computer science

Zfone

Zfone is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Zfone rather than just read about it. In short: Zfone is software for secure voice communication over the Internet (VoIP), using the ZRTP protocol. It is created by Phil Zimmermann, the creator of the PGP encryption software.

Key takeaways

Zfone belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Zfone to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Zfone from memory before moving on to harder problems.

Reference excerpt

Zfone is software for secure voice communication over the Internet (VoIP), using the ZRTP protocol. It is created by Phil Zimmermann, the creator of the PGP encryption software. Zfone works on top of existing SIP- and RTP-programs, but should work with any SIP- and RTP-compliant VoIP-program. Zfone turns many existing VoIP clients into secure phones. It runs in the Internet Protocol stack on any Windows XP, Mac OS X, or Linux PC, and intercepts and filters all the VoIP packets as they go in and out of the machine, and secures the call on the fly. A variety of different software VoIP clients can be used to make a VoIP call. The Zfone software detects when the call starts, and initiates a cryptographic key agreement between the two parties, and then proceeds to encrypt and decrypt the voice packets on the fly. It has its own separate GUI, telling the user if the call is secure. Zfone describes itself to end-users as a "bump on the wire" between the VoIP client and the Internet, which acts upon the protocol stack. Zfone's libZRTP SDK libraries are released under either the Affero General Public License (AGPL) or a commercial license. Note that only the libZRTP SDK libraries are provided under the AGPL. The parts of Zfone that are not part of the libZRTP SDK libraries are not licensed under the AGPL or any other open source license. Although the source code of those components is published for peer review, they remain proprietary. The Zfone proprietary license also contains a time bomb provision. It appears that Zfone development has stagnated, however, as the most recent version was released on 22 Mar 2009. In addition, since 29 Jan 2011, it has not been possible to download Zfone from the developer's website since the download server has gone offline.

Platforms and specification Availability – Mac OS X, Linux, and Windows as compiled programs as well as an SDK. Encryption standards – Based on ZRTP, which uses 128- or 256-bit AES together with a 3072-bit key exchange system and voice-based verification to prevent man-in-the-middle attacks. ZRTP protocol – Published as an IETF RFC 6189: "ZRTP: Media Path Key Agreement for Unicast Secure RTP" VoIP clients – Zfone has been tested with the following VoIP clients: X-Lite, Gizmo5, XMeeting, Google Talk VoIP client, and SJphone.

See also Comparison of VoIP software Secure telephone

References

External links Zfone home page Phil Zimmermann official website CNET News: E-mail security hero takes on VoIP 'Wired.com' article April 03 2006

Worked examples

Example 1 — a first encounter with Zfone

Start with the simplest possible case. Write down what Zfone claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Zfone before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Zfone ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Zfone

In research: Zfone appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Zfone in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Zfone is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cryptographic software, Internet privacy software, Software using the GNU Affero General Public License, so understanding it makes those chapters shorter.
In everyday life: Look for Zfone outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Zfone in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Zfone means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Zfone out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Zfone in simple terms?

Zfone is software for secure voice communication over the Internet (VoIP), using the ZRTP protocol. It is created by Phil Zimmermann, the creator of the PGP encryption software.

Why does Zfone matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Zfone?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Zfone.