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TLS 1.3 Performance Analysis – Pre-Shared Key (PSK)

TLS 1.3 has a different handshake flow when using pre-shared keys and this impacts performance. This is the third part of six blogs discussing the performance differences observed between TLS 1.2 and TLS 1.3 in wolfSSL and how to make the most of them in your applications. This blog discusses how and why PSK handshakes are only similar in speed generally but faster when using DH style key exchange.

For TLS 1.2, handshakes using PSK are defined in a separate document (RFC 4279). In order to fit in with the existing flow, a full handshake is performed. In TLS 1.3, PSK handshakes are the same as resumption handshakes. Therefore there is one less round-trip required for TLS 1.3.

This change in flow has a significant impact on the performance of TLS 1.3. The amount of hashing and encryption/decryption has increased but losing a round-trip means that using PSK without a DH style key exchange is only slightly slower. On higher latency networks, the difference is trivial and the savings great.

In TLS 1.3 using DH or ECDH with PSK results in the following handshake operations.

So, the secret is calculated on the server after the ServerHello is sent. This means that the processing of the ServerHello and secret calculation on the client is happening at the same time relative to the server calculating the secret. The parallel secret generation resulted in, with client and server running on the same computer, TLS 1.3 being about 25% faster than TLS 1.2 when using DH. Using ECDH with P-256, TLS 1.3 is about 15% faster.

It is clear that using pre-shared keys in a secure way, with DH style key exchange, is faster with TLS 1.3 in wolfSSL. The next blog will discuss use cases that result in the removal of a key generation from the list of expensive cryptographic operations in TLS 1.3.

Part 1 (TLS 1.3 Performance – Resumption)
Part 2 (TLS 1.3 Performance – Full Handshake)

For more information regarding wolfSSL performance or usage of PSK, please contact facts@wolfssl.com.

Differences between TLS 1.2 and TLS 1.3 (#TLS13)

wolfSSL's embedded SSL/TLS library has included support for TLS 1.3 since early releases of the TLS 1.3 draft. Since then, wolfSSL has remained up-to-date with the TLS 1.3 specification. In this post, the major upgrades of TLS 1.3 from TLS 1.2 are outlined below:

TLS 1.3

This protocol is defined in RFC 8446. TLS 1.3 contains improved security and speed. The major differences include:

  • The list of supported symmetric algorithms has been pruned of all legacy algorithms. The remaining algorithms all use Authenticated Encryption with Associated Data (AEAD) algorithms.
  • A zero-RTT (0-RTT) mode was added, saving a round-trip at connection setup for some application data at the cost of certain security properties.
  • Static RSA and Diffie-Hellman cipher suites have been removed; all public-key based key exchange mechanisms now provide forward secrecy.
  • All handshake messages after the ServerHello are now encrypted.
  • Key derivation functions have been re-designed, with the HMAC-based Extract-and-Expand Key Derivation Function (HKDF) being used as a primitive.
  • The handshake state machine has been restructured to be more consistent and remove superfluous messages.
  • ECC is now in the base spec  and includes new signature algorithms. Point format negotiation has been removed in favor of single point format for each curve.
  • Compression, custom DHE groups, and DSA have been removed, RSA padding now uses PSS.
  • TLS 1.2 version negotiation verification mechanism was deprecated in favor of a version list in an extension.
  • Session resumption with and without server-side state and the PSK-based ciphersuites of earlier versions of TLS have been replaced by a single new PSK exchange.

More information about the TLS 1.3 protocol can be found here: https://www.wolfssl.com/docs/tls13/. Additionally, please contact facts@wolfssl.com for any questions.

OpenSSL Compatibility Layer Expansion

Recently, wolfSSL released version 4.0.0 of the wolfSSL embedded SSL/TLS library. This new version includes many new port/feature additions, maintenance updates, and a couple bug fixes. Among those new feature additions includes multiple new API added to wolfSSL's OpenSSL compatibility layer! The compatibility layer is a series of commonly used and essential API that users can utilize to transition from OpenSSL to wolfSSL. The function names are redefined as their wolfSSL counterparts, which have similar signatures and output to their OpenSSL counterparts.

