Frequently Asked Questions (FAQ)


This page lists some of the most common issues and questions that are received by our wolfSSL security experts, along with their responses. This FAQ is useful for solving general questions that pertain to building/implementing wolfSSL.

If this page does not provide an answer to your question, please feel free to check the wolfSSL Manual, or contact us at

To navigate this page, follow the links in the Table of Contents to quickly reach a question, or scroll to the location of the desired question. To return to this point, use either browser's "back" button, scroll back to the top, or follow the link that returns the browser to the top of the page.

1. How do I manage the build configuration for wolfSSL?

Category: Configuration

The MOST common issue we see is a mis-configuration between APP and Library. If you compile the wolfSSL library independant of your application using you MUST include the same configure options in the application as were used in the library.

If building with “./configure” the build system will generate the file <wolf-root>/wolfssl/options.h with all the settings needed for your application. Simply add the lines:

#include <wolfssl/options.h>
#include <wolfssl/wolfcrypt/settings.h>
#include <wolfssl/ssl.h>
/* other wolf headers below */

If building the wolfSSL sources directly the options.h will not contain any generated configuration. In that case our recommended option is to define the preprocessor macro “WOLFSSL_USER_SETTINGS” in your project and create your own “user_settings.h” file. Make sure the file is somewhere in your include path. You can use the same include pattern above, but exclude the options.h.

Here are some example “user_settings.h” you can use for reference:

  • Windows: /IDE/WIN/user_settings.h
  • GCC ARM: /IDE/GCC-ARM/Header/user_settings.h
  • Xcode: /IDE/XCODE/user_settings.h

Return to top of page

2. How do I find the correct CA certificate to load into a client for authenticating a SSL/TLS server?

Category: Certificates

How to find and load the correct CA (root) certificate into a client application or device can be tricky at first.  First, users need to understand how wolfSSL verifies certificate chains. Section 7.3 of the wolfSSL Manual explains wolfSSL’s certificate validation process:

wolfSSL requires that only the top or “root” certificate in a chain to be loaded as a trusted certificate in order to verify a certificate chain. This means that if you have a certificate chain (A -> B -> C), where C is signed by B, and B is signed by A, wolfSSL only requires that certificate A be loaded as a trusted certificate in order to verify the entire chain (A->B->C).

Let’s look at a simple example.  If a server certificate chain looks like this:


| ---- > B

             | ---- > C

The wolfSSL client should already have at least root cert “A” loaded as a trusted root.  When the client receives the server cert chain, it uses the signature of A to verify B, and if B has not been previously loaded into wolfSSL as a trusted root, B gets stored in wolfSSL's internal cert chain (wolfSSL just stores what is necessary to verify a certificate: common name hash, public key and key type, etc.).  If B is valid, then it is used to verify C.

Following this model, as long as root cert "A" has been loaded as a trusted root into the wolfSSL server, the server certificate chain will still be able to be verified if the server sends (A->B->C), or (B->C).  If the server just sends (C), and not the intermediate certificate, the chain will not be able to be verified unless the wolfSSL client has already loaded B as a trusted root.

Return to top of page

3. How do I put my certificate into a buffer?

Category: Certificates

To generate a certificate buffer you will find a perl script <wolfssl-root>/ (short for generate certificate buffers)

  1. You would want to acquire your own certificate and place it in a location that suites your needs. (We keep our test ones in <wolfssl-root>/certs/ directory, feel free to also place your valid ones there also).
  2. Modify the above mentioned perl script and add your new certificate(s) to the appropriate @fileList (1024 for 1024 bit RSA certs, 256 for ECC 256-bit certs... etc)
  3. Re-run that script to re-generate the header file <wolfssl-root>/wolfssl/certs_test.h

You have to run this file manually IE: perl OR ./

Return to top of page


4. How much Flash/RAM does wolfSSL use?

Category: Memory Usage

wolfSSL memory usage depends on how the library is configured when it is compiled and what features you plan on using.  Many options exist to control the amount of memory the library uses.please contact us for the wolfSSL Resource Use document.

The primary factors in peak resource usage are key size and the math library used.  Fast math and a larger key size increases resource utilization.

