ECCouncil 312-50v12 Practice Test - Questions Answers, Page 51

Censys scans help the scientific community accurately study the Internet. The data is sometimes used to detect security problems and to inform operators of vulnerable systems so that they can fixed

-A: Perform an aggressive scan which select most of the commonly used options within nmap

-Pn: Means Don't ping -p:scan specific ports -sT: TCP Connect scan -O: Operating system detection -T0: timing template (extremely slow- evade FW)

A SYN flood attack is a type of denial-of-service (DoS) attack that exploits the TCP handshake process by sending a large number of SYN requests to the target server, without completing the connection. This consumes the connection state tables on the server, preventing it from accepting new connections. The attacker has crafted an automated botnet to simultaneously send 's' SYN packets per second to the server. The server can handle 'f' SYN packets per second without any performance issues. If 's' exceeds 'f', the network infrastructure begins to show signs of overload. The system's response time increases exponentially (24k), where 'k' represents each additional SYN packet above the 'f' limit.

Considering 's=500' and different 'f' values, the scenario that is most likely to cause the server to experience overload and significantly increased response times is the one where 'f=420'. This is because 's' is greater than 'f' by 80 packets per second, which means the server cannot handle the incoming traffic and will eventually run out of resources. The response time shoots up (2480 = 281,474,976,710,656 times the normal response time), indicating a system overload.

The other scenarios are less likely or less severe than the one where 'f=420'. Option A has 'f=510', which is greater than 's', so the system stays stable and the response time remains unaffected. Option B has 'f=495', which is less than 's' by 5 packets per second, so the response time drastically rises (245 = 32 times the normal response time), indicating a probable system overload, but not as extreme as option D. Option C has 'f=505', which is less than 's' by 5 packets per second, so the response time increases but not as drastically (245 = 32 times the normal response time), and the system might still function, albeit slowly.Reference:

SYN flood DDoS attack | Cloudflare

SYN flood - Wikipedia

What Is a SYN Flood Attack? | F5

What is a SYN flood attack and how to prevent it? | NETSCOUT

A thin Whois model is a type of data model that is used by some domain registrars for storing and looking up Whois information. In a thin Whois model, the registrar only stores the basic information about the domain, such as the domain name, the registrar name, the name servers, and the registration and expiration dates. The rest of the information, such as the contact details of the domain owner, the administrative contact, and the technical contact, is stored by the registry that manages the top-level domain (TLD) of the domain. For example, the registry for .com and .net domains is Verisign, and the registry for .org domains is Public Interest Registry.When a Whois lookup is performed on a domain that uses a thin Whois model, the registrar's Whois server only returns the basic information and refers the query to the registry's Whois server for the complete information1.

As a hacker, if you are unable to gather complete Whois information from the registrar for a particular set of data, it might be because the domain's registrar is using a thin Whois model and the registry's Whois server is not responding or providing the information. This could be due to various reasons, such as network issues, server errors, rate limits, privacy policies, or legal restrictions. Therefore, the probable data model being utilized by the domain's registrar for storing and looking up Whois information is a thin Whois model working correctly.

Differences Between Thin WHOIS vs Thick WHOIS -- OpenSRS Help & Support

A Denial of Service (DoS) attack is a type of cyberattack that aims to make a machine or network resource unavailable to its intended users by flooding it with traffic or requests that consume its resources. A TCP SYN flood attack is a type of DoS attack that exploits the TCP handshake process by sending a large number of SYN requests to the target server, without completing the connection. A UDP flood attack is a type of DoS attack that sends a large number of UDP packets to random ports on the target server, forcing it to check for the application listening at that port and reply with an ICMP packet. An ICMP flood attack is a type of DoS attack that sends a large number of ICMP packets, such as ping requests, to the target server, overwhelming its ICMP processing capacity.

The attacker's strategy involves a unique mixture of TCP SYN, UDP, and ICMP floods, using 'r' packets per second. The server can handle 'h' packets per second before it starts showing signs of strain. If 'r' surpasses 'h', it overwhelms the server, causing it to become unresponsive. The attacker selects 'r' as a composite number and 'h' as a prime number, making the attack detection more challenging. This is because prime numbers are less predictable and more difficult to factorize than composite numbers, which may hinder the analysis of the attack pattern.

Considering 'r=2010' and different values for 'h', the scenario that would potentially cause the server to falter is the one where 'h=1987' (prime). This is because 'r' is greater than 'h' by 23 packets per second, which means the server cannot handle the incoming traffic and will eventually run out of resources. The other scenarios would not cause the server to falter, as 'h' is either greater than or very close to 'r', which means the server can either manage or barely cope with the incoming traffic.Reference:

What is a denial-of-service (DoS) attack? | Cloudflare

Denial-of-Service (DoS) Attack: Examples and Common Targets - Investopedia

DDoS Attack Types: Glossary of Terms

What is a Denial of Service (DoS) Attack? | Webopedia

One of the most important actions to secure a web server from common threats is to regularly update and patch the server software. This includes the operating system, the web server software, the database software, and any other applications or frameworks that run on the server. Updating and patching the server software can fix known vulnerabilities, bugs, or errors that could be exploited by attackers to compromise the server or the website. Failing to update and patch the server software can expose the server to common attacks, such as SQL injection, cross-site scripting, remote code execution, denial-of-service, etc.

