388 lines
12 KiB
HTML
388 lines
12 KiB
HTML
<!DOCTYPE html>
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
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<head>
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<meta charset="utf-8" />
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<title>Cryptography</title>
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</head>
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<body>
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<main>
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<article>
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<h1>Cryptography</h1>
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<address class="h-card">
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by
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<a rel="author" class="u-url" href="http://changelog.ca/"><span class="p-given-name">Charles</span> <span class="p-additional-name">Iliya</span> <span class="p-family-name">Krempeaux</span></a>
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</address>
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<p>
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<strong>Cryptography</strong> is about how to communicate securely — and how to do so even when there is a <em>malicious</em> person, people, organization(s), or other entities who are trying to stop you from doing so.
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</p>
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<p>
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<strong>Cryptography</strong> is an important part of <strong>privacy</strong>.
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</p>
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<p>
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<strong>Cryptography</strong> is also sometimes called <strong>cryptology</strong>.
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</p>
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<section>
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<h2>Goals</h2>
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<p>
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<strong>Cryptography</strong> is generally used to try provide three different but related things:
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</p>
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<ul>
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<li><strong>confidentiality</strong>,</li>
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<li><strong>integrity</strong>, and</li>
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<li><strong>authenticity</strong>.</li>
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</ul>
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<p>
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These three goals form the foundation of the security that <strong>cryptography</strong> tries to provide.
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</p>
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</section>
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<dl>
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<dt>Confidentiality</dt>
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<dd>
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<p>
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<strong>Confidentiality</strong> is the goal that only the person, people, organization(s), or other entities you addressed the message to can read the message.
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</p>
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<p>
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<strong>Confidentiality</strong> is about how to hide information so that only the whomever or whatever you want to read, listen to, or watch, etc a message can do so.
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</p>
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<p>
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(In <strong>cryptography</strong>, things such as text, audio, and video all get called a "<strong>message</strong>".)
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</p>
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<p>
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For example, if I record a video on my mobile phone and send it to my wife, <strong>confidentiality</strong> has it so that only my wife can watch the video, and no one else.
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Not even the people and organizations that provide the communication infrastructure that I use to send the video to my wife.
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</p>
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<p>
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<strong>Confidentiality</strong> is important for <strong>privacy</strong>.
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</p>
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</dd>
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<dt>Integrity</dt>
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<dd>
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<p>
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<strong>Integrity</strong> is the goal that a message’s contents cannot be tampered with.
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</p>
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<p>
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For example, if I write this message to my wife —
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</p>
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<blockquote>
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<p>
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Meet me at park by the kids' school at 3pm.
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</p>
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</blockquote>
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<p>
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— <strong>integrity</strong>, for example, has it so someone else cannot change my message to:
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</p>
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<blockquote>
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<p>
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Meet me at in the dark scary alley behind the grocery store at 2pm.
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</p>
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</blockquote>
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<p>
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With <strong>integrity</strong>, the message my wife receives will be exactly what I sent her.
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</p>
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</dd>
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<dt>Authenticity</dt>
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<dd>
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<p>
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<strong>Authenticity</strong> is the goal that if someone or something claims to be who someone or something, then you can tell if it is actually them.
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</p>
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<p>
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This could be with someone logging into a system.
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Or it could be with <em>who</em> or <em>what</em> a message is claimed to be from.
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</p>
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<p>
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For example, if my wife receives a message, she can tell if the message is actually from me or not.
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</p>
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</dd>
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</dl>
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<section>
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<h2>Jargon</h2>
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<p>
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Like many specialties, <strong>cryptography</strong> has its own <em>jargon</em>
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—
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special words and special phrases that have special meanings in the specialty.
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</p>
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<p>
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Sometimes <em>jargon</em> is comprised of new words and new phrases.
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But sometimes <em>jargon</em> is comprised of existing words and existing phrases, which are given new meanings!
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(This latter form of <em>jargon</em> can not only confuse, but also mislead people who don't understand the <em>jargon</em> of the specialty.)
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</p>
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<p>
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Some of the basic <em>jargon</em>, in <strong>cryptography</strong>, includes the following words in phrases:
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<em>cipher</em>,
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<em>cipher-text</em>,
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<em>decrypt</em>,
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<em>decryption</em>,
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<em>digest</em>,
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<em>encrypt</em>,
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<em>encryption</em>,
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<em>hash</em>,
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<em>message</em>,
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<em>party</em>, and
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<em>plain-text</em>.
