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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 5.7.0 (Mar 20, 2024)

Release 5.7.0 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 end of 2024

NOTE: In future releases, --enable-des3 (which is disabled by default) will be insufficient in itself to enable DES3 in TLS cipher suites. A new option, --enable-des3-tls-suites, will need to be supplied in addition. This option should only be used in backward compatibility scenarios, as it is inherently insecure.

NOTE: This release switches the default ASN.1 parser to the new ASN template code. If the original ASN.1 code is preferred define WOLFSSL_ASN_ORIGINAL to use it. See PR #7199.


  • [High] CVE-2024-0901 Potential denial of service and out of bounds read. Affects TLS 1.3 on the server side when accepting a connection from a malicious TLS 1.3 client. If using TLS 1.3 on the server side it is recommended to update the version of wolfSSL used. Fixed in this GitHub pull request

  • [Med] CVE-2024-1545 Fault Injection vulnerability in RsaPrivateDecryption function that potentially allows an attacker that has access to the same system with a victims process to perform a Rowhammer fault injection. Thanks to Junkai Liang, Zhi Zhang, Xin Zhang, Qingni Shen for the report (Peking University, The University of Western Australia)." Fixed in this GitHub pull request

  • [Med] Fault injection attack with EdDSA signature operations. This affects ed25519 sign operations where the system could be susceptible to Rowhammer attacks. Thanks to Junkai Liang, Zhi Zhang, Xin Zhang, Qingni Shen for the report (Peking University, The University of Western Australia). Fixed in this GitHub pull request

New Feature Additions

  • Added --enable-experimental configure flag to gate out features that are currently experimental. Now liboqs, kyber, lms, xmss, and dual-alg-certs require the --enable-experimental flag.


  • Experimental framework for using wolfSSL’s XMSS implementation (PR 7161)
  • Experimental framework for using wolfSSL’s LMS implementation (PR 7283)
  • Experimental wolfSSL Kyber implementation and assembly optimizations, enabled with --enable-experimental --enable-kyber (PR 7318)
  • Experimental support for post quantum dual key/signature certificates. A few known issues and sanitizer checks are in progress with this feature. Enabled with the configure flags --enable-experimental --enable-dual-alg-certs (PR 7112)
  • CryptoCb support for PQC algorithms (PR 7110)


  • The Linux kernel module now supports registration of AES-GCM, AES-XTS, AES-CBC, and AES-CFB with the kernel cryptosystem through the new --enable-linuxkm-lkcapi-register option, enabling automatic use of wolfCrypt implementations by the dm-crypt/luks and ESP subsystems. In particular, wolfCrypt AES-XTS with –enable-aesni is faster than the native kernel implementation.
  • CryptoCb hook to one-shot CMAC functions (PR 7059)
  • BER content streaming support for PKCS7_VerifySignedData and sign/encrypt operations (PR 6961 & 7184)
  • IoT-Safe SHA-384 and SHA-512 support (PR 7176)
  • I/O callbacks for content and output with PKCS7 bundle sign/encrypt to reduce peak memory usage (PR 7272)
  • Microchip PIC24 support and example project (PR 7151)
  • AutoSAR shim layer for RNG, SHA256, and AES (PR 7296)
  • wolfSSL_CertManagerUnloadIntermediateCerts API to clear intermediate certs added to certificate store (PR 7245)
  • Implement SSL_get_peer_signature_nid and SSL_get_peer_signature_type_nid (PR 7236)

Enhancements and Optimizations

  • Remove obsolete user-crypto functionality and Intel IPP support (PR 7097)
  • Support for RSA-PSS signatures with CRL use (PR 7119)
  • Enhancement for AES-GCM use with Xilsecure on Microblaze (PR 7051)
  • Support for crypto cb only build with ECC and NXP CAAM (PR 7269)
  • Improve liboqs integration adding locking and init/cleanup functions (PR 7026)
  • Prevent memory access before clientSession->serverRow and clientSession->serverIdx are sanitized (PR 7096)
  • Enhancements to reproducible build (PR 7267)
  • Update Arduino example TLS Client/Server and improve support for ESP32 (PR 7304 & 7177)
  • XC32 compiler version 4.x compatibility (PR 7128)
  • Porting for build on PlayStation 3 and 4 (PR 7072)
  • Improvements for Espressif use; SHA HW/SW selection and use on ESP32-C2/ESP8684, wolfSSL_NewThread() type, component cmake fix, and update TLS client example for ESP8266 (PR 7081, 7173, 7077, 7148, 7240)
  • Allow crypto callbacks with SHA-1 HW (PR 7087)
  • Update OpenSSH port to version 9.6p1(PR 7203)
  • ARM Thumb2 enhancements, AES-GCM support for GCM_SMALL, alignment fix on key, fix for ASM clobber list (PR 7291,7301,7221)
  • Expand heap hint support for static memory build with more x509 functions (PR 7136)
  • Improving ARMv8 ChaCha20 ASM (alignment) (PR 7182)
  • Unknown extension callback wolfSSL_CertManagerSetUnknownExtCallback added to CertManager (PR 7194)
  • Implement wc_rng_new_ex for use with devID’s with crypto callback (PR 7271)
  • Allow reading 0-RTT data after writing 0.5-RTT data (PR 7102)
  • Send alert on bad PSK binder error (PR 7235)
  • Enhancements to CMake build files for use with cross compiling (PR 7188)


