Authentication Protocols in Computer Networks

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Questions and Answers

What is the goal of the authentication protocol in ap3.1?

To authenticate Alice's identity (correct)

To avoid playback attacks

To send encrypted passwords

To share a symmetric key

What is the purpose of the Authentication number in the protocol?

To share a public key

To authenticate Bob's identity

To encrypt the password

To confirm the agency's authority (correct)

What is the requirement for the Authentication number in ap4.0?

It must be used only once in a lifetime (correct)

It must be used multiple times

It must be shared with Bob

It must be encrypted with a public key

How does Alice prove she is 'live' in ap4.0?

By returning R, encrypted with a shared secret key Signup and view all the answers

What is the limitation of ap4.0?

It requires a shared symmetric key Signup and view all the answers

What is the motivation behind ap5.0?

To use public key techniques for authentication Signup and view all the answers

What is the password to enter Moria in the context of J.R.R. Tolkien's story?

Mellon Signup and view all the answers

What is the primary goal of authentication in the context of network communication?

To prove one's identity Signup and view all the answers

What is the flaw in Protocol ap2.0?

Trudy can create a packet spoofing Alice's address Signup and view all the answers

What type of attack can be launched against Protocol ap3.0?

Replay attack Signup and view all the answers

What improvement does Protocol ap3.1 offer over Protocol ap3.0?

Alice's password is encrypted Signup and view all the answers

Why is Protocol ap1.0 not secure?

Trudy can simply declare herself to be Alice Signup and view all the answers

What is the primary purpose of a trusted CA in the SSL protocol?

To enable the browser to extract the server's public key from the certificate Signup and view all the answers

What is the primary weakness in the ap5.0 protocol?

The distribution of public keys Signup and view all the answers

What is the symmetric session key used for in the SSL protocol?

To encrypt all data sent into the TCP socket Signup and view all the answers

What is the purpose of a Key Distribution Center (KDC)?

To act as a trusted intermediary between entities Signup and view all the answers

What is the benefit of using client certificates in SSL?

It enables the server to authenticate the client Signup and view all the answers

What is the problem with public key cryptography?

It is difficult to verify the authenticity of the public key Signup and view all the answers

What is the relationship between SSL and TLS?

SSL is the basis for TLS Signup and view all the answers

What is the role of a Trusted Certification Authority (CA)?

To verify the authenticity of public keys Signup and view all the answers

What is an example of a non-Web application that can use SSL?

IMAP Signup and view all the answers

What is the primary function of a Certificate Authority (CA)?

To bind public keys to particular entities Signup and view all the answers

How does a KDC enable Alice and Bob to communicate with each other?

By establishing a shared symmetric secret key Signup and view all the answers

What is the symmetric key problem?

How to establish a shared secret key over a network Signup and view all the answers

What does Alice use to obtain Bob's public key?

Bob's certificate and CA's public key Signup and view all the answers

What is the purpose of a digital signature in a certificate?

To ensure the integrity of the certificate Signup and view all the answers

What is the primary goal of the Key Distribution Center (KDC) in the KA-KDC protocol?

To distribute session keys for symmetric encryption Signup and view all the answers

What is the primary benefit of using SSL in web browsers?

To provide transport layer security for TCP-based applications Signup and view all the answers

What information does a certificate contain?

All of the above Signup and view all the answers

Study Notes

Authentication

Goal: Bob wants Alice to "prove" her identity to him
Protocol ap1.0: Alice says "I am Alice" (insufficient as Trudy can declare herself to be Alice)
Protocol ap2.0: Alice says "I am Alice" in an IP packet containing her source IP address (Trudy can create a packet "spoofing" Alice's address)
Protocol ap3.0: Alice says "I am Alice" and sends her secret password to "prove" it (vulnerable to playback attack)

Authentication: Another Try

Protocol ap3.1: Alice says "I am Alice" and sends her encrypted secret password to "prove" it (secure against playback attack)
Authentication number: used to confirm the speaker's identity, used only once in a lifetime
Protocol ap4.0: Bob sends Alice an authentication number, R, which Alice must return encrypted with a shared secret key (proves Alice is live and is the only one who knows the key to encrypt R)
Drawback of ap4.0: requires shared symmetric key

Public Key Techniques

Protocol ap5.0: uses authentication number/nonce and public key cryptography (avoids shared symmetric key)
Alice sends "I am Alice" and R, encrypted with her private key, to Bob
Bob computes KA(R) and knows only Alice could have encrypted R such that KA(R) = R

Network Security

Cryptography: symmetric and public, basic techniques and tradeoffs
Authentication: common styles of attack
Key distribution: why it is needed and its uses (secure email, secure transport, IPsec, 802.11 WEP)

Key Distribution

Symmetric key problem: how to establish a shared secret key over a network
Public key problem: how to ensure the public key obtained is genuine and not Trudy's
Solution: trusted intermediaries (Key Distribution Center, KDC, or Trusted Certification Authority, CA)

Key Distribution Center (KDC)

Server shares different secret key with each registered user
Alice and Bob know their own symmetric keys for communicating with KDC
KDC generates R1, which Alice and Bob use as a session key for shared symmetric encryption

Certification Authorities

Certification authority (CA): binds public key to particular entity
Entity registers its public key with CA and provides "proof of identity"
CA creates a certificate binding entity to its public key, digitally signed by CA
Certificate contains entity's public key, identifying information, and digital signature

Secure Sockets Layer (SSL)

Provides transport layer security to any TCP-based application
Security services: server authentication, data encryption, and client authentication (optional)
SSL-enabled browser includes public keys for trusted CAs

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Description

Learn about authentication protocols and goals, including difficulties in verifying identities online. Discover how Alice can prove her identity to Bob in a network.