Key Management and Symmetric Key Distribution

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Questions and Answers

What is the primary purpose of cryptographic key management?

To create public keys for encryption

To administer cryptographic keys for a system (correct)

To replace outdated cryptographic algorithms

To monitor data traffic in a network

Which of the following is NOT a key distribution alternative for symmetric key sharing?

Third party delivery of the key

Use of public key infrastructure (correct)

Physical delivery of a key by one party

Using previous keys to encrypt new keys

In a distributed system with n hosts, how many keys are required for complete pairwise communication?

$n(n - 1)/2$ (correct)

$2n - 1$

$n^2 - 1$

$n(n + 1)/2$

What can lead to a security failure in a symmetric key distribution system?

Break in the key distribution scheme Signup and view all the answers

Which aspect does key management NOT typically include?

Replacement of cryptographic algorithms Signup and view all the answers

What is a major weakness of PGP keys when appended to email messages?

Forgery by anyone claiming to be someone else Signup and view all the answers

Which property is NOT a requirement for a trusted public directory?

Requires real-time access to the directory Signup and view all the answers

What role do public-key certificates play in key exchange?

They allow key exchange without real-time access to public-key authority Signup and view all the answers

What is a key characteristic of a public-key authority compared to a public directory?

Users must know the public key for the directory Signup and view all the answers

What additional information is typically included in a public-key certificate?

Period of validity and rights of use Signup and view all the answers

What is the role of a session key in key hierarchy?

It is a temporary key used for encrypting data between users. Signup and view all the answers

Why are public key cryptosystems generally not used for direct data encryption?

They are inefficient for direct data encryption. Signup and view all the answers

What limitation should be placed on session key lifetimes?

They should be limited for greater security. Signup and view all the answers

What is the primary purpose of using asymmetric encryption in symmetric key distribution?

To encrypt secret keys for distribution. Signup and view all the answers

In hybrid key distribution, what is shared with each user?

A secret master key. Signup and view all the answers

What is a potential issue when using hierarchies of Key Distribution Centers (KDCs)?

Each KDC must trust other KDCs. Signup and view all the answers

What is a public-key certificate used for?

To verify the ownership of a public key. Signup and view all the answers

Which of the following describes a Man-in-the-Middle-Attack?

An attack where the interceptor reads, alters or injects data. Signup and view all the answers

Study Notes

Key Management

Key Management is a process that handles all aspects of cryptographic keys, including generation, creation, protection, storage, exchange, replacement, and usage.
Key management also controls access and records every key access, use, and context.
Key management is essential for the security of any cryptosystem.

Symmetric Key Distribution Using Symmetric Encryption

Symmetric schemes require both parties to share a common secret key.
The problem is how to distribute this key securely while protecting it from unauthorized access.
Frequent key changes are desirable for enhanced security.
Often, system failures occur due to breaches in the key distribution scheme.
If there are n hosts, the number of required keys for a distributed system is n(n-1)/2.
A network with 1000 nodes could require half a million keys for node-level encryption and 50 million keys for application-level encryption.

Key Hierarchy

A hierarchy of keys is often used to manage key distribution.
Session Key: Temporary key used for data encryption between users during a specific session. Discarded after the session.
Master Key: Used to encrypt session keys and shared between the user and the key distribution center.

Key Distribution Issues

Key Distribution Centers (KDCs) are required for large networks, and they must trust each other.
Session key lifetimes should be limited for enhanced security.
Automatic key distribution can be used on behalf of users, but trust in the system is essential.
Decentralized key distribution is suitable for smaller networks.

Symmetric Key Distribution Using Asymmetric Encryption

Public-key cryptosystems are generally less efficient for direct data encryption.
Instead, they are used to encrypt secret keys for distribution purposes.

Simple Secret Key Distribution

Proposed by Merkle, this simple scheme enables secure communication without needing pre-existing keys.

Man-in-the-Middle Attack

This attack exploits the lack of authentication and confidentiality in basic key distribution systems.

Secret Key Distribution with Confidentiality and Authentication

This approach ensures both confidentiality and authentication during key distribution.

Hybrid Key Distribution

Incorporates both private-key and public-key cryptography.
A KDC shares a secret master key with each user.
Session keys are distributed using the master key.
Public keys are used to distribute master keys, particularly useful for widely distributed users.

Distribution of Public Keys

Public keys can be distributed through:
Public Announcement
Publicly Available Directory
Public-Key Authority
Public-Key Certificates

Public Announcement

Users can distribute their public keys directly to recipients or broadcast them to the community.
A major weakness is forgery, as anyone can create a bogus key and claim it as belonging to another user.

Publicly Available Directory

Keys can be registered securely with a trusted directory containing entries for {name, public-key}.
Users can replace their keys at any time, and the directory is periodically published for access.
While more secure than public announcement, it remains vulnerable to tampering or forgery

Public-Key Authority

Tightens control over key distribution from the directory.
Users must know the public key of the public-key authority.
Securely obtains public keys from the directory, requiring real-time access.
Still potentially vulnerable to tampering.

Public-Key Certificate

Enables key exchange without real-time access to the public-key authority.
A certificate securely binds an identity to a public key, including additional information such as validity period, rights of use, etc.
The contents are signed by a trusted public key or certificate authority (CA).
Can be verified by anyone who knows the public-key authority's public key.

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Description

This quiz explores the essential concepts of key management and symmetric key distribution. It covers the processes involved in cryptographic key handling and the security implications of distributing symmetric keys in a network. Test your understanding of key hierarchies and distribution challenges.