linux User Space	GitHub
Linux Kernel Space	GitHub
macOS User Space	GitHub
Small Stack	GitHub
ASAN Address Check	GitHub
CodeQL Scan	GitHub
Codacy Scan	GitHub
Windows User Space	GitHub

Library Build

If you want to build the leancrypto shared library, use the provided Meson build system:

1. Setup: meson setup build

2. Compile: meson compile -C build

3. Test: meson test -C build

4. Install: meson install -C build

Library Build for Linux Kernel

The leancrypto library can also be built as an independent Linux kernel module. This kernel module offers the same APIs and functions as the user space version of the library. This implies that a developer wanting to develop kernel and user space users of cryptographic mechanisms do not need to adjust to a new API.

Note: The user space and kernel space versions of leancrypto are fully independent of each other. Neither requires the presence of the other for full operation.

To build the leancrypto Linux kernel module, use the Makefile in the directory linux_kernel:

1. cd linux_kernel

2. make

3. the leancrypto library is provided with leancrypto.ko

Note, the compiled test kernel modules are only provided for regression testing and are not required for production use. Insert the kernel modules and check dmesg for the results. Unload the kernel modules afterwards.

The API specified by the header files installed as part of the meson install -C build command for the user space library is applicable to the kernel module as well. When compiling kernel code, the flag -DLINUX_KERNEL needs to be set.

For more details, see linux_kernel/README.md.

Library Build for Windows

The leancrypto library can be built on Windows using MSYS2. Once MSYS2 is installed along with meson and the mingw compiler, the standard compilation procedure outlined above for meson can be used.

The support for full assembler acceleration is enabled.

Library Build for Other Environments

If you need leancrypto to work in other environments like small embedded systems, you need:

1. Adjust the build system as needed to compile and link it

2. Adjust the file ext_headers.h to point to the right header files and locations.

3. set the flag LC_MEM_ON_HEAP if your environment only has a limited stack size. When set, functions with large memory requirements use the heap instead of the stack for this memory. The maximum stack size used by a function is 2048 bytes and is verified by a compiler check.

An example on the approach is given with the Linux kernel support found in the directory linux_kernel.

Cryptographic Algorithms

Leancrypto offers various cryptographic algorithms:

• Authenticated Encryption with Associated Data

  • Ascon 128 AEAD and Ascon 128a AEAD

  • Ascon Keccak 256/256, 256/512 and 512/512 AEAD, full specification provided with aead/doc/Ascon-Keccak.pdf

  • cSHAKE-based AEAD algorithm - algorithm devised with leancrypto, see cshake_crypt.c for full specification

  • hash-based AEAD algorithm - algorithm devised with leancrypto, see hash_crypt.c for full specification

  • KMAC-based AEAD algorithm - algorithm devised with leancrypto, see kmac_crypt.c for full specification

  • AES-based AEAD algorithm using SHA2 - see symhmac_crypt.c for full specification

  • AES-based AEAD algorithm using Keccak-based KMAC - see symkmac_crypt.c for full specification

• Pseudo Random Number Generators

  • XDRBG256 - see drng/doc/ToSC2024_1_01.pdf for full specification and proof

  • cSHAKE-based PRNG - see cshake_drng.c for full specification - it complies with the XDRBG specification given in drng/doc/ToSC2024_1_01.pdf

  • KMAC-based PRNG - see kmac_drng.c for full specification - it complies with the XDRBG specification given in drng/doc/ToSC2024_1_01.pdf

  • SHAKE-based PRNG

  • SP800-90A Hash and HMAC DRBG

  • ChaCha20-based PRNG - see https://www.chronox.de/lrng for specification

• Message Digest algorithms

  • SHA2-256, SHA2-512

  • SHA3-224, SHA3-256, SHA3-384, SHA3-512

  • SHAKE-128, SHAKE-256

  • cSHAKE-128, cSHAKE-256

  • Ascon 128 / 128a

  • Ascon XOF / XOFa

• Keyed Message Digest algorithms

  • HMAC

  • KMAC

• Key Derivation Functions

  • HKDF

  • SP800-108 KDF (counter, feedback, double pipelining mode)

  • PBKDF2

• Key Encapsulation Mechanism

  • Kyber Key Encapsulation Mechanism (KEM)

  • Kyber Key Exchange Mechanism (KEX)

  • Kyber Integrated Encryption Schema (IES) - algorithm devised with leancrypto, see kyber_ies.c for full specification

  • Kyber hybrid KEM / KEX with Curve25519

• One Time Pad algorithms

  • HOTP

  • TOTP

• Signature algorithm

  • Dilithium

  • Dilithium hybrid signature operation with Curve25519

• Symmetric algorithms

  • AES: ECB, CBC, CTR, KW

  • ChaCha20

API Documentation

The complete API documentation is provided in the different header files lc_*.h.

