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| <h2 class="chapter">32 DES Encryption and Password Handling</h2> |
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| <!-- %MENU% DES encryption and password handling --> |
| <p>On many systems, it is unnecessary to have any kind of user |
| authentication; for instance, a workstation which is not connected to a |
| network probably does not need any user authentication, because to use |
| the machine an intruder must have physical access. |
| |
| <p>Sometimes, however, it is necessary to be sure that a user is authorized |
| to use some service a machine provides—for instance, to log in as a |
| particular user id (see <a href="Users-and-Groups.html#Users-and-Groups">Users and Groups</a>). One traditional way of |
| doing this is for each user to choose a secret <dfn>password</dfn>; then, the |
| system can ask someone claiming to be a user what the user's password |
| is, and if the person gives the correct password then the system can |
| grant the appropriate privileges. |
| |
| <p>If all the passwords are just stored in a file somewhere, then this file |
| has to be very carefully protected. To avoid this, passwords are run |
| through a <dfn>one-way function</dfn>, a function which makes it difficult to |
| work out what its input was by looking at its output, before storing in |
| the file. |
| |
| <p>The GNU C library provides a one-way function that is compatible with |
| the behavior of the <code>crypt</code> function introduced in FreeBSD 2.0. |
| It supports two one-way algorithms: one based on the MD5 |
| message-digest algorithm that is compatible with modern BSD systems, |
| and the other based on the Data Encryption Standard (DES) that is |
| compatible with Unix systems. |
| |
| <p>It also provides support for Secure RPC, and some library functions that |
| can be used to perform normal DES encryption. |
| |
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| <li><a accesskey="1" href="Legal-Problems.html#Legal-Problems">Legal Problems</a>: This software can get you locked up, or worse. |
| <li><a accesskey="2" href="getpass.html#getpass">getpass</a>: Prompting the user for a password. |
| <li><a accesskey="3" href="crypt.html#crypt">crypt</a>: A one-way function for passwords. |
| <li><a accesskey="4" href="DES-Encryption.html#DES-Encryption">DES Encryption</a>: Routines for DES encryption. |
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