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</p>
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<p>
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Some of the more advanced <em>jargon</em>, in <strong>cryptography</strong>, includes the following words in phrases:
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<em>avalanche-effect</em>,
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<em>bcrypt</em>,
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<em>brute-force-attack</em>,
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<em>collision-attack</em>,
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<em>decryption algorithm</em>,
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<em>Ed25519</em>,
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<em>EdDSA</em>,
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<em>encryption algorithm</em>,
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<em>GPG</em>,
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<em>finger-print</em>,
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<em>key</em>,
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<em>MD5</em>,
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<em>pass-phrase</em>,
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<em>pass-word</em>,
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<em>pepper</em>,
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<em>PGP</em>,
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<em>proof-of-work</em>,
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<em>rainbow-table</em>,
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<em>ROT-13</em>,
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<em>RSA</em>,
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<em>running key cipher</em>,
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<em>salt</em>,
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<em>scrypt</em>,
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<em>scytale</em>,
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<em>SHA-1</em>,
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<em>SHA-2</em>,
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<em>SHA-3</em>,
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<em>shift-cipher</em>,
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<em>sponge-function</em>,
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<em>signature</em>,
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<em>substitution cipher</em>,
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<em>TLS</em>,
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<em>transposition cipher</em>,
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<em>web-of-trust</em>,
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etc etc etc.
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(There are a lot more advanced <em>jargon</em> than what we listed.)
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</p>
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<p>
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Learning <strong>cryptography</strong>'s <em>jargon</em> will help you understand <strong>cryptography</strong>
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—
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as specialists in <strong>cryptography</strong> will very very likely be using <strong>cryptography</strong>'s <em>jargon</em>.
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</p>
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<p>
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Let's first focus on defining the <strong>basic</strong> <em>jargon</em> in <strong>cryptography</strong>.
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</p>
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<p>
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(These definitions <em>won't</em> be in alphabetical order.
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But instead will be in an order that I think will make them easier to understand.
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Some <em>jargon</em> is easier to understand once you understand other <em>jargon</em>.)
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</p>
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<section>
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<h3>Plain-Text, Cipher-Text, Encryption, Decryption</h3>
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<p>
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What <strong>plain-text</strong> and <strong>cipher-text</strong> as well as <strong>encryption</strong> and <strong>decryption</strong> are is probably most easily understood with some examples.
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</p>
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<section>
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<h4>Example №1</h4>
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<p>
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If I write this message to my wife —
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</p>
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<blockquote>
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<p>
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COULD YOU PICK UP THE KIDS FROM SCHOOL TODAY AT 2PM, PLEASE?
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</p>
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</blockquote>
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<p>
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— that is <strong>plain-text</strong>.
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</p>
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<p>
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I might <em>not</em> want anyone else to be able to read that message (other than my wife).
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So I can hide that message from others by turning that <strong>plain-text</strong> message into a <strong>cipher-text</strong> message to try to accomplish that.
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</p>
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<p>
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The process of turning a <strong>plain-text</strong> message into a <strong>cipher-text</strong> message is called <strong>encryption</strong>.
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</p>
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<p>
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What would a <strong>cipher-text</strong> message for that <strong>plain-text</strong> message look like‽
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—
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well, it depends on what <strong>encryption algorithm</strong> we use.
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</p>
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<p>
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For a very very simple example, if we were using the <strong>ROT-13</strong> <em>encryption algorithm</em>, then the <strong>cipher-text</strong> would be:
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</p>
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<blockquote>
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<p>
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PBHYQ LBH CVPX HC GUR XVQF SEBZ FPUBBY GBQNL NG 2CZ, CYRNFR?
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</p>
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</blockquote>
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<p>
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(We will look closer at <strong>ROT-13</strong> later.)
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</p>
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<p>
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For my wife to read my message, she would have to turn that <strong>cipher-text</strong> back into <strong>plain-text</strong>.
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</p>
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<p>
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The process of turning a <strong>cipher-text</strong> message into a <strong>plain-text</strong> message is called <strong>decryption</strong>.
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</p>
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</section>
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<section>
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<h4>Example №2</h4>
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<p>
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Let's look at another example.
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We will use the same <strong>plain-text</strong> —
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</p>
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<p>
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I.e. again I will write this message to my wife —
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</p>
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<blockquote>
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<p>
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COULD YOU PICK UP THE KIDS FROM SCHOOL TODAY AT 2PM, PLEASE?
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</p>
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</blockquote>
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<p>
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— and again that will be the <strong>plain-text</strong>.
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</p>
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<p>
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And again, I will <em>not</em> want anyone else to be able to read that message (other than my wife).
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So I will hide that message from others by turning that <strong>plain-text</strong> message into a <strong>cipher-text</strong> message to try to accomplish that.
