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ing log entries. It is possible, however, to sign and/or encrypt the entries before submitting<br />

them to the logging server.<br />

On Unix systems that use syslog, there is no guarantee that entries will be written to<br />

log files in the order in which they are submitted by a program. This is a side effect of<br />

using datagram sockets for communication between clients and the server. With this<br />

in mind, make sure that you include all of the information required to decrypt or verify<br />

the signature on a log entry in a single entry. Note also that other clients could<br />

possibly make log entries in between multiple entries being made from your program,<br />

which is something that can also happen with the Windows logging service.<br />

Signing and encrypting log entries will prevent an attacker from modifying the log<br />

entries undetected, but it will not prevent an attacker from deleting the log entries or<br />

replacing them with garbage or captured log entries. There is no way to really prevent<br />

an attacker from deleting the contents of a log file or making the contents<br />

unreadable. The best you can do is to set things up in such a way that you can determine<br />

when log files have been manipulated, but signing and encrypting alone will<br />

not do this for you.<br />

To be able to determine whether log entries have been deleted or modified in some<br />

way, you can employ a MAC with a sequential nonce. For each log entry that is<br />

made, increment the nonce by one. The log entries can then be checked to ensure<br />

that all nonces are accounted for and that no duplicates have been inserted into the<br />

log file.<br />

See Also<br />

syslog-ng by Balabit IT Security LTD: http://www.balabit.com/products/syslog_ng/<br />

Following Best Practices for Audit Logging | 737<br />

This is the Title of the Book, eMatter Edition<br />

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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