Asymmetric encryption, also known as public key cryptography, uses two different keys for

encryption and decryption: a public key and a private key. The public key can be shared with anyone,

while the private key must be kept secret. Data encrypted with the public key can only be decrypted

with the private key, and vice versa. This ensures that only the intended recipient can access the

encrypted data, and that the sender can prove their identity with a digital signature. Asymmetric

encryption is widely used for securing Internet communications, such as TLS/SSL, which enables

HTTPS. Some examples of asymmetric encryption algorithms are RSA, Diffie-Hellman, and Elliptic

Curve Cryptography. The other options are not correct because they do not use a public key and

private key. Symmetric encryption uses the same key for encryption and decryption, and is faster and

more efficient than asymmetric encryption. However, symmetric encryption requires a secure way to

exchange the key between the sender and the receiver, which can be facilitated by asymmetric

encryption. Linear and nonlinear encryption are not types of encryption, but rather properties of

encryption algorithms. A linear encryption algorithm is one that can be expressed as a linear

function, such as XOR. A nonlinear encryption algorithm is one that involves more complex

mathematical operations, such as modular arithmetic or S-boxes. Nonlinear encryption algorithms

are generally more secure and resistant to cryptanalysis than linear encryption

algorithms. Reference :=

Public-key cryptography - Wikipedia

How does public key cryptography work? - Cloudflare

Public and private encryption keys | PreVeil

AES encryption, what are public and private keys?

IKEv1 has two modes of operation: main mode and aggressive mode. Main mode uses six messages

to establish the IKE SA, while aggressive mode uses only three messages. Therefore, aggressive

mode is faster than main mode, but less secure, as it exposes the identities of the peers in cleartext.

This makes it vulnerable to man-in-the-middle attacks. IKEv2 does not have these modes, but uses a

single four-message exchange to establish the IKE SA. IKEv2 also encrypts the identities of the peers,

making it more secure than IKEv1 aggressive mode.

IKEv1 uses EAP authentication only for remote access VPNs, not for site-to-site VPNs. IKEv2 supports

EAP authentication for both types of VPNs. EAP authentication allows the use of various

authentication methods, such as certificates, tokens, or passwords.

IKEv1 conversations are initiated by the ISAKMP header, which contains the security parameters and

the message type. IKEv2 conversations are initiated by the IKE_SA_INIT message, which contains the

security parameters, the message type, and the message ID. The message ID is used to identify and

order the messages in the IKEv2 exchange.

NAT-T is supported by both IKEv1 and IKEv2. NAT-T stands for Network Address Translation-Traversal,

and it is a mechanism that allows IKE and IPsec traffic to pass through a NAT device. NAT-T detects

the presence of NAT and encapsulates the IKE and IPsec packets in UDP headers, so that they can be

translated by the NAT device. Reference:

IKEv1 vs IKEv2 – What is the Difference?

Comparison between IKEv1 and IKEv2

IKEv2 vs IKEv1: What are the differences?

IOS zone-based firewalls (ZBFW) are a feature that provides stateful firewall policies between groups

of interfaces known as zones. A zone is a logical grouping of one or more interfaces that have similar

security requirements. A zone can be applied to physical interfaces, subinterfaces, port channels,

VLAN interfaces, or tunnel interfaces. However, an interface can be assigned only to one zone, and it

cannot be shared between zones. This is because the ZBFW policy is applied between zones, not

interfaces, and it controls the bidirectional traffic flow between them. Therefore, an interface can

belong to only one zone at a time, and it must be removed from one zone before it can be added to

another zone. This ensures that the firewall policy is consistent and unambiguous for each interface.

Reference :=

Security Configuration Guide: Zone-Based Policy Firewall, Cisco IOS XE Gibraltar 16.12.x, Configuring

Zones

Understand the Zone-Based Policy Firewall Design, Zone-Based Policy Overview

IOS Zone Based Firewall Step-by-Step Basic Configuration, Zone Based Firewall Vs CBAC

An active/active FlexVPN configuration allows for multiple routers or VRFs to act as hubs for different

VPN groups, providing load balancing and redundancy1. This is useful when the VPN deployment has

a large number of spokes or different security policies for different groups of spokes. DMVPN, on the

other hand, only supports a single hub or a pair of hubs in active/standby mode for each VPN group2.

This limits the scalability and flexibility of DMVPN deployments. Therefore, an engineer would opt

for an active/active FlexVPN configuration as opposed to DMVPN when multiple routers or VRFs are

required. Reference :=

Cisco FlexVPN: Benefits and Best Practices

Cisco DMVPN Design Guide

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The debug crypto isakmp sa command shows the status of the Internet Security Association and Key

Management Protocol (ISAKMP) security associations (SAs). The output of this command indicates

that the ISAKMP negotiation failed after several retransmissions. The most likely cause of this failure

is a mismatch in the authentication key between the two peers. The authentication key is specified

by the crypto isakmp key command and must be the same on both routers. If the authentication key

is different, the ISAKMP messages cannot be decrypted and verified by the peers, resulting in an

error. To fix this problem, the network administrator should verify and correct the authentication key

on both routers and clear the existing ISAKMP SAs with the clear crypto isakmp sa

command. Reference: 1, 2, 3, 4

Time synchronization is one of the features that can be configured for managed devices in the device

platform settings of the Firepower Management Center (FMC). Time synchronization ensures that

the FMC and its managed devices have the same date and time settings, which is important for

accurate event logging and reporting. The FMC can act as a Network Time Protocol (NTP) server for

its managed devices, or it can use an external NTP server as a time source1. The FMC can also

synchronize its time with the system clock of the device where it is

installed2. Reference := 1: Firepower Management Center Device Configuration Guide, 7.1 - Platform