Installing a web application firewall, limiting the number of concurrent connections to the server, and encrypting the company's website with SSL/TLS are also good practices to secure a web server, but they are not as critical as updating and patching the server software. A web application firewall can filter and block malicious requests, but it cannot prevent attacks that exploit unpatched vulnerabilities in the server software. Limiting the number of concurrent connections to the server can prevent overload and improve performance, but it cannot stop attackers from sending malicious requests or payloads. Encrypting the company's website with SSL/TLS can protect the data in transit between the server and the client, but it cannot protect the data at rest on the server or prevent attacks that target the server itself.

Therefore, the priority action to secure a web server from common threats is to regularly update and patch the server software.

Web Server Security- Beginner's Guide - Astra Security Blog

Top 10 Web Server Security Best Practices | Liquid Web

21 Server Security Tips & Best Practices To Secure Your Server - phoenixNAP

snmp-check (snmp_enum Module) is the best tool to help the ethical hacker to get the information without directly modifying any parameters within the SNMP agent's MIB. snmp-check is a tool that allows the user to enumerate SNMP devices and extract information from them. It can gather a wide array of information about the target, such as system information, network interfaces, routing tables, ARP cache, installed software, running processes, TCP and UDP services, user accounts, and more. snmp-check can also perform brute force attacks to discover the SNMP community strings, which are the passwords used to access the SNMP agent. snmp-check is available as a standalone tool or as a module (snmp_enum) within the Metasploit framework.

The other options are not as effective or suitable as snmp-check for the ethical hacker's task. Nmap is a network scanning and enumeration tool that can perform various types of scans and probes on the target. It can also run scripts to perform specific tasks, such as retrieving SNMP information. However, Nmap may not be able to gather as much information as snmp-check, and it may also trigger alerts or blocks from firewalls or intrusion detection systems. Oputils is a network monitoring and management toolset that can perform various functions, such as device discovery, configuration backup, bandwidth monitoring, IP address management, and more. However, Oputils is mainly designed for device management and not SNMP enumeration, and it may not be able to extract valuable network information from the SNMP agent. SnmpWalk is a tool that allows the user to retrieve the entire MIB tree of an SNMP agent by using SNMP GETNEXT requests. However, SnmpWalk is not suitable for the ethical hacker's task, because it requires the user to change an OID (object identifier) to a different value, which may modify the parameters within the SNMP agent's MIB and affect its functionality or security.Reference:

snmp-check - The SNMP enumerator

SNMP Enumeration | Ethical Hacking - GreyCampus

SNMP Enumeration - GeeksforGeeks

Nmap - the Network Mapper - Free Security Scanner

OpUtils - Network Monitoring & Management Toolset

SnmpWalk - SNMP MIB Browser

A hybrid encryption system is a system that combines the advantages of both asymmetric and symmetric encryption algorithms. Asymmetric encryption, such as RSA, uses a pair of keys: a public key and a private key, which are mathematically related but not identical. Asymmetric encryption can provide key exchange, authentication, and non-repudiation, but it is slower and less efficient than symmetric encryption. Symmetric encryption, such as AES, uses a single key to encrypt and decrypt data. Symmetric encryption is faster and more efficient than asymmetric encryption, but it requires a secure way to share the key.

In a hybrid encryption system, RSA encryption is used for key exchange, and AES encryption is used for data encryption. This way, the system can benefit from the security of RSA and the speed of AES. However, the system also depends on the key sizes of both algorithms, which affect the security and performance of the system.

The key size of RSA encryption determines the number of bits in the public and private keys. The larger the key size, the more secure the encryption, but also the slower the key generation and encryption/decryption processes. The time complexity of generating an RSA key pair is O(n*2), where n is the key size in bits. This means that the time required to generate an RSA key pair increases quadratically with the key size. For example, if it takes 1 second to generate a 1024-bit RSA key pair, it will take 4 seconds to generate a 2048-bit RSA key pair, and 16 seconds to generate a 4096-bit RSA key pair.

The key size of AES encryption determines the number of bits in the symmetric key. The larger the key size, the more secure the encryption, but also the more rounds of encryption/decryption are needed. The time complexity of AES encryption is O(n), where n is the key size in bits. This means that the time required to encrypt/decrypt data increases linearly with the key size. For example, if it takes 1 second to encrypt/decrypt data with a 128-bit AES key, it will take 2 seconds to encrypt/decrypt data with a 256-bit AES key, and 4 seconds to encrypt/decrypt data with a 512-bit AES key.

An attacker has developed a quantum algorithm with time complexity O((log n)*2) to crack RSA encryption. This means that the time required to break RSA encryption decreases exponentially with the key size. For example, if it takes 1 second to break a 1024-bit RSA encryption, it will take 0.25 seconds to break a 2048-bit RSA encryption, and 0.0625 seconds to break a 4096-bit RSA encryption. This makes RSA encryption vulnerable to quantum attacks, unless the key size is very large.

Given n=4000 and variable AES key size, the scenario that is likely to provide the best balance of security and performance is C. AES key size=192 bits. This configuration is a compromise between options A and B, providing moderate security and performance. Option A, AES key size=128 bits, provides less security than option C, but RSA key generation and AES encryption will be faster. Option B, AES key size=256 bits, provides more security than option C, but RSA key generation may be slow. Option D, AES key size=512 bits, provides the highest level of security, but at a significant performance cost due to the large AES key size.

Hybrid cryptosystem - Wikipedia

RSA (cryptosystem) - Wikipedia

Advanced Encryption Standard - Wikipedia

Quantum computing and cryptography - Wikipedia