O

Oakley

The Oakley Session Key Exchange provides a hybrid Diffie-Hellman session key exchange for use within the ISAKMP framework. Oakley provides the important property of Perfect Forward Secrecy (PFS).

octet

A byte. Used instead of "byte" in most IP documents because historically many hosts did not use 8-bit bytes. For a full discussion, read the LiveSecurity article, "Foundations: Understanding IP Addresses and Binary."

one-time pad

A stack of papers bound together, with each paper providing one large, non-repeating set of truly random letters and/or numbers used as an encryption key. Widely used in World War II, the method consisted of using the key on a page exactly once, then tearing off the page and using the key on the next page for the next message. Since the key changes with every message, the enemy does not have a feasible chance to decrypt any given message; thus, one-time pads are considered the only perfect encryption scheme — as long as the bad guys don't intercept a copy of the pad.

one-way hash function

A mathematical process performed on data to produce a numeric result called a message digest, which cannot be reversed to produce the original message.
See hash and message digest.

open source software

A term applied when the source code of a computer program is made available free of charge to the general public. The reason for doing so is that potentially, a larger group of programmers will produce a more useful and bug-free product than a smaller group of programmers, and that more people will use software that is free. The concept relies on peer review to find and eliminate bugs in the program code, which happens at a much quicker rate than with commercial software because the information is shared throughout the open source community instead of through a corporation's smaller, proprietary R & D department. One of the most famous examples of open source software is Linux.

Optional network

A network architecture used by an organization that wants to host its own Internet services without allowing unauthorized access to its private network. Typically, the Optional network contains devices accessible to public Internet traffic, such as Web (HTTP) servers, FTP servers, SMTP (e-mail) servers and DNS servers. Access from the Optional network to the Trusted network can then be appropriately restricted by the firewall. For that reason, some refer to the Optional network as a "semi-public" network.

out-of-band

A management feature that enables the Management Station to communicate with the device via a telephone line and a modem. OOB is very useful for remotely configuring a device when Ethernet access is unavailable.