science

Password Authentication Protocol

Password Authentication Protocol is a 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 Password Authentication Protocol rather than just read about it. In short: Password Authentication Protocol (PAP) is a password-based authentication protocol used by Point-to-Point Protocol (PPP) to validate users. PAP is specified in RFC 1334.

Key takeaways

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

Reference excerpt

Password Authentication Protocol (PAP) is a password-based authentication protocol used by Point-to-Point Protocol (PPP) to validate users. PAP is specified in RFC 1334. Almost all network operating systems support PPP with PAP, as do most network access servers. PAP is also used in PPPoE, for authenticating DSL users. As the Point-to-Point Protocol (PPP) sends data unencrypted and "in the clear", PAP is vulnerable to any attacker who can observe the PPP session. An attacker can see the users name, password, and any other information associated with the PPP session. Some additional security can be gained on the PPP link by using CHAP or EAP. However, there are always tradeoffs when choosing an authentication method, and there is no single answer for which is more secure. When PAP is used in PPP, it is considered a weak authentication scheme. Weak schemes are simpler and have lighter computational overhead than more complex schemes, such as Transport Layer Security (TLS), but they are much more vulnerable to attack. Weak schemes are used where the transport layer is expected to be physically secure, such as a home DSL link. Where the transport layer is not physically secure a system such as TLS or Internet Protocol Security (IPsec) is used instead.

Other uses of PAP PAP is also used to describe password authentication in other protocols such as RADIUS and Diameter. However, those protocols provide for transport or network layer security, and therefore that usage of PAP does not have the security issues seen when PAP is used with PPP.

Benefits of PAP When the client sends a clear-text password, the authentication server will receive it, and compare it to a "known good" password. Since the authentication server has received the password in clear-text, the format of the stored password can be chosen to be secure "at rest". If an attacker were to steal the entire database of passwords, it is computationally infeasible to reverse the function to recover a plaintext password. As a result, while PAP passwords are less secure when sent over a PPP link, they allow for more secure storage "at rest" than with other methods such as CHAP.

Working cycle PAP authentication is only done at the time of the initial link establishment, and verifies the identity of the client using a two-way handshake.

Client sends username and password. This is sent repeatedly until a response is received from the server. Server sends authentication-ack (if credentials are OK) or authentication-nak (otherwise)

PAP packets

PAP packet embedded in a PPP frame. The protocol field has a value of C023 (hex).

Worked examples

Example 1 — a first encounter with Password Authentication Protocol

Start with the simplest possible case. Write down what Password Authentication Protocol claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In 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 Password Authentication Protocol 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 Password Authentication Protocol 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 Password Authentication Protocol

In research: Password Authentication Protocol appears in 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 Password Authentication Protocol 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: Password Authentication Protocol is common in secondary-school and first-year university syllabi. It links to neighbouring topics Authentication protocols, Internet protocols, Password authentication, so understanding it makes those chapters shorter.
In everyday life: Look for Password Authentication Protocol 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 Password Authentication Protocol in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Password Authentication Protocol 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 Password Authentication Protocol out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Password Authentication Protocol in simple terms?

Password Authentication Protocol (PAP) is a password-based authentication protocol used by Point-to-Point Protocol (PPP) to validate users. PAP is specified in RFC 1334.

Why does Password Authentication Protocol matter?

Because it connects several 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 Password Authentication Protocol?

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 Password Authentication Protocol.