The list of new compatibility API included with the most recent release include the following:

  • BN_Init
  • EVP_Digest
  • EVP_MD_CTX_block_size
  • EVP_MD_CTX_size
  • EVP_PKEY_assign_EC_KEY
  • EVP_PKEY_assign_RSA

The list of OpenSSL compatibility API that were added in the release prior can be found here: https://www.wolfssl.com/openssl-compatibility-layer-expansion-2/

wolfSSL also provides support for TLS 1.3! More information can be found here: https://www.wolfssl.com/docs/tls13/.

wolfSSL is available for download at the wolfSSL download page here (https://www.wolfssl.com/download/), or through a git-clone of the wolfSSL repository here (https://github.com/wolfssl/wolfssl.git).

For more information about wolfSSL or porting from OpenSSL, please contact facts@wolfssl.com.

wolfSSL Adds Support for the Deos Safety Critical RTOS

Are you a user of Deos?  If so, you will be happy to know that wolfSSL recently added support for Deos RTOS and added TLS client/server examples to the wolfSSL embedded SSL/TLS library for Deos!

Deos is an embedded RTOS used for safety-critical avionics applications on commercial and military aircraft. Certified to DO-178C DAL A, the time and space partitioned RTOS features deterministic real-time response and employs patented “slack scheduling” to deliver higher CPU utilization.

The Deos port in wolfSSL is activated by using the "WOLFSSL_DEOS" macro. For instructions on how to build and run the examples on your projects, please see the “<wolfssl-root>/IDE/ECLIPSE/DEOS/README” file.  This support is currently located in our GitHub master branch, and will roll into the next stable release of wolfSSL as well.

wolfSSL provides support for the latest and greatest version of the TLS protocol, TLS 1.3! Using the wolfSSL port with your device running Deos will allow your device to connect to the internet in one of the most secure ways possible.

For more information, please contact facts@wolfssl.com.

Resources
The most recent version of wolfSSL can be downloaded from our download page, here: https://www.wolfssl.com/download/
wolfSSL GitHub repository: https://github.com/wolfssl/wolfssl.git
wolfSSL support for TLS 1.3: https://www.wolfssl.com/docs/tls13/
Deos RTOS homepage: https://www.ddci.com/category/deos/

wolfSSH Port for µC/OS-III

At wolfSSL, we currently have a wolfSSH port to µC/OS-III in the works! µC/OS-III is a highly portable and scalable real-time kernel. Designed for ease of use on a huge number of CPU architectures, these kernels are a key component of the µC/OS real-time operating system. The features of this kernel allow it to pair nicely with the wolfSSH SSHv2 library, resulting in the maximization of the best possible encryption, speed, and strength while simultaneously allowing for minimal resource usage.

Other features that are readily available and currently supported by wolfSSH include SCP, SFTP, client authentication via RSA keys or passwords, and more!

More information about the wolfSSH library: https://www.wolfssl.com/products/wolfssh/

For more information not included, please contact facts@wolfssl.com.

wolfSSL’s Effective Timing Resistance

In cryptography and encryption, timing can be an unconsidered element of the security for various operations. However, if an encryption library is built without considering timing or the possible attacks that a malicious agent could execute with timing attacks, then that encryption library could be vulnerable to multiple different attacks that have occurred or can occur. An actual timing attack requires the agent to precisely time the logical operations performed by a CPU or other device, and by measuring these times is able to construct the sensitive data that was used to perform these operations. These kinds of attacks are even practical against well known, generally secure algorithms including RSA, DSA, and other signature algorithms.

When it comes to the wolfCrypt crypto engine, there are features in place by default to protect against timing attacks. Although these features are enabled by default, to ensure that wolfSSL's timing resistance is enabled, users can either enable it through wolfSSL's configure script or manually define the relevant preprocessor defines. The option "--enable-harden" can be passed to configure to enable both timing resistance and RSA blinding. Macros that can be manually defined are listed below:

ECC_TIMING_RESISTANT /* define to enable timing resistance in ECC */
TFM_TIMING_RESISTANT /* define to enable timing resistance in underlying
                        fastmath math library */

More information on timing attacks can be found here: https://en.wikipedia.org/wiki/Timing_attack

For more information about the wolfSSL embedded SSL/TLS library or other security features offered, please contact facts@wolfssl.com.  wolfSSL also supports TLS 1.3!

