computer science

Mod ssl

Mod ssl 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 Mod ssl rather than just read about it. In short: mod_ssl is an optional module for the Apache HTTP Server. It provides strong cryptography for the Apache v1.3 and v2 webserver via the Secure Sockets Layer (SSL v2/v3) and Transport Layer Security (TLS v1) cryptographic protocols by the help of the Open Source SSL/TLS toolkit OpenSSL.

Key takeaways

Mod ssl 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 Mod ssl to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mod ssl from memory before moving on to harder problems.

Reference excerpt

mod_ssl is an optional module for the Apache HTTP Server. It provides strong cryptography for the Apache v1.3 and v2 webserver via the Secure Sockets Layer (SSL v2/v3) and Transport Layer Security (TLS v1) cryptographic protocols by the help of the Open Source SSL/TLS toolkit OpenSSL.

History The mod_ssl v1 package was initially created in April 1998 by Ralf S. Engelschall via porting Ben Laurie's Apache-SSL 1.17 source patches for Apache 1.2.6 to Apache 1.3b6. Because of conflicts with Ben Laurie's development cycle it then was re-assembled from scratch for Apache 1.3.0 by merging the old mod_ssl 1.x with the newer Apache-SSL 1.18. From this point on mod_ssl lived its own life as mod_ssl v2. The first publicly released version was mod_ssl 2.0.0 from August 10, 1998. After US export restrictions on cryptographic software were loosened, mod_ssl became part of the Apache HTTP Server with the release of Apache httpd 2. As of October 10, 2009, the latest version released for mod_ssl in Apache 1.3 is mod_ssl v2.8.31-1.3.41 on February 8, 2008.

Overview The original version created for Apache v1.3 was initially created in April 1998 by Ralf S. Engelschall via porting Ben Laurie's Apache-SSL 1.17 source patches for Apache 1.2.6 to Apache 1.3b6. This version is under a BSD-style license. The version for v2.0 and later, in contrast, is maintained by Apache Software Foundation and licensed under Apache License 2.0. It is possible to provide HTTP and HTTPS with a single server machine, because HTTP and HTTPS use different server ports, so there is no direct conflict between them. It is either the maintainer who would run two separate Apache server instances (one binds to port 80, the other to port 443) or use Apache's virtual hosting facility where the maintainer can create two virtual servers which Apache dispatches: one responding to port 80 and speaking HTTP and one responding to port 443 speaking HTTPS.

Differences The original mod_ssl in Apache 1.3 available at www.modssl.org is a third-party add-on package requiring additional steps in the compilation and configuration process. Also, the maintainer of the server needs to resolve additional system and Apache dependencies. Apache 2, in contrast, is a built-in module maintained by Apache Software Foundation, and mod_ssl can be easily activated in the compilation and configuration options.

Worked examples

Example 1 — a first encounter with Mod ssl

Start with the simplest possible case. Write down what Mod ssl 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 Mod ssl 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 Mod ssl 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 Mod ssl

In research: Mod ssl 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 Mod ssl 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: Mod ssl is common in secondary-school and first-year university syllabi. It links to neighbouring topics Apache httpd modules, Transport Layer Security, Web server software, so understanding it makes those chapters shorter.
In everyday life: Look for Mod ssl 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 Mod ssl in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mod ssl 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 Mod ssl out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mod ssl in simple terms?

Why does Mod ssl 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 Mod ssl?

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 Mod ssl.