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wolfSSL Embedded SSL/TLS Library

The wolfSSL embedded SSL library (formerly CyaSSL) is a lightweight SSL/TLS library written in ANSI C and targeted for embedded, RTOS, and resource-constrained environments - primarily because of its small size, speed, and feature set. It is commonly used in standard operating environments as well because of its royalty-free pricing and excellent cross platform support. wolfSSL supports industry standards up to the current TLS 1.3 and DTLS 1.3, is up to 20 times smaller than OpenSSL, and offers progressive ciphers such as ChaCha20, Curve25519, Blake2b and Post-Quantum TLS 1.3 groups. User benchmarking and feedback reports dramatically better performance when using wolfSSL over OpenSSL.

wolfSSL is powered by the wolfCrypt cryptography library. Two versions of wolfCrypt have been FIPS 140-2 validated (Certificate #2425 and certificate #3389). FIPS 140-3 validation is in progress. For additional information, visit the wolfCrypt FIPS FAQ or contact

Why Choose wolfSSL?

There are many reasons to choose wolfSSL as your embedded, desktop, mobile, or enterprise SSL/TLS solution. Some of the top reasons include size (typical footprint sizes range from 20-100 kB), support for the newest standards (SSL 3.0, TLS 1.0, TLS 1.1, TLS 1.2, TLS 1.3, DTLS 1.0, DTLS 1.2, and DTLS 1.3), current and progressive cipher support (including stream ciphers), multi-platform, royalty free, and an OpenSSL compatibility API to ease porting into existing applications which have previously used the OpenSSL package. For a complete feature list, see Chapter 4 of the wolfSSL manual.

Notes, Please Read

Note 1

wolfSSL as of 3.6.6 no longer enables SSLv3 by default. wolfSSL also no longer supports static key cipher suites with PSK, RSA, or ECDH. This means if you plan to use TLS cipher suites you must enable DH (DH is on by default), or enable ECC (ECC is on by default), or you must enable static key cipher suites with one or more of the following defines:


Though static key cipher suites are deprecated and will be removed from future versions of TLS. They also lower your security by removing PFS.

When compiling ssl.c, wolfSSL will now issue a compiler error if no cipher suites are available. You can remove this error by defining WOLFSSL_ALLOW_NO_SUITES in the event that you desire that, i.e., you're not using TLS cipher suites.

Note 2

wolfSSL takes a different approach to certificate verification than OpenSSL does. The default policy for the client is to verify the server, this means that if you don't load CAs to verify the server you'll get a connect error, no signer error to confirm failure (-188).

If you want to mimic OpenSSL behavior of having SSL_connect succeed even if verifying the server fails and reducing security you can do this by calling:

wolfSSL_CTX_set_verify(ctx, WOLFSSL_VERIFY_NONE, NULL);

before calling wolfSSL_new();. Though it's not recommended.

Note 3

The enum values SHA, SHA256, SHA384, SHA512 are no longer available when wolfSSL is built with --enable-opensslextra (OPENSSL_EXTRA) or with the macro NO_OLD_SHA_NAMES. These names get mapped to the OpenSSL API for a single call hash function. Instead the name WC_SHA, WC_SHA256, WC_SHA384 and WC_SHA512 should be used for the enum name.

wolfSSL Release 5.6.4 (Oct 30, 2023)

Release 5.6.4 has been developed according to wolfSSL's development and QA process (see link below) and successfully passed the quality criteria.