TLS 1.3 Performance Analysis – Full Handshake

Significant changes from TLS 1.2 have been made in TLS 1.3 that are targeted at performance. This is the second part of six blogs discussing the performance differences observed between TLS 1.2 and TLS 1.3 in wolfSSL and how to make the most of them in your applications. This blog discusses the performance differences with regard to full handshake with server authentication using certificates.

Let’s start with a look at the TLS 1.2 full handshake performing server-only authentication with certificates below.

A TLS 1.3 full handshake (without HelloRetryRequest) performing server-only authentication with certificates is below.

Notice that there is one less round trip until Application Data can be sent in TLS 1.3 as compared to TLS 1.2. This significantly improves performance especially on high latency networks. But, there is another source of performance improvement arising from the ordering of the handshake messages and when lengthy cryptographic operations are performed.

In the TLS handshake, the server waits on the ClientHello and then sends handshake messages as it produces them in separate packets. When packets are sent is dependent on the amount of processing required to produce the data. For example, to copy a chain of certificates into the Certificate messages is quick, while generating a TLS 1.2 ServerKeyExchange message is slow as it requires multiple public key operations.

The client receives the messages at various time deltas and also requires differing amounts of processing. For example, the Certificate message is likely to require at least one signature verification operation on the leaf certificate. This asymmetric processing of messages means that some handshake messages will be processed on arrival and some will have to wait for processing of previous messages to be completed.

The table below restates the TLS 1.2 handshake but includes processing of messages and the major cryptographic operations that are performed. Operations are on the same line if the they are performed at the same time relative to network latency.

From this we can see that for RSA, where Verify is very fast relative to Sign, a TLS 1.2 handshake is dependent on: 2 x Key Gen, 2 x Secret Gen, 1 x Sign and 1 x Verify. For ECDSA, where Verify is slower than Key Gen plus Sign: 1 x Key Gen, 2 x Secret Gen and 2 x Verify.

The table below is a restating of the TLS 1.3 handshake including processing of message and the major cryptographic operations.

From this we can see that a TLS 1.3 handshake with RSA, where Verify is a lot faster than Sign, is dependent on: 2 x Key Gen, 1 x Secret Gen, 1 x Sign. Therefore, a Secret Gen and Verify in TLS 1.2 are saved. For ECDSA, where Verify is a lot slower than Sign, the TLS 1.3 handshake is dependent on: 2 x Key Gen, 1 x Secret Gen, 2 x Verify. Therefore, a Secret Gen in TLS 1.2 is traded for a faster Key Gen.

Running both the client and server on the same computer results in about a 15% improvement in the performance of ephemeral DH with RSA handshakes – mostly due to the parallel operations. With ephemeral ECDH and RSA there is about a 6% improvement, and with ECDHE and ECDSA there is about a 7% improvement – mostly due to the saving in round-trips.

These improvements come for free when using TLS 1.3 without the HelloRetryRequest. The next blog will discuss handshakes using pre-shared keys.

For more information regarding wolfSSL and the TLS 1.3 full handshake, please contact facts@wolfssl.com.

wolfSSL at NXP Tech Days Minneapolis

wolfSSL is at wolfSSL at NXP Tech Days Minneapolis this year! NXP Technology Days is a deep-dive, technical training program for engineers designing solutions with embedded technology. This one-day event offers hands-on workshops and technical lectures over multiple markets enabling attendees to customize a schedule that is most relevant to their training needs.

Where wolfSSL will be located for this Tech Days:
Venue: Doubletree by Hilton Minneapolis Park Place
When: April 16, 2019
Directions: https://doubletree3.hilton.com/en/hotels/minnesota/doubletree-by-hilton-hotel-minneapolis-park-place-MSPPHDT/maps-directions/index.html

Stop by to hear more about the wolfSSL embedded SSL/TLS library, the wolfCrypt encryption engine, to meet the wolfSSL team, or to get some free stickers and swag!

For more information about wolfSSL, its products, or future events, please contact facts@wolfssl.com.

More information about NXP Tech Days can be found here: https://www.nxp.com/support/training-events/nxp-technology-days:NXP-TECH-DAYS

TLS 1.3 Performance Analysis – Resumption

TLS 1.3 is the latest version of the SSL/TLS specification. There are significant changes to messages and the message flow. These changes are targeted at security and performance.