Testing

Functional Testing

The command meson test -C build performs a full regression testing of all algorithms and all code paths.

When using the code coverage analysis support enabled by meson setup build -Db_coverage=true followed by meson test -C build and ninja coverage-html -C build, it is shown that almost all code paths in the library are covered (the test code contains error code paths which are not all tested, naturally).

To perform testing of the Linux kernel module of leancrypto, insmod the module leancrypto.ko followed by insmoding all remaining kernel modules found in the linux_kernel directory and review the kernel log via dmesg. After completion of testing, these modules can be removed.

Memory Leak Testing

Using valgrind, the memory leak testing can be applied. Valgrind shows no leaks possible for any code path.

For the Linux kernel, kmemleak can be applied showing no leaks during test execution.

ASAN Testing

Using ASAN address testing with the help of meson, no issues were identified.

Similarly, KASAN can be used for the same type of testing inside the Linux kernel where no issues were identified.

Clang Static Code Analysis

Using the clang-scan tool with the command ninja -C build/ scan-build shows no issues.

Linux Hints

Linux offers the memfd_secret(2) system call which would be used by leancrypto for secure memory allocation, if it is available. This system call, however, is only available when the kernel is booted with securemem.enable=1. With this option enabled, according to the kernel documentation suspend is disabled as long as one or more memory with memfd_secret is in use.

If the memfd_secret is not available, leancrypto will use mlock to protect memory with sensitive data.

ACVP Testing

ACVP certificates covering all ciphers and their implementations testable by NIST:

The testing covered the following platforms:

• x86_64 systems: Intel Tiger Lake i7, Intel Alder Lake i7, AMD Ryzen 9 5950X

• RISC-V system: SiFive Unmatched board with U74 SiFive Freedom U740 SoC

• ARMv7: NXP Cortex-A7 i.MX6ULZ

• ARMv8: Apple M2, Broadcom BCM2711

The test harness is available at https://github.com/smuellerDD/acvpparser covering all algorithm implementations of algorithms that are testable.

Version 0.6.0

• A3770 non-accelerated C cipher implementations

• A3771 AVX2 accelerated cipher implementations

• A3772 4-way SIMD accelerated cipher implementations

• A3773 AVX512 accelerated cipher implementations

• A3774 AES-NI accelerated cipher implementations

• A3775 RISC-V assembler cipher implementations

• A3776 ARMv8 assembler cipher implementations

• A3777 ARMv8 Crypto Extensions cipher implementations

• A3778 ARMv7 NEON cipher implementations

Version 0.7.0

• A4405 non-accelerated C cipher implementations

• A4409 AVX2 accelerated cipher implementations

• A4410 4-way SIMD accelerated cipher implementations

• A4413 AVX512 accelerated cipher implementations

• A4411 AES-NI accelerated cipher implementations

• A4408 RISC-V assembler cipher implementations

• A4407 ARMv8 assembler cipher implementations

• A4412 ARMv8 Crypto Extensions cipher implementations

• A4406 ARMv7 NEON cipher implementations

Version 0.8.0

• A4850 non-accelerated C cipher implementations

• A4866 AVX2 accelerated cipher implementations

• A4867 Intel 4-way SIMD accelerated cipher implementations

• A4864 AVX512 accelerated cipher implementations

• A4865 AES-NI accelerated cipher implementations

• A4851 RISC-V assembler cipher implementations

• A4852 ARMv8 assembler cipher implementations

• A4853 ARMv8 Crypto Extensions cipher implementations

• A4854 ARMv8 2-way SIMD accelerated cipher implementations

• A4860 ARMv7 NEON cipher implementations

Author

Stephan Müller smueller@chronox.de