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AWS SigV4 Library

API Documentation Pages for current and previous releases of this library can be found here

The AWS SigV4 Library is a standalone library for generating authorization headers and signatures according to the specifications of the Signature Version 4 signing process. Authorization headers are required for authentication when sending HTTP requests to AWS. This library can optionally be used by applications sending direct HTTP requests to AWS services requiring SigV4 authentication. This library has no dependencies on any additional libraries other than the standard C library. This library is distributed under the MIT Open Source License.

This library has gone through code quality checks including verification that no function has a GNU Complexity score over 8, and checks against deviations from mandatory rules in the MISRA coding standard. Deviations from the MISRA C:2012 guidelines are documented under MISRA Deviations. This library has also undergone static code analysis using Coverity static analysis, and validation of memory safety through the CBMC automated reasoning tool.

See memory requirements for this library here.

AWS SigV4 v1.2.0 source code is part of the FreeRTOS 202210.00 LTS release.

AWS SigV4 Library Config File

The AWS SigV4 library exposes build configuration macros that are required for building the library. A list of all the configurations and their default values are defined in sigv4_config_defaults.h. To provide custom values for the configuration macros, a config file named sigv4_config.h can be provided by the application to the library.

By default, a sigv4_config.h config file is required to build the library. To disable this requirement and build the library with default configuration values, provide SIGV4_DO_NOT_USE_CUSTOM_CONFIG as a compile time preprocessor macro.

Thus, the SigV4 library can be built by either:

  • Defining a sigv4_config.h file in the application, and adding it to the include directories list of the library.


  • Defining the SIGV4_DO_NOT_USE_CUSTOM_CONFIG preprocessor macro for the library build.

Building the SigV4 Library

The sigv4FilePaths.cmake file contains information of all the source files and header include paths required to build the SigV4 library.

As mentioned in the previous section, either a custom config file (i.e. sigv4_config.h) or SIGV4_DO_NOT_USE_CUSTOM_CONFIG macro needs to be provided to build the SigV4 library.

To use CMake, please refer to the sigV4FilePaths.cmake file, which contains the relevant information regarding source files and header include paths required to build this library.

Building Unit Tests

Platform Prerequisites

  • For running unit tests:
    • C90 compiler like gcc.
    • CMake 3.13.0 or later.
    • Ruby 2.0.0 or later is additionally required for the CMock test framework (that we use).
  • For running the coverage target, gcov and lcov are additionally required.

Steps to build Unit Tests

  1. Go to the root directory of this repository.

  2. Run the cmake command: cmake -S test -B build -DUNITTEST=ON.

  3. Run this command to build the library and unit tests: make -C build all.

  4. The generated test executables will be present in build/bin/tests folder.

  5. Run cd build && ctest to execute all tests and view the test run summary.


To learn more about CBMC and proofs specifically, review the training material here.

The test/cbmc/proofs directory contains CBMC proofs.

In order to run these proofs you will need to install CBMC and other tools by following the instructions here.

Reference examples

The AWS IoT Embedded C-SDK repository contains HTTP demos showing the use of the AWS SigV4 Library on a POSIX platform to authenticate HTTP requests to AWS S3 service.

Generating documentation

The Doxygen references found in this repository were created using Doxygen version 1.9.2. To generate these Doxygen pages, please run the following command from the root of this repository:

doxygen docs/doxygen/config.doxyfile


See for information on contributing.