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]

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Quick Facts Developer(s), Initial release ...

wolfSSL

Developer(s)	Todd Ouska
Initial release	February 19, 2006 (2006-02-19)[1]
Stable release	5.7.0[2]  / 21 March 2024
Repository	github.com/wolfssl/wolfssl
Written in	C
Operating system	Multi-platform
Type	Cryptography library
License	GPL-2.0-or-later or proprietary[3]
Website	www.wolfssl.com

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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 Microsoft Windows, Linux, macOS, Solaris, ESP32, ESP8266, Threadx, VxWorks, FreeBSD, NetBSD, OpenBSD, embedded Linux, Yocto Project, OpenEmbedded, WinCE, Haiku, OpenWrt, iPhone, Android, 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.

In February 2019, Daniel Stenberg, the creator of cURL, was hired by the wolfSSL project to work on cURL.^[10]

The wolfSSL lightweight SSL library implements the following protocols:^[11]

• SSL 3.0, TLS 1.0, TLS 1.1, TLS 1.2, TLS 1.3
• DTLS 1.0, DTLS 1.2, DTLS 1.3
• Extensions: Server Name Indication (SNI), Maximum Fragment Length, Truncated HMAC, Application Layer Protocol Negotiation (ALPN), Extended Master Secret
• Ciphersuites: TLS Secure Remote Password, TLS Pre-Shared Key
• Post-quantum cryptography: QSH (quantum-safe handshake)
• Public Key Cryptography Standards:
  • PKCS #1 - RSA Cryptography
  • PKCS #3 - Diffie-Hellman Key Agreement
  • PKCS #5 - Password-Based Encryption
  • PKCS #7 - Cryptographic Message Syntax (CMS)
  • PKCS #8 - Private-Key Information Syntax
  • PKCS #9 - Selected Attribute Types
  • PKCS #10 - Certificate signing request (CSR)
  • PKCS #11 - Cryptographic Token Interface
  • PKCS #12 - Certificate/Personal Information Exchange Syntax Standard

Protocol Notes:

• SSL 2.0 – SSL 2.0 was deprecated (prohibited) in 2011 by RFC 6176. wolfSSL does not support it.
• SSL 3.0 – SSL 3.0 was deprecated (prohibited) in 2015 by RFC 7568. In response to the POODLE attack, SSL 3.0 has been disabled by default since wolfSSL 3.6.6, but can be enabled with a compile-time option.^[12]

wolfSSL uses the following cryptography libraries:

wolfSSL supports the following certifications:

• Federal Information Processing Standards (FIPS 140)
  • FIPS 140-2^[17]
    • wolfCrypt FIPS Module: 3.6.0 (NIST certificate #2425) - Historical
    • wolfCrypt FIPS Module: 4.0 (NIST certificate #3389) - Historical
• Radio Technical Commission for Aeronautics (RTCA)
  • DO-178C
    • wolfCrypt COTS DO-178C certification kit (DAL A) ^[18]

wolfSSL is dual licensed:

• Licensed under the GPL-2.0-or-later license. This is good for GPL open source projects and evaluation.
• Licensed under a commercial non-GPL license. This comes with additional support and maintenance packages and is priced at 6,000 USD per product or SKU as of 2022.

• Transport Layer Security
• Comparison of TLS implementations
• Comparison of cryptography libraries
• GnuTLS
• Network Security Services
• OpenSSL