The first performance difference to note is a degradation. In TLS 1.2 performing a resumption handshake is very quick. This comes at a security cost though. Each time a client resumes a session, the same session ID is used and the same master secret is used. Therefore, if the master secret is compromised then all resumed sessions are revealed. Also, TLS 1.2 resumption is stateful and can have performance issues in a multi-server architecture.

TLS 1.3 only uses session tickets to resume a session. This mechanism has the client send an opaque session ticket to the server that contains a server encrypted version of all the information required to resume the session. Once again the same master secret is used across handshakes but the default behavior is to perform a key exchange. A unique, shared secret is generated and combined with the master secret when calculating keys and IVs. This mechanism then provides forward secrecy.

The performance trade-off here is that using a session ticket requires decryption of the session ticket. Also, TLS 1.3 performs more encryption/decryption and hashing operations in the handshake anyway. Therefore, when running a client and server on the same computer, a TLS 1.3 handshake is more than 20% slower. On a high latency network, these will not be noticeable as symmetric cipher and digest algorithms are the fastest of operations.

But also consider the default behaviour that results in a key exchange. DH key and secret generation are some of the most expensive operations and the handshake, again running both client and server on the same computer, using 2048-bit DH parameters can take 13 times as long as TLS 1.2 resumption. ECDH can be used instead and is at least twice as slow when using a highly optimised implementation.

There is no way in TLS 1.3 to avoid this performance degradation and resumption has the fastest handshake performance. Using optimised ECDH will give you the best performance and better security. There is a way to improve the resumption performance, in some cases, which will be discussed in a future blog in this series.

For more information about wolfSSL and TLS 1.3 session ticket resumption, please contact facts@wolfssl.com.

wolfSSL and the Selfie Attack

People have been asking if wolfSSL is vulnerable to the ’Selfie’ attack (https://eprint.iacr.org/2019/347).  We are glad to say that we follow all the recommendations made by the authors.  First, though, an explanation of the attack.

Overview

The attack targets the use of Pre-Shared Keys (PSKs) with TLS 1.3 though TLS 1.2 is also vulnerable.  There are very specific use cases that are affected. When a group of computers want to connect to each other then sharing a PSK is a simple way to set things up. Membership of the group is based on the knowledge of the PSK.  This means that certificate authentication is not used.

Attack

The attack scenario is when a new computer comes into the network that can intercept or Man-in-the-Middle (MitM) the communications between computers.  When a computer, let’s call it Alice, acting as a client sends a TLS ClientHello, the MitM, which we’ll call Eve, reflects the message back in a new connection to Alice.  Alice acting as a server sees a new TLS ClientHello and in parallel responds with the first round of messages. These messages are sent back by Eve to the client on Alice. Alice as a client uses the messages to establish a connection and sends a response.  Eve uses the response to respond to Alice the server and so on and a secure connection is established.

Because everyone is using the same PSK for client and server connections, Alice does not notice anything wrong!  Now that a secure connection has been established, which Eve cannot decrypt, it can be hard to see what the issue would be.  The attack comes when a message like ‘Delete your copy of this file, I have a copy’ is sent. Eve reflects the message back and Alice decides that the she doesn’t have to keep a copy after all and deletes it.

The paper lists a number of scenarios that may be vulnerable:

  • Content Delivery Networks (CDNs) - poisoning caches.
  • P2P Networks.
  • WiFi networks that rely on PSKs for the entire network.
  • Leader-election and consensus protocols.

Mitigations and Recommendations

One way to prevent this attack is to use the Server Name indicator (SNI) extension. This way Alice recognises she didn’t connect to the computer she wanted to but to herself.

The recommendations of the paper are:

  • Don’t share PSKs amongst a group of computers unless certificates are used initially to establish identity. This goes against the PSK use case!
  • If you must use a shared PSK without certificates, then use the SNI extension.
  • TLS toolkits should either not implement PSK or not have it configured by default.

By default in wolfSSL, PSKs are not enabled but are available for use when you need it.  wolfSSL also implements the SNI extension and we encourage you to use it.

For more information about the wolfSSL library, please contact facts@wolfssl.com.

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