Return to top of page

5. Is it possible to use no dynamic memory with wolfSSL and/or wolfCrypt?

Category: Memory Usage

wolfSSL provides two options to control the usage of dynamic memory.  You can configure wolfSSL with --enable-static-memory however this is limited to basic TLS connections and currently is not supported in wolfCrypt.  You can also define the macro USER_MALLOC to have wolfSSL use your own malloc function.

Return to top of page

6. How do I build wolfSSL on… (*NIX, Windows, Embedded device)?

Category: Operating Systems

Please see section 2 of the wolfSSL Manual located HERE which covers building wolfSSL

Return to top of page


7. How do I pull wolfSSL into my IDE project? What files and headers do I need?

Category: IDE / Compilers

wolfSSL provides the necessary project files for many popular IDEs.  You can find instructions for these IDEs in the /IDE/ directory of the wolfSSL source.

Include path wolfssl root.

Further documentation on building wolfSSL on various platforms can be found in Section 2.4 wolfSSL Manual.

Return to top of page

8. Do you have benchmarks for my specific platform?

Category: Benchmarks

wolfSSL provides a benchmark application that can be compiled for any platform wolfSSL supports.  The benchmark application will run benchmarks on enabled algorithms. The application source is located in wolfcrypt/benchmark/benchmark.c.  For *nix platforms, the benchmark can be ran using ./wolfcrypt/benchmark/benchmark. The benchmark is compiled by default.

If benchmarking on an embedded platform, define BENCH_EMBEDDED

For more details regarding benchmarking wolfSSL, please reference the wolfSSL and wolfCrypt Benchmarks webpage.

Return to top of page

9. Why are there no common cipher suites found between my client/server when connecting?

Category: Connection Details

Ensure that wolfSSL was configured and built with common cipher suites on both the client and server.  You can add additional cipher suites with configure options. You can view configure options on *nix systems with ./configure --help

To view default cipher suite on *nix system use this command from <wolfssl-root> directory:

./examples/client/client -e

To view default cipher suites on windows system use this command from the directory where client.exe is located:

./client.exe -e

nmap --script ssl-enum-ciphers -p 443

Return to top of page

10. Can I use a smaller maximum I/O record size than 16kB?

Category: Connection Details

TLS specifies a fixed maximum record length of 2^14 bytes (~16kB).  wolfSSL provides two options to use a smaller maximum record size. The first option is to configure wolfSSL with --enable-maxfragment. This requires the client to make an additional call when connecting to a server.  The client needs to use either wolfSSL_CTX_UseMaxFragment or wolfSSL_UseMaxFragment.  The client should use the CTX method if they plan on making multiple connections to the same server.

The other option is to define MAX_RECORD_SIZE.  In order to use this, however, both the client and server needs to have the option set.  If the client is connecting to servers outside of your control, this is not an option to use.

Return to top of page

11. How do I extract a public key from a X.509 certificate?

Category: Certificates

wolfSSL provides this functionality in its public API.  You can call wolfssl_x509_get_pubkey() to return a WOLFSSL_EVP_PKEY pointer.  WOLFSSL_EVP_PKEY is a struct with several data members related to the key.  You can access the key directly from this pointer. The declaration of the struct can be found in <wolfssl/ssl.h>.

Return to top of page

12. Do you have examples of using SSL/TLS or cryptography?

Category: Examples

wolfSSL maintains several examples for using the library on the official wolfSSL GitHub repository.  You can download the examples by cloning the repository at

There are currently examples of using algorithms (3DES, AES, and Camellia), examples of using TLS client and server, wolfSSL CertManager, and signatures and verification.

Return to top of page

13. Why won’t my application connect to a server, I have enabled required ciphers and protocol version…?

Category: Extensions

Some servers require specific TLS extensions and specific ECC curves to be enabled or they will ignore any connection attempt outright regardless of supported ciphers and protocol version. If you are building wolfSSL without the configure script (Makefile project, IDE project, etc), please make sure you have defined HAVE_TLS_EXTENSIONS and HAVE_SUPPORTED_CURVES

Return to top of page