  • Fix for checking result of MAC verify when no AAD is used with AES-GCM and Xilinx Xilsecure (PR 7051)
  • Fix for Aria sign use (PR 7082)
  • Fix for invalid dh_ffdhe_test test case using Intel QuickAssist (PR 7085)
  • Fixes for TI AES and SHA on TM4C with HW acceleration and add full AES GCM and CCM support with TLS (PR 7018)
  • Fixes for STM32 PKA use with ECC (PR 7098)
  • Fixes for TLS 1.3 with crypto callbacks to offload KDF / HMAC operation (PR 7070)
  • Fix include path for FSP 3.5 on Renesas RA6M4 (PR 7101)
  • Siphash x64 asm fix for use with older compilers (PR 7299)
  • Fix for SGX build with SP (PR 7308)
  • Fix to Make it mandatory that the cookie is sent back in new ClientHello when seen in a HelloRetryRequest with (PR 7190)
  • Fix for wrap around behavior with BIO pairs (PR 7169)
  • OCSP fixes for parsing of response correctly when there was a revocation reason and returning correct error value with date checks (PR 7241 & 7255)
  • Fix build with NO_STDIO_FILESYSTEM and improve checks for XGETENV (PR 7150)
  • Fix for DTLS sequence number and cookie when downgrading DTLS version (PR 7214)
  • Fix for write_dup use with chacha-poly cipher suites (PR 7206)
  • Fix for multiple handshake messages in one record failing with OUT_OF_ORDER_E when downgrading from TLS 1.3 to TLS 1.2 (PR 7141)
  • Fix for AES ECB build with Thumb and alignment (PR 7094)
  • Fix for negotiate handshake until the end in wolfSSL_read/wolfSSL_write if hitting an edge case with want read/write (PR 7237)

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

Directory structure

├── certs   [Certificates used in tests and examples]
├── cmake   [Cmake build utilities]
├── debian  [Debian packaging files]
├── doc     [Documentation for wolfSSL (Doxygen)]
├── Docker  [Prebuilt Docker environments]
├── examples    [wolfSSL examples]
│   ├── asn1    [ASN.1 printing example]
│   ├── async   [Asynchronous Cryptography example]
│   ├── benchmark   [TLS benchmark example]
│   ├── client  [Client example]
│   ├── configs [Example build configurations]
│   ├── echoclient  [Echoclient example]
│   ├── echoserver  [Echoserver example]
│   ├── pem [Example for convert between PEM and DER]
│   ├── sctp    [Servers and clients that demonstrate wolfSSL's DTLS-SCTP support]
│   └── server  [Server example]
├── IDE     [Contains example projects for various development environments]
├── linuxkm [Linux Kernel Module implementation]
├── m4      [Autotools utilities]
├── mcapi   [wolfSSL MPLAB X Project Files]
├── mplabx  [wolfSSL MPLAB X Project Files]
├── mqx     [wolfSSL Freescale CodeWarrior Project Files]
├── rpm     [RPM packaging metadata]
├── RTOS
│   └── nuttx   [Port of wolfSSL for NuttX]
├── scripts [Testing scripts]
├── src     [wolfSSL source code]
├── sslSniffer  [wolfSSL sniffer can be used to passively sniff SSL traffic]
├── support [Contains the pkg-config file]
├── tests   [Unit and configuration testing]
├── testsuite   [Test application that orchestrates tests]
├── tirtos  [Port of wolfSSL for TI RTOS]
├── wolfcrypt   [The wolfCrypt component]
│   ├── benchmark   [Cryptography benchmarking application]
│   ├── src         [wolfCrypt source code]
│   │   └── port    [Supported hardware acceleration ports]
│   └── test        [Cryptography testing application]
├── wolfssl [Header files]
│   ├── openssl [Compatibility layer headers]
│   └── wolfcrypt   [Header files]
├── wrapper [wolfSSL language wrappers]
└── zephyr  [Port of wolfSSL for Zephyr RTOS]