NOTE: * --enable-heapmath is being deprecated and will be removed by 2024 * Old CyaSSL/CtaoCrypt shim layer was removed in this release (5.6.4)


  • [Medium] A fix was added, but still under review for completeness, for a Bleichenbacher style attack, leading to being able to decrypt a saved TLS connection and potentially forge a signature after probing with a large number of trial connections. This issue is around RSA decryption and affects static RSA cipher suites on the server side, which are not recommended to be used and are off by default. Static RSA cipher suites were also removed from the TLS 1.3 protocol and only present in TLS 1.2 and lower. All padding versions of RSA decrypt are affected since the code under review is outside of the padding processing. Information about the private keys is NOT compromised in affected code. It's recommended to disable static RSA cipher suites and update the version of wolfSSL used if using RSA private decryption alone outside of TLS. The fix is located in this pull request (#6896)

New Feature Additions

  • DTLS 1.3 PQC: support fragmenting the second ClientHello message. This allows arbitrarily long keys to be used, opening up support for all PQC ciphersuites in DTLS 1.3.
  • SM2/SM3/SM4: Chinese cipher support including TLS 1.3 and 1.2 cipher suites. SM2 SP implementation available.
  • Ability to parse ASN1 only with SMIME_read_PKCS7
  • Added support for MemUse Entropy on Windows
  • Added Ada Bindings for wolfSSL
  • Added a PEM example that converts to and from DER/PEM.
  • Added LMS/HSS and XMSS/XMSS^MT wolfcrypt hooks, both normal and verify-only options.
  • Added support for the AES EAX mode of operation
  • Port for use with Hitch ( added
  • Add XTS API's to handle multiple sectors in new port to VeraCrypt

Enhancements and Optimizations

  • Turned on SNI by default on hosts with resources
  • Improved support for Silicon Labs Simplicity Studio and the ERF32 Gecko SDK
  • Thumb-2 and ARM32 Curve25519 and Ed25519 assembly have significantly improved performance.
  • Thumb-2 AES assembly code added.
  • Thumb-2 and ARM32 SP implementations of RSA, DH and ECC have significantly improved performance.
  • Minor performance improvements to SP ECC for Intel x64.
  • AES-XTS assembly code added for Intel x64, Aarch64 and ARM32.
  • Added support for X963 KDFs to ECIES.
  • Added 32-bit type only implementation of AES GMULT using tables.
  • Add support for nginx version 1.25.0
  • Add support for Kerberos version 5 1.21.1
  • Check all CRL entries in case a single issuer has multiple CRL's loaded
  • CRL verify the entire chain including loaded CA's
  • Added example for building wolfSSL as an Apple universal binary framework using configure
  • Sniffer tool now supports decrypting TLS sessions using secrets obtained from a SSLKEYLOGFILE
  • Updates made for EBSNET port
  • Update "--enable-jni" to include additional defines for expanded JNI support. Also includes JCE and JSSE builds under the single enable option now.


  • Fixed error handling when decrypted pre-master secret is too long when using static RSA.
  • Added a fix for keymod use with i.MX RT1170 CAAM blobs
  • Added a fix for AES-GCM use with Petalinux Xilinx
  • Fixed wc_SignatureGenerate_ex to not call verify twice
  • Fixed wolfCrypt FIPS DLL on Win32
  • Fixed TFM math library big-endian reading implementation when a zero length buffer is passed in.
  • Fixed NO_CERT configurations to build correctly.
  • Fixed ARM AES-GCM streaming assembly when –enable-opensslextra defined.
  • Added modulus checks to heap math implementation of mp_exptmod().
  • Fixed Windows assembly code to handle that certain XMM registers are non-volatile.
  • Aarch64 SP ECC implementation of sp_256_mont_dbl_4 has the register list for the assembly code fixed to include all used registers.
  • mp_sqrt_mod_prime fixed to limit the number of iterations of a loop to handle malicious non-prime values being passed in.
  • Ignore session ID's shorter than 32 bytes instead of erroring out

For additional vulnerability information visit the vulnerability page at:

See INSTALL file for build instructions. More info can be found on-line at:


wolfSSL Website

wolfSSL Wiki

FIPS 140-2/140-3 FAQ

wolfSSL Documentation

wolfSSL Manual

wolfSSL API Reference

wolfCrypt API Reference

TLS 1.3

wolfSSL Vulnerabilities

Additional wolfSSL Examples