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</p>
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<p>
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<strong>But this time we will use a different <em>encryption algorithm</em>.</strong>
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</p>
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<p>
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With this example, we will use another very very simple <em>encryption algorithm</em> — we will use a <strong>substitution cipher</strong>.
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To use a <strong>substitution cipher</strong> as your <em>encryption algorithm</em> you need to pick a <em>substitution-alphabet</em>.
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The <em>substitution-alphabet</em> we will use is —
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</p>
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<table>
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<tr>
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<th scope="row">normal English alphabet</th>
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<td>A</td>
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<td>B</td>
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<td>C</td>
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<td>D</td>
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<td>E</td>
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<td>F</td>
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<td>G</td>
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<td>H</td>
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<td>I</td>
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<td>J</td>
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<td>K</td>
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<td>L</td>
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<td>M</td>
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<td>N</td>
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<td>O</td>
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<td>P</td>
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<td>Q</td>
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<td>R</td>
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<td>S</td>
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<td>T</td>
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<td>U</td>
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<td>V</td>
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<td>W</td>
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<td>X</td>
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<td>Y</td>
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<td>Z</td>
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</tr>
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<tr>
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<th scope="row">cipher alphabet</th>
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<td>Q</td>
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<td>K</td>
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<td>T</td>
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<td>N</td>
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<td>H</td>
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<td>F</td>
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<td>P</td>
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<td>R</td>
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<td>M</td>
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<td>S</td>
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<td>U</td>
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<td>J</td>
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<td>W</td>
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<td>C</td>
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<td>B</td>
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<td>D</td>
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<td>Z</td>
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<td>G</td>
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<td>X</td>
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<td>I</td>
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<td>V</td>
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<td>Y</td>
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<td>O</td>
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<td>E</td>
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<td>A</td>
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<td>L</td>
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</tr>
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</table>
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<p>
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(We will look closer at <strong>substitution ciphers</strong> later.
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Don't worry if, for example, what a <em>substitution-alphabet</em> is doesn't make sense yet.)
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</p>
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<p>
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With this, if we <strong>encrypt</strong> our <strong>plain-text</strong>, our <strong>cipher-text</strong> would be:
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</p>
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<blockquote>
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<p>
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TBVJN ABV DMTU VD IRH UMNX FGBW XTRBBJ IBNQA QI 2DW, DJHQXH?
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</p>
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</blockquote>
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<p>
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And again, for my wife to be able to read my message, she would need to have to <strong>decrypt</strong> the <strong>cipher-text</strong> back into the <strong>plain-text</strong> to get:
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</p>
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<blockquote>
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<p>
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COULD YOU PICK UP THE KIDS FROM SCHOOL TODAY AT 2PM, PLEASE?
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</p>
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</blockquote>
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</section>
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</section>
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<p>
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So, now that you have seen those examples, let's define those terms.
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</p>
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<dl>
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<dt>Plain-Text</dt>
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<dd>
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<p>
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<strong>Plain-Text</strong> is the original message.
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</p>
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<p>
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In <strong>cryptography</strong>, text, audio, and video all get called a "<strong>plain-text</strong>".
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Which can be a bit confusing and even misleading as, in regular language, the word "<em>text</em>" tends not to include <em>audio</em> and <em>video</em>.
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But in <strong>cryptography</strong> it does.
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</p>
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<p>
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Usually when <strong>cryptography</strong> specialists talk about <strong>plain-text</strong>, they are doing so in relation to <strong>cipher-text</strong>.
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</p>
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</dd>
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<dt>Cipher-Text</dt>
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<dd>
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<p>
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To make a <strong>plain-text</strong> message <strong>confidential</strong>, we turn it into a <strong>cipher-text</strong>.
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</p>
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<p>
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We turn a <strong>plain-text</strong> message into a <strong>cipher-text</strong> message to hide the message so that only the person, etc you want to read, listen to, or watch, etc the message can do so.
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</p>
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</dd>
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<dt>Encryption</dt>
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<dd>
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<p>
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<strong>Encryption</strong> is the process of turning <strong>plain-text</strong> into a <strong>cipher-text</strong>.
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</p>
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<p>
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What the <strong>cipher-text</strong> ends up being depends on what <strong>encryption algorithm</strong> you end up using.
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</p>
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</dd>
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<dt>Decryption</dt>
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<dd>
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<p>
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<strong>Decryption</strong> is the process of turning <strong>cipher-text</strong> back into <strong>plain-text</strong>.
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</p>
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</dd>
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</dl>
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</section>
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</article>
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</main>
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</body>
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</html>
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