wolfBoot support for the STM32C0

We are adding wolfBoot support for the new STM32C0. This is a low cost MCU similar to the STM32G0 based on a Cortex-M0 (48MHz). It is a very low cost general purpose 32-bit MCU with up to 32KB flash and 12KB RAM.

Our wolfBoot secure bootloader is the only solution available for this platform thanks to our small code size. Most STM32 parts are supported with wolfBoot out of the box. See our video series with ST for a tutorial on using wolfBoot: https://www.wolfssl.com/st-wolfboot-video-series/

See the STM32C0 announcement from ST: https://www.st.com/en/microcontrollers-microprocessors/stm32c0-series.html

We will be demonstrating this at our booth during Embedded World 2023 in Nuremberg, Germany March 14-16.


  • Written in C for bare-metal use
  • Small footprint to run on small embedded devices
  • Memory safety (no malloc/free)
  • Support for on-board or external SPI flash
  • Simple partitioning and header scheme
  • Abstracted HAL design for CPU speed and flash
  • Bootloader handles swapping and loading of partitions
  • Key tools for key generation/import and signing
  • Encrypted updates
  • Delta updates (only differences)

Signature algorithms supported:

  • ECC (SECP256R1,SECP384R1)
  • RSA (2048/3072/4096)
  • ED25519
  • ED448

Firmware image integrity using hash digest:

  • SHA2-256
  • SHA2-384
  • SHA3-384

Flexible partition scheme determined at build-time:

  • Bootloader (10-30KB)
  • Application
  • Update
  • Swap (1 sector)
  • And custom partition ID's

Reliable Firmware update mechanism:

  • Independent from the update transport mechanism
  • Fallback to a previous version when the update fails
  • Resume interrupted swap operations during update, in case of power failure

Support for STM hardware crypto acceleration:

  • ST33TP* TPM 2.0 using wolfTPM

    If interested in trying our wolfBoot on the STM32C0 or curious about post-quantum signature support in wolfBoot please contact facts@wolfssl.com.

KEMTLS Experimentation Via wolfSSL

A new, exciting paper has been released by Ruben Gonzalez from Neodyme AG and Thom Wiggers from Radboud University. They compare post-quantum algorithms in TLS 1.3 and KEMTLS.  KEMTLS is a newly proposed modification to the TLS 1.3 protocol that would eliminate the need for signing operations during a handshake protocol.  Note that a long term KEM public key would be embedded into a leaf certificate so the certificate chain would still need to be verified with a signature scheme.  The team did the work of modifying wolfSSL to support KEMTLS in their own fork of wolfSSL. Their paper can be found at https://eprint.iacr.org/2022/1712 .

The paper concludes that KEMTLS would allow for lower memory consumption.  However, there was no clear winner with regards to handshake times.  In some situations, post-quantum TLS 1.3 was faster, while in other cases KEMTLS did better.  If you are curious about it, please do download the paper.

We would like to thank the authors for the following words:

"WolfSSL is designed to be memory efficient and fast on embedded systems. On top, it already supports TLS 1.3 and has a clean implementation of TLS’s state machine. ...WolfSSL’s crypto provider, called WolfCrypt, has a clean API that can be extended easily."

Here at wolfSSL, we appreciate it when our code quality is noticed.

Are you curious about any other protocols? Our wolfSSL library also supports DTLS 1.2 and recently support for DTLS 1.3 was added.  We support SSH, MQTT and SCEP via our wolfSSH, wolfMQTT and wolfSCEP products. If you are curious, don't be shy! The full source code for all of these products are available for download under open source licenses at https://www.github.com/wolfSSL/. You can also reach out to us for more details at facts@wolfssl.com.

wolfEngine 1.3.0 Released

We’re happy to announce that wolfEngine 1.3.0 has been released! wolfEngine is an OpenSSL engine implementation that helps users migrate to a FIPS-validated cryptography library (wolfCrypt) all while continuing to use OpenSSL.

Version 1.3.0 includes support for RPM packaging, support and tests for OpenSSL HMAC operations to be called with a -1 key length, and updated examples which are compatible with OpenSSL 1.0.2. You can read the full list of changes in the ChangeLog.md on GitHub. For documentation and usage instructions for wolfEngine, visit the wolfEngine User Manual.

If you are interested in a commercial version of wolfEngine or using the wolfCrypt FIPS 140-2 or upcoming 140-3 module in your project, please contact wolfSSL at facts@wolfssl.com with any questions or for more details!

Rust Crate for Post-Quantum TLS 1.3 and wolfSSL

Are you on the bleeding edge of software development and cryptographic protocols? Then you'll appreciate the work that our friends at ExpressVPN have done by creating a rust crate for wolfSSL with bindings into our API.  They have even created a special feature flag called "postquantum" which enables our integration with liboqs. In fact, this feature will automatically bring in the oqs-sys rust crate making the whole setup as simple as could be!

For more details and instructions on how to proceed, please see https://crates.io/crates/wolfssl-sys/ .

Are you interested in more rust bindings?  Are you thinking of using wolfSSL in your rust application? Then we would love to have a conversation with you! Please reach out to us by sending a message to facts@wolfssl.com or your local wolfSSL business director.


DTLS 1.3 support for Post-Quantum Cryptography

Do you want to start using wolfSSL’s DTLS 1.3 implementation?   Want to go even further? 

