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In addition, wolfSSL now has a support-specific blog page dedicated to answering some of the more commonly received support questions.

wolfSSL Enforces Stack Usage Reduction

Understanding the stack and the heap are fundamental steps for all software developers. The importance of such understanding is inversely proportional to the amount of memory available on the platform, as both compete for a piece of the total memory space available on a system.

In some cases the developer has the choice of when to use one (either the stack or heap) more than the other. In other cases, a scenario may force the developer to work with minimal use of the stack, the heap, or both.

With this in mind, wolfSSL is introducing a new build option in CyaSSL. Developers can now choose a CyaSSL build that best matches their needs of using more stack and less heap OR more heap and less stack. This process is being accomplished by the refactoring of the CyaSSL code. Currently 90% of the encryption layer has been refactored to use the new option.

Small stack usage is not enabled by default. To enable it users must use the option “–enable-small-stack” when configuring the CyaSSL build as in the following example:

./configure –enable-small-stack [other options]

For users who don`t use CyaSSL`s configure script for compilation, smaller stack usage is not enabled by default. In this case, users will need to add the compiler directive CYASSL_SMALL_STACK in config.h file or settings.h to enjoy its benefits as in the following example:




If you have any questions about stack usage with CyaSSL please let us know at

wolfSSL with TLS 1.3

Hi!  Some of you know that the IETF working group on TLS is creating the specification for TLS 1.3.  We plan to upgrade wolfSSL to the TLS 1.3 specification as soon as the spec is finalized, or even close to finalized.  We are always aggressive with implementing the new TLS specifications, because we like to supply the community with a good test bed.  We did a great job getting TLS 1.2 out right away, as well as DTLS 1.2, and the community appreciated the effort.  We plan to continue our tradition of being quick with new protocol level changes.  

If you`re interested in what TLS 1.3 thinking is so far, then look here:  If you have TLS 1.3 questions or comments, you are welcome to email us at or call us at +1 425 245 8247.

wolfSSL 3.0.0 Released

The new release of wolfSSL, v3.0.0, is now ready to download from our website.  New features include:

– FIPS release candidate
– X.509 improvements that address items reported by Suman Jana with security researchers at UT Austin and UC Davis
– Small stack size improvements, –enable-smallstack. Offloads large local variables to the heap. (Note this is not complete.)
– Updated AES-CCM-8 cipher suites to use approved suite numbers.

Please see the README and our on-line documentation for more information or feel free to contact us.

ChaCha20 and Poly1305 for wolfSSL TLS

Hi!  We`ve scheduled ourselves to implement ChaCha20 and Poly1305 into wolfSSL this summer.  If you`re learning about what these are, see these links:

We`re excited about this addition to our code.  If you have comments, questions, or need it in our code sooner than this summer, then let us know!  We can be reached at or by phone at +1 425 245 8247.

wolfSSL JNI 1.1.0 Released

Version 1.1.0 of wolfSSL JNI is now available for download. wolfSSL JNI provides Java applications with a convenient Java API to the widely-used CyaSSL lightweight SSL/TLS library, including support for TLS 1.2 and DTLS 1.2.

This release contains bug fixes and features including:

– Updated support for CyaSSL, tested against CyaSSL 2.9.4
– Updated example certificates and CRLs for use with the included example client and server applications
– Test framework modification which now expects the user to have JUnit JARs installed on the development platform
– Updated unit tests and conversion from JUnit3 to JUnit4
– Android NDK support
– CRL monitor is now optional in server mode

Additional information regarding using wolfSSL JNI with Android NDK-based applications will follow in a separate post. wolfSSL JNI 1.1.0 can be downloaded from the wolfSSL download page and the wolfSSL JNI Manual can be found here.

OpenBSD team is refactoring OpenSSL

The OpenBSD team is refactoring OpenSSL, which is admirable work.  You can see their progress at

If you read the OpenSSL Rampage blog, you can see that they have their work cut out for them.  The OpenSSL code base is very old, and has had literally hundreds of unknown hands making changes over its 20+ year lifespan.  

The OpenSSL Heartbleed bug has been motivating for a lot of developers, which is probably Heartbleed`s only positive side effect.  As the creators of wolfSSL, a modern clean room implementation of SSL/TLS, we`ve been hearing from a lot of OpenSSL consumers that want to make a change.  They`ve had enough of working with a code base held together with rubber bands and twine.  Here`s why we think OpenSSL users should consider a switch to wolfSSL instead of patching, re-factoring, and hoping:

1.  wolfSSL is clean room developed, which means that we don`t use any OpenSSL code in our implementation of SSL/TLS.  We can point to every developer that has touched a line of our code base.  

2.  Switching from OpenSSL to wolfSSL can be relatively easy.  We usually estimate 1-4 weeks for a project where we rip and replace OpenSSL for wolfSSL.  

3.  If you`re making the switch, we`ll support you, whether you`re an open source project or a commercial user.  

4.  Our code is newer, more modern, and clean.  You should be able to understand the security code plugged into your application, and we think ours is a quick read for competent C/C++ programmers.

5.  We support an OpenSSL compatibility layer which supports the 400 or so most used functions in OpenSSL.  We`ll help you if you need extensions to the layer.

If you have questions, thoughts, or comments to share with us, please email us at, or call us at +1 425 245 8247.

