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Tech Note #35: How Encryption and Digital Signatures Work
1999 Bionic Buffalo Corporation; All Rights Reserved.
                  19 May 1999
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Bionic Buffalo Tech Note #35:
How Encryption and Digital Signatures Work
last revised Wednesday 19 May 1999
©1999 Bionic Buffalo Corporation. All rights reserved.
Tatanka and TOAD are trademarks of Bionic Buffalo Corporation.
This is a very basic introduction to encryption and digital signatures. It explains how they work
and gives some examples of how they are used.
Encryption scrambles or modifies a message or document so it cannot be read and understood,
except by the intended recipient. A key is necessary to reverse the scrambling or modification,
to make the message readable. Encryption is used for secrecy in communication.
Digital signatures are used to verify that a message or document was authored by a certain
person, and that it was not altered or modified by anyone else. (The process of verifying the
integrity of a document is authentication.)
Encryption and digital signatures can be used together, or separately.
a message may be encrypted, but not digitally signed (only people with the key can read it,
but the reader cannot be certain who actually wrote it)
a message may be digitally signed, but not encrypted (everyone can tell who wrote it, and
everyone can read it)
a message may be encrypted first, then digitally signed (only someone with the key can read
it, but anyone can tell who wrote it)
a message may be digitally signed first, then encrypted (only someone with the key can read
it, and only that same reader can be sure who sent the document)
These technologies are used nearly everywhere. They are used to safeguard network traffic
among different computers, to keep e-mail private, to conduct electronic commerce, to control
access to buildings and files, and to prevent playing television channels by unauthorized users.
Types of Encryption
Encryption depends on modifying or scrambling messages so a key is necessary to understand
the message. As an example, suppose we take a message and change each letter of the alphabet
by substituting a later letter.