Settings 2: Firepower Management Center Configuration Guide, Version 6.6 - Device Management

Basics

Secret key cryptography, also known as symmetric key cryptography, is a type of encryption where a

single secret key is used for both encryption and decryption of a message. The cryptographic key is

kept secret between the sender and receiver, making it difficult for anyone else to decipher the

message. Some of the functions of secret key cryptography are:

Key selection without integer factorization: Secret key cryptography does not rely on complex

mathematical problems such as integer factorization or discrete logarithms to generate keys.

Instead, the keys are chosen randomly or derived from a passphrase or a shared secret. This makes

the key generation process faster and simpler than in public key cryptography.

Utilization of less memory: Secret key cryptography uses less memory than public key cryptography,

as it only requires one key to be stored and managed. Public key cryptography, on the other hand,

requires two keys (public and private) for each user, which increases the memory overhead and

complexity of key management.

The other options are not functions of secret key cryptography, but rather characteristics of public

key cryptography or asymmetric cryptography, which is a different type of encryption where different

keys are used for encryption and decryption. Public key cryptography has the following features:

Utilization of different keys for encryption and decryption: Public key cryptography uses a pair of

keys, one public and one private, for each user. The public key can be shared with anyone, while the

private key must be kept secret. The public key is used to encrypt messages, while the private key is

used to decrypt them. This allows users to communicate securely without having to exchange a

secret key beforehand.

Utilization of large prime number iterations: Public key cryptography relies on hard mathematical

problems such as integer factorization or discrete logarithms to generate keys. These problems

involve finding the prime factors of large numbers or finding the discrete logarithms of numbers in a

finite field. These problems are easy to solve in one direction, but hard to solve in the reverse

direction. For example, it is easy to multiply two large prime numbers, but hard to find the prime

factors of the product. This makes the keys hard to break by brute force or other methods.

Provides the capability to only know the key on one side: Public key cryptography enables users to

encrypt messages without knowing the recipient’s key, and vice versa. This is possible because the

encryption and decryption keys are different and mathematically related. For example, Alice can

encrypt a message with Bob’s public key, and only Bob can decrypt it with his private key. Alice does

not need to know Bob’s private key, and Bob does not need to know Alice’s key. This also enables

public key cryptography to support digital signatures, which are a way of verifying the identity and

integrity of a message.

Reference :=

What Is Secret Key Cryptography? A Complete Guide - Helenix

Definition of Secret-key Cryptography - Gartner

Patching is important for security, compliance, stability, and reputation reasons. Patches are released

to fix security vulnerabilities in software and systems, which can be exploited by cybercriminals to

cause data breaches, data loss, or other damage. Failure to patch these vulnerabilities leaves the

company’s systems exposed to potential security risks. Patch management helps to minimize these

risks by ensuring that all software and systems are up-to-date with the latest security patches. Patch

management also helps to comply with regulatory and industry standards that require a certain level

of security, and to avoid legal consequences for non-compliance. Additionally, patches provide bug

fixes and other updates that improve the stability and performance of software and systems, and

prevent system crashes, downtime, and other issues that can negatively impact the business

operations. Finally, patch management helps to maintain a positive reputation for the company, as a

security breach or downtime caused by unpatched vulnerabilities can damage the customer trust

and loyalty, and result in revenue loss. Reference:

5 Patch Management Best Practices for Success in 2023 - TechRepublic

Six Patch Management Best Practices

[Updated 2024] - Heimdal Security

REST stands for Representational State Transfer, which is an architectural style for designing web

services. RESTful web services use HTTP as the application protocol and support the standard HTTP

methods, such as GET, PUT, POST, and DELETE, to perform CRUD (Create, Read, Update, Delete)

operations on resources. Cisco DNA Center exposes its functionality through a set of RESTful APIs

that allow external applications to interact with the network controller and automate various

tasks. The RESTful architecture used within Cisco DNA Center has the following characteristics12:

It is simple, extensible, and secure to use. The APIs are based on open standards and use JSON as the

data format. The APIs also support HTTPS for secure communication and authentication.

It is stateless, meaning that each request contains all the information necessary to process it, and the

server does not store any session or client state. This improves scalability and performance of the

web services.

It is resource-oriented, meaning that each API endpoint represents a logical entity or a resource that

can be manipulated by the HTTP methods. For example, the /dna/intent/api/v1/network-

device endpoint represents the network devices resource, and the GET method can be used to

retrieve the list of network devices from Cisco DNA Center.

It is uniform, meaning that the same interface and conventions are used across all the APIs. For

example, the APIs use the same authentication mechanism, error handling, pagination, filtering, and

sorting parameters. Reference:

1: Introduction to Cisco DNA Center REST APIs - Cisco DevNet Learning Labs

2: Cisco DNA Center Platform User Guide, Release 2.2.3