Common Terms and Types in wolfSSL Lightweight SSL

If you are using or thinking about using the wolfSSL lightweight SSL/TLS library in your application or project, it’s oftentimes helpful to get a general overview of some of the terms and types which are used in a simple wolfSSL connection. Below we have included a general summary of these types.

1) socket: wolfSSL uses the type SOCKET_T to allow different TCP stacks to be used.

2) SSL Context:  wolfSSL uses the type CYASSL_CTX*.  This is either a client context or a server context.  Multiple SSL connections can be created from a single CYASSL_CTX*.  The context holds CA certificates, keys, and options for the connections that will be created from it.

3) SSL Connection:  wolfSSL uses the type CYASSL* to represent a single SSL connection.  This object is created from a parent CYASSL_CTX*.  It may contain a SOCKET_T if the underlying I/O is socket based, but that is not a requirement. With wolfSSL’s I/O callbacks a memory buffer, file, or event handler may be used instead.

1) SSL Session:  wolfSSL uses the type CYASSL_SESSION*.  Each time a full SSL handshake is done on a CYASSL* Connection object a new CYASSL_SESSION* is created.  A single CYASSL_SESSION* can later be used to do session resumption on multiple different CYASSL* connections.

For example, let`s say a browser has 3 tabs open to a simple secure site.  The browser would need:

1 CYASSL_CTX* client context with CA certificates loaded.

3 SOCKET_T sockets, 1 for each tab.

3 CYASSL* connections, one for each tab.  Each connection owns one of the 3 unique SOCKET_T but was created from the same CYASSL_CTX*.

1 CYASSL_SESSION* was created from the first tab.  The 2nd and 3rd tab would use the initial CYASSL_SESSION* to do session resumption with their respective CYASSL* connections.

Code wise, to retrieve a session the application would just call wolfSSL_get_session() before ending the connection with wolfSSL_shutdown().

CYASSL_SESSION* mySession = wolfSSL_get_session(ssl_conn1);

To later use that session on a new CYASSL connection (ssl_conn2), do:

wolfSSL_set_session(ssl_conn2, mySession);

before calling wolfSSL_connect().  Connection 2 will attempt session resumption.

For more detailed information, the wolfSSL API reference discusses each function in more detail:

The wolfSSL example client (examples/client/client.c in the general wolfSSL download) does session resumption if the user passes -r to the command line.  If you search for get_session and set_session you should see right where it`s used.

wolfSSL Security Advisory: April 9, 2014

Issue #1 (Memory  Corruption)

CVE-ID:  CVE-2014-2896
Product: CyaSSL
Vendor: wolfSSL Inc.
Affected Versions: CyaSSL 2.9.0 and previous versions
Vulnerability Type:  Improper Input Validation (CWE-20)

Description: The TLS and DTLS implementations in wolfSSL CyaSSL before 2.9.4 lack a buffer length check in DoAlert(), possibly allowing an attacker to set the read index by up to 2 bytes past the length of the input buffer. This could result in memory corruption or a possible out-of-bounds read.

Thanks to Ivan Fratric of the Google Security Team for discovering this  bug.

Issue #2 (Out of bounds read)

CVE-ID: CVE-2014-2897
Product: CyaSSL
Vendor: wolfSSL Inc.
Affected Versions: CyaSSL 2.5.0 – CyaSSL 2.9.0
Vulnerability Type: Cryptographic Issues  (CWE-310)

Description: The SSL version 3 HMAC calculation does not check the padding length for a verify failure because many implementations get this wrong. But the length should still be checked to prevent an out-of-bounds read.

Thanks to Ivan Fratric of the Google Security Team for discovering and reporting this bug.

Issue #3 (Dangerous Default Behavior, out of bounds read)

CVE-ID: CVE-2014-2898
Product: CyaSSL
Vendor: wolfSSL Inc.
Affected Versions: CyaSSL 2.9.0 and previous versions
Vulnerability Type: Unchecked Error Condition (CWE-391)

Description: A user who repeatedly calls CyaSSL_read() without checking the return code can cause an out-of-bound memory access in an error case such as MAC verification failure.

Thanks to Ivan Fratric of the Google Security Team for discovering and reporting this bug.

Issue #4 (NULL pointer dereference)

CVE-ID: CVE-2014-2899
Product: CyaSSL
Vendor: wolfSSL Inc.
Affected Versions: CyaSSL 2.9.0 and previous versions
Vulnerability Type: Improper Input Validation (CWE-20)

Description: A user requesting the peer certificate in a certificate parsing failure case can cause a NULL-pointer dereference. Likewise, if an SSL client receives a client_key_exchange message a NULL-pointer dereference happens if the client does not have the peer’s ephemeral key.

Thanks to Ivan Fratric of the Google Security Team for discovering and reporting this bug.

Issue #5 (Unknown Critical Certificate Extension Allowed)

CVE-ID: CVE-2014-2900
Product: CyaSSL
Vendor: wolfSSL Inc.
Affected Versions: CyaSSL 2.9.0 and previous versions
Vulnerability Type: Improper Input Validation (CWE-20)

Description: Certificate validation must fail if unknown critical extensions are present in the certificate. CyaSSL previously accepted certificates with unknown critical extensions by default.

Thanks to Suman Jana and the security researchers at UT Austin and UC Davis for discovering and reporting this bug.

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