A great reason to start using our DTLS 1.3 stack is that it also supports post-quantum KEMs, Hybrid KEMs and post-quantum signature schemes.  When it comes time to move to post-quantum standards, support for them will likely come in the newest protocol standards only, so you might as well go to DTLS 1.3 as soon as you can and make sure that post-quantum algorithms and artifacts won’t be a challenge for your system. 

Got questions about the DTLS 1.3 or post-quantum cryptography? Don’t be shy! Send a message to support@wolfssl.com or reach out to your local wolfSSL business director. 

wolfSSL: Hardened By Default

In cryptography when we talk about hardening a library, we mean enabling resistance to timing attacks and cache attacks, using RSA blinding and protecting against glitching.

Enabling and Disabling

Our code has many related macros which can be controlled via configure script flags such as the harden flag and maxstrength flag. When hardening is enabled, the following flags are defined:




When it is disabled, the following flags are defined:



NOTE: hardening is enabled by default and in most cases should NOT be disabled. Later in this post, we will discuss some guidance on this matter.

The “maxstrength” flag is disabled by default because it only allows AEAD-PFS (Authenticated Encryption with Associated Data - Perfect Forward Secrecy) cipher suites which can cause interoperability issues. However, when it is enabled, it defines WOLFSSL_CIPHER_TEXT_CHECK, which protects against glitching attacks. If you want other cipher suites to be available, but also want glitching protection for the relevant ciphersuites, you can add -DWOLFSSL_CIPHER_TEXT_CHECK to your CFLAGS environment variable.

Timing Attack

This requires the adversary to precisely time the logical operations performed by a CPU or other device. By measuring these times the adversary is able to uncover the private data that was used to perform these operations. These kinds of attacks are even practical against well known, generally secure algorithms including RSA and ECC. Such  attacks are thwarted by making cryptographic operations run in a constant amount of time independent of the private key. More information on timing attacks can be found at: https://en.wikipedia.org/wiki/Timing_attack

Cache Attack

Modern processors perform speculative execution and can leave observable side effects due to execution of branches not taken. This can be in the form of memory access patterns which can be seen in the state of the memory cache. These patterns can indicate information about the private key. The adversary would use nefarious means to make a program access arbitrary locations in the program's memory space to get these patterns.  This attack can be mitigated by eliminating branching in cryptographic operations involving the private key.

RSA Blinding

This involves transforming the input just before the RSA private key operations using some random data. After the operation, the reverse of the transform is performed giving the desired output. This prevents an adversary from gaining knowledge about the private key as they don't know the random data that was used to determine the transform and therefore do not know the true input into the RSA private key operation.


Glitching is when the adversary can feed in modified input data into an algorithm and then observe the error behavior to deduce information about the private key. This requires the adversary to have physical access and intimate knowledge of the software and hardware. They would modify the input into the algorithm by physically changing the values of the input in physical memory. This attack can be detected by copying the input to a separate buffer before a cryptographic operation and comparing the input buffer with that separate buffer after the cryptographic operation to ensure it has not changed.

Disabling Hardening

Generally speaking, you should always leave the “harden” flag enabled, however disabling it can give some performance gains. Here are some factors to consider whether it is appropriate to disable it:

  • Are you only dealing with public data and public keys?
  • Do you really need the performance gains?
  • Are you only doing off-line operations where cryptographic operation timings cannot be observed?
  • Are restrictions in place to ensure no physical access to the hardware?
  • Do you have very simple and audited application code and operating system to minimize nefarious code execution?
  • Did you minimize external interaction (ie network, user interface) to prevent nefarious inputs?
  • Do you sanity check all input data?

If you are still not sure about whether you want to enable hardening, then reach out to your wolfSSL business director or send a message to facts@wolfssl.com and let’s start a conversation.

wolfSSL + nuttX initial testing success!

wolfSSL is pleased to announce initial run-time testing of wolfCrypt + NuttX was successfully completed (Crypto algorithm tests and benchmarking) on both BL602 (RISC-V) and NUCLEO-L552ZE-Q (Cortex-M33) targets! wolfSSL engineers are now working on making a publically available drop-in for the NuttX-apps directory that users can take for a spin! The wolfSSL team is very excited about next steps which include but are not limited to:

  • Testing wolfCrypt post-quantum algorithms in NuttX
  • Testing client/server TLS 1.2 and TLS 1.3 connections in NuttX
  • Testing FIPS functionality in NuttX
  • Publishing benchmark results to our website

Console output from tests run on the RISC-V BL602 target:

NuttShell (NSH)

nsh> wolfcrypt_test


 wolfSSL version 5.5.4


error    test passed!

MEMORY   test passed!

base64   test passed!

asn      test passed!

RANDOM   test passed!

MD5      test passed!

SHA      test passed!

SHA-256  test passed!

Hash     test passed!

HMAC-MD5 test passed!

HMAC-SHA test passed!

HMAC-SHA256 test passed!

DES      test passed!

DES3     test passed!

AES      test passed!

AES192   test passed!

AES256   test passed!

RSA      test passed!

DH       test passed!

PWDBASED test passed!

ECC      test passed!

ECC buffer test passed!

logging  test passed!

time test passed!

mutex    test passed!

memcb    test passed!

Test complete

Exiting main with return code: 0

Have any other ideas or Proof of Concepts you would like us to consider? Please don’t hesitate to reach out to support@wolfssl.com with suggestions for our team!