wolfSSL is a small, portable, embedded SSL/TLS library targeted for use by embedded systems developers. It is an open source implementation of TLS (SSL 3.0, TLS 1.0, 1.1, 1.2, 1.3, and DTLS 1.0, 1.2, and 1.3) written in the C programming language. It includes SSL/TLS client libraries and an SSL/TLS server implementation as well as support for multiple APIs, including those defined by SSL and TLS. wolfSSL also includes an OpenSSL compatibility interface with the most commonly used OpenSSL functions.[4][5]
A predecessor of wolfSSL, yaSSL is a C++ based SSL library for embedded environments and real time operating systems with constrained resources.
wolfSSL is currently available for Win32/64, Linux, macOS, Solaris, ESP32, ESP8266, Threadx, VxWorks, FreeBSD, NetBSD, OpenBSD, embedded Linux, Yocto Project, OpenEmbedded, WinCE, Haiku, OpenWrt, iPhone, Android, Nintendo Wii and Gamecube through DevKitPro support, QNX, MontaVista, Tron variants, NonStop OS, OpenCL, Micrium's MicroC/OS-II, FreeRTOS, SafeRTOS, Freescale MQX, Nucleus, TinyOS, TI-RTOS, HP-UX, uTasker, uT-kernel, embOS, INtime, mbed, RIOT, CMSIS-RTOS, FROSTED, Green Hills INTEGRITY, Keil RTX, TOPPERS, PetaLinux, Apache Mynewt, and PikeOS.[6]
The genesis of yaSSL, or yet another SSL, dates to 2004. OpenSSL was available at the time, and was dual licensed under the OpenSSL License and the SSLeay license.[7] yaSSL, alternatively, was developed and dual-licensed under both a commercial license and the GPL.[8] yaSSL offered a more modern API, commercial style developer support and was complete with an OpenSSL compatibility layer.[4] The first major user of wolfSSL/CyaSSL/yaSSL was MySQL.[9] Through bundling with MySQL, yaSSL has achieved extremely high distribution volumes in the millions.
By default, wolfSSL uses the cryptographic services provided by wolfCrypt.[13] wolfCrypt Provides RSA, ECC, DSS, Diffie–Hellman, EDH, NTRU, DES, Triple DES, AES (CBC, CTR, CCM, GCM), Camellia, IDEA, ARC4, HC-128, ChaCha20, MD2, MD4, MD5, SHA-1, SHA-2, SHA-3, BLAKE2, RIPEMD-160, Poly1305, Random Number Generation, Large Integer support, and base 16/64 encoding/decoding. An experimental cipher called Rabbit, a public domain software stream cipher from the EU's eSTREAM project, is also included. Rabbit is potentially useful to those encrypting streaming media in high performance, high demand environments.
wolfCrypt acts as a back-end crypto implementation for several popular software packages and libraries, including MIT Kerberos[14] (where it can be enabled using a build option).