How Much Resource Does Your TLS Take?

Adding security to a connection comes at a cost. It takes a little time to perform the crypto operations and some memory gets used during the operations. Not all TLS implementations are equal … how much memory and how much time is lost depends on what TLS library is being used.

Recently OpenSSL came out with their 3.0.0 version and we did a quick collection of runtime memory used. Both to re-collect and make sure wolfSSL has not gotten any unexpected bloat and to check out what OpenSSL has done with their long awaited update. What we found surprised us. To run a simple, single TLS 1.2 connection OpenSSL 3.0.0 took up over 800 KiB of memory where wolfSSL 4.8.1 took up 37.4 KiB. This was collected using the very basic example TLS server from wolfssl-examples/tls/server-tls.c where the functions in it were changed to the OpenSSL versions (i.e. wolfSSL_new -> SSL_new), and changed to run a single connection instead of a loop. First linked to OpenSSL 3.0.0 then to wolfSSL 4.8.1. The memory used during the single connection was collected using Valgrind’s massif tool and then converted into a graph with massif-visualizer.

The memory usage difference between the two libraries is dramatic. A lot of the memory usage with OpenSSL 3.0.0 appears to be surrounding the startup/shutdown code but even when trimming that necessary portion of the runtime memory usage off, it takes over 100 KiB per connection versus wolfSSL’s 13.9 KiB per connection. This makes OpenSSL 3.0.0 difficult if not impossible to be used in some IoT devices and also requires more resources when scaled to large server use cases. Leading to more hardware required and more memory to handle the same number of connections (more $$$).

You may ask though, what about performance? wolfSSL has a SP version that has optimizations for the public key algorithms commonly used in TLS connections. To configure with the “small” version of these optimizations the build “./configure –enable-opensslextra –enable-sp-math-all=small –enable-sp=small” could be used. Recollecting memory usage with the same server-tls.c app linked to the sp small version of wolfSSL used 26.3 KiB. Even less memory than before because along with optimizations for speed some optimizations for memory are also turned on.

For questions about wolfSSL and our resource usage contact