Abstract:
The open source encryption software library OpenSSL officially released version 4.1 on October 23, 2026. This update introduces a number of new features and performance optimizations, including support for the DTLS 1.3 protocol, implementation of the GREASE mechanism, accelerated post-quantum cryptographic algorithms, and optimization of some encryption operations for x86-64 processors that support the AVX-512 instruction set. In addition, the new version also removes build support for Windows CE and Windows Itanium platforms to further clean up historical legacy code.
OpenSSL is one of the most important encryption software libraries in the Internet infrastructure and is widely used in HTTPS websites, servers, VPNs, applications, and other systems that require secure communication. It is responsible for handling tasks such as TLS connections, digital certificates, key exchange, encryption, and data integrity verification, so its updates are not only relevant to developers, but also affect a large number of software and network services that rely on it.
One of the most important new features of this update is the official support for DTLS 1.3. DTLS, the Datagram Transport Layer Security Protocol, can be understood as a security protocol oriented to datagram communication. Its design goals are similar to TLS, but it can adapt to data transmission environments such as UDP where packet loss, out-of-order or delayed arrival may occur.
Traditional TLS is mainly used for TCP connections, while many real-time communications, online games, voice and video applications, and some IoT devices require the use of UDP to reduce transmission delays. DTLS can provide encryption, authentication and data integrity protection in these scenarios. DTLS 1.3 further improves the protocol design, shortens the handshake process, and introduces security improvements corresponding to modern TLS technology.
The new version also adds DTLS support to the SSL listener API, making it easier for developers to use OpenSSL to build security services based on the datagram protocol. For applications that require low-latency communication, this is expected to reduce the workload of implementing relevant security mechanisms themselves.
However, DTLS 1.3 does not mean that all applications using OpenSSL will automatically receive performance improvements. The application still needs to actively use the corresponding interface and be configured and tested according to the actual network environment. The benefits of new protocols also depend on communication patterns, network packet loss rates, and implementation on both the client and server sides.
OpenSSL 4.1 also adds support for the GREASE mechanism. GREASE is the abbreviation of "Generate Random Extensions And Sustain Extensibility", which was originally standardized by the Internet Engineering Task Force to improve the extension compatibility of the TLS protocol.
The core approach of GREASE is to send some randomized protocol values that are specially reserved and have no actual function during the TLS handshake process. This allows you to test whether communicating parties are able to correctly handle unknown extension fields and parameters, rather than mistakenly assuming that all future protocol values have been defined in advance. By proactively exposing such compatibility issues, developers can reduce the risk of connection failures when adding new protocol features in the future.
In terms of cryptographic performance, OpenSSL 4.1 continues to enhance the implementation of post-quantum cryptographic algorithms. With the development of quantum computing technology, traditional public key cryptography systems are facing potential security challenges in the future, and post-quantum cryptography algorithms are gradually entering the stage of standardization and actual deployment. OpenSSL focuses on optimizing ML-DSA and ML-KEM related operations this time.
ML-DSA is a post-quantum digital signature algorithm that can be used to verify identity and prevent data from being tampered with; ML-KEM is a post-quantum key encapsulation mechanism used to negotiate or establish shared keys required for secure communication. Both are based on the post-quantum cryptography system promoted by the National Institute of Standards and Technology.
The new version optimizes the number theory transformation (NTT) operation of ML-DSA and ML-KEM for processor architectures such as PPC64LE, and also improves the implementation of ML-DSA on the x86-64 platform. Number theory transformation is an important calculation link in this type of lattice-based cryptographic algorithm, and optimizing its execution efficiency can reduce the computational overhead of some encryption operations.
For x86-64 processors that support the AVX-512 instruction set, the new version also adds SHAKE x4 optimization for ML-DSA. SHAKE is a scalable output function that can generate output of different lengths as needed and plays an important role in modern cryptographic algorithms. By taking advantage of the vectorized computing power provided by AVX-512, OpenSSL can process more data in parallel, thereby improving the throughput of related operations.
AES encryption has also been optimized. OpenSSL 4.1 improves the AES-CBC decryption implementation for the x86-64 platform, and combines instruction set capabilities such as AVX-512 and VAES to improve processing efficiency. Actual acceleration will be affected by CPU model, compilation options and specific workloads, and not all processors will achieve the same benefits.
In addition to the mainstream x86-64 and PPC64LE platforms, the new version also adds preliminary support for the Russian Elbrus 2000 (E2K) processor architecture for the first time. This means that OpenSSL is further expanding the hardware platforms on which it can run. However, preliminary architecture support does not mean that all algorithms, optimization paths and peripheral tools have full production environment support.
This update also involves the IKEv2 Key Derivation Function (KDF). IKEv2 is widely used in Internet key exchange protocols and is commonly used in network security scenarios such as IPsec VPN. The new support can expand the cryptographic functions of OpenSSL and provide a more direct implementation path for developers who need to use this key derivation mechanism.
In terms of compatibility, OpenSSL 4.1 officially removes the build targets for Windows CE and Windows Itanium processor platforms. Windows CE is an early operating system for embedded devices, and Itanium is the IA-64 processor architecture that Intel once developed. As these platforms gradually fall out of mainstream use, the value of continuing to maintain related build targets decreases, and removing them can reduce the maintenance burden of the project.
In terms of configuration options, OpenSSL has deleted the no-ecdsa and no-ecdh options. The development team pointed out that these two options did not actually disable the corresponding implementation before, so it was easy to cause misunderstandings. Developers who need to disable elliptic curve cryptography functionality should now use the no-ec configuration option.
Another notable change involves the tsget tool. This tool previously relied on the Perl module WWW::Curl::Easy, which has been discontinued. It now uses Net::Curl::Easy instead. For users who rely on tsget, they need to confirm that the new dependencies have been installed before upgrading, otherwise related functions may not function properly.
Although OpenSSL 4.1 brings a number of new features, the release notes also list known issues related to DTLS. For example, after receiving the KeyUpdate message of DTLS 1.3, some post-handshake records that have not yet been confirmed may not be resent as expected; problems may also occur with the handshake under certain packet loss conditions. The development team has plans to fix these defects in subsequent releases.
Therefore, for enterprises and developers running critical network services, they should still read the official release notes carefully and verify DTLS-related functions in the test environment before upgrading. If the application does not use new features, the upgrade time should be determined based on its own dependencies, the maintenance strategy of the operating system release, and the security requirements. It is not necessary to immediately replace the encryption library in the production environment just because the version number changes.
Overall, OpenSSL 4.1 is a functional version with new protocol support, post-quantum cryptography performance optimization and platform maintenance adjustments as its core. DTLS 1.3 and GREASE will help developers build more modern secure communication systems, while AVX-512 and other architectural optimizations further improve the efficiency of some cryptographic operations. As post-quantum cryptography gradually enters the actual deployment stage, the continuous updating of basic software libraries such as OpenSSL will become an important part of the evolution of the Internet security system.
Learn more:
https://github.com/openssl/openssl/releases/tag/openssl-4.1.0
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