computer science

OpenSSL

OpenSSL is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand OpenSSL rather than just read about it. In short: OpenSSL is a software library for applications that provide secure communications over computer networks against eavesdropping, and identify the party at the other end. It is widely used by Internet servers, including the majority of HTTPS websites.

Key takeaways

OpenSSL belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect OpenSSL to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of OpenSSL from memory before moving on to harder problems.

Reference excerpt

OpenSSL is a software library for applications that provide secure communications over computer networks against eavesdropping, and identify the party at the other end. It is widely used by Internet servers, including the majority of HTTPS websites. OpenSSL contains an open-source implementation of the SSL and TLS protocols. The core library, written in the C programming language, implements basic cryptographic functions and provides various utility functions. Wrappers allowing the use of the OpenSSL library in a variety of computer languages are available. The OpenSSL Software Foundation (OSF) represents the OpenSSL project in most legal capacities including contributor license agreements, managing donations, and so on. OpenSSL Software Services (OSS) also represents the OpenSSL project for support contracts. OpenSSL is available for most Unix-like operating systems (including Linux, macOS, and BSD), Microsoft Windows and OpenVMS.

Project history The OpenSSL project was founded in 1998 to provide a free set of encryption tools for the code used on the Internet. It is based on a fork of SSLeay by Eric Andrew Young and Tim Hudson, which unofficially ended development on December 17, 1998, when Young and Hudson both went to work for RSA Security. The initial founding members were Mark Cox, Ralf Engelschall, Stephen Henson, Ben Laurie, and Paul Sutton. In 2018 OpenSSL version numbering skipped from 1.1.1 to 3.0.0, omitting 2 as a major version number to avoid a conflict with one of OpenSSL's modules. Version 3.0.0 was the first to use the Apache License. As of May 2019, the OpenSSL management committee consisted of seven people and there are seventeen developers with commit access (many of whom are also part of the OpenSSL management committee). There were only two full-time employees (fellows) and the remainder were volunteers. By 2024, there were fourteen employees. The project had a total income of US$5.5 million in 2024. Development of TLS 1.3 was sponsored by Akamai.

Major version releases

Algorithms OpenSSL supports a number of different cryptographic algorithms:

Ciphers

AES, Blowfish, Camellia, ChaCha20, Poly1305, SEED, CAST-128, DES, IDEA, RC2, RC4, RC5, Triple DES, GOST 28147-89, SM4 Cryptographic hash functions

MD5, MD4, MD2, SHA-1, SHA-2, SHA-3, RIPEMD-160, MDC-2, GOST R 34.11-94, BLAKE2, Whirlpool, SM3 Public-key cryptography

RSA, DSA, Diffie–Hellman key exchange, Elliptic curve, X25519, Ed25519, X448, Ed448, GOST R 34.10-2001, SM2 (Perfect forward secrecy is supported using elliptic-curve Diffie–Hellman since version 1.0.)

FIPS 140 validation FIPS 140 is a U.S. Federal program for the testing and certification of cryptographic modules. An early FIPS 140-1 certificate for OpenSSL's FOM 1.0 was revoked in July 2006 "when questions were raised about the validated module's interaction with outside software." The module was re-certified in February 2007 before giving way to FIPS 140-2. OpenSSL 1.0.2 supported the use of the OpenSSL FIPS Object Module (FOM), which was built to deliver FIPS approved algorithms in a FIPS 140-2 validated environment. OpenSSL controversially decided to categorize the 1.0.2 architecture as 'end of life' or 'EOL', effective December 31, 2019, despite objections that it was the only version of OpenSSL that was currently available with support for FIPS mode. As a result of the EOL, many users were unable to properly deploy the FOM 2.0 and fell out of compliance because they did not secure extended support for the 1.0.2 architecture, although the FOM itself remained validated for eight months further. The FIPS Object Module 2.0 remained FIPS 140-2 validated in several formats until September 1, 2020, when NIST deprecated the usage of FIPS 186-2 for Digital Signature Standard and designated all non-compliant modules as 'Historical'. This designation includes a caution to federal agencies that they should not include the module in any new procurements. All three of the OpenSSL validations were included in the deprecation – the OpenSSL FIPS Object Module (certificate #1747), OpenSSL FIPS Object Module SE (certificate #2398), and OpenSSL FIPS Object Module RE (certificate #2473). Many 'private label' OpenSSL-based validations and clones created by consultants were also moved to the Historical List, although some FIPS validated modules with replacement compatibility avoided the deprecation, such as BoringCrypto from Google and CryptoComply from SafeLogic. The OpenSSL Management Committee announced a change in the versioning scheme. Due to this change, the major number of the next major version would have been doubled, since the OpenSSL FIPS module already occupied this number. Therefore, the decision was made to skip the OpenSSL 2.0 version number and continue with OpenSSL 3.0 . OpenSSL 3.0 restored FIPS mode and underwent FIPS 140-2 testing, but with significant delays: The effort was first kicked off in 2016 with support from SafeLogic and further support from Oracle in 2017, but the process has been challenging. On October 20, 2020, the OpenSSL FIPS Provider 3.0 was added to the CMVP Implementation Under Test List, which reflected an official engagement with a testing lab to proceed with a FIPS 140-2 validation. This resulted in a slew of certifications in the following months.

… excerpt ends here. Continue reading the full article.

Illustrations

A logo representing the Heartbleed bug

Worked examples

Example 1 — a first encounter with OpenSSL

Start with the simplest possible case. Write down what OpenSSL claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to OpenSSL before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about OpenSSL ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of OpenSSL

In research: OpenSSL appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses OpenSSL in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: OpenSSL is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1998 software, C (programming language) libraries, Cryptographic software, so understanding it makes those chapters shorter.
In everyday life: Look for OpenSSL outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study OpenSSL in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what OpenSSL means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain OpenSSL out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is OpenSSL in simple terms?

Why does OpenSSL matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study OpenSSL?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on OpenSSL.