Beihang University Network Security Final Test Center Reference

written in front

A brief summary of the 2022 Beihang Network Security Final Exam test points (up to Chapter 11), you can use as a reference when reviewing, please refer to the teacher's courseware and textbook (Network Security - Technology and Practice, edited by Liu Jianwei) for details. Due to the average level of the author, it is inevitable to make mistakes when summarizing, please make more comments and corrections.

Chapter 1 Introduction

1. Master the four goals of information security

Confidentiality, Integrity, Availability, Lawful Use

2. What are the common threats in information systems?

Authorization Violations, Impersonation Attacks, Bypass Control, Trojan Horses or Trapdoors, Media Waste

3. What is a security policy? How many levels are security policies divided into?

A security policy is a set of rules imposed on all security-related activities within a certain security domain.

Divided into three levels (1) security policy objectives (2) institutional security policies (3) system security policies

4. What is an access control policy? Which two categories does it fall into? What is the difference?

Access control policies are part of system-level security policies that force computer systems and networks to automatically enforce authorization.

Divided into mandatory access control policies and autonomous access control policies.

Mandatory access control policies are enforced by authorities in the security domain and cannot be avoided by anyone.

The autonomous access control policy provides specific users with the right to access resources, which can be used to control further access to resources by these users.

5. How many types of security attacks are there? What's the difference?

Divided into passive attack and active attack

Passive attack is to eavesdrop and monitor the transmitted information. Active attack refers to attacks such as maliciously tampering with data or forging data streams. Active attack not only eavesdrops on information, but also tampers with it.

6. Memorize the 5 types of security services and 8 specific security mechanisms in the X.800 standard, and briefly describe the relationship between security services and security mechanisms

5 types of security services

Authentication, access control, data confidentiality, data integrity, non-repudiation

8 specific security mechanisms

Encryption, digital signatures, access control, data integrity, authentication exchange, traffic padding, routing control, notarization

Relationship: Security services implement security policies through security mechanisms.

7. Able to draw network security reference model and network access reference model

Cyber ​​Security Reference Model

Network Access Reference Model

Chapter 2 Basics of Computer Networks

1. Familiarize yourself with the seven-layer reference model of OSI and the four-layer model of TCP/IP

OSI seven-layer reference model

Physical layer, data link layer, network layer, transport layer, session layer, presentation layer, application layer

TCP/IP four-layer reference model

network interface layer, internet layer, transport layer, application layer

2. What is a link-oriented service? What is an unlinked service?

Link-oriented services require both communicating parties to first establish a connection before transmitting data. The data transmission process includes three stages: connection establishment, data transmission and connection release.

The connectionless service does not require the communication parties to establish a connection before transmitting data, and is a "best effort delivery" service.

3. You must know the format and length of IPv4 and IPv6 addresses

IPv4: 32 bits

IPv6: 128 bits

4. You must know the length of the MAC address

48 bits

5. Which network protocol does IP address and MAC address conversion rely on?

ARP protocol

6. What are the classifications of IPv4 addresses? Given an IP address, it is necessary to be able to analyze and determine which type of address the address belongs to.

five kinds.

A: 1.0.0.0 – 127.255.255.255

B: 128.0.0.0-191.255.255.255

C: 192.0.0.0-223.255.255.255

D: 224.0.0.0- 239.255.255.255

E: 240.0.0.0-247.255.255.255

7. Given an IPv4 address and subnet mask, it is required to be able to calculate the network address.

8. Familiar with the expression method of CIDR, such as: what is the address block range and subnet mask represented by 128.14.32.0/20?

Subnet address range 128.14.32.1 - 128.14.47.254

Subnet mask 255.255.240.0

9. What is "port number"? What role does "port number" play in network communication?

The port number is used to identify the application process according to the function of the application process. The port number and IP address together form a socket socket, which is used to uniquely identify a certain process on a certain host.

Chapter 3 Security of Internet Protocols

1. Memorize the functions of communication protocols such as http/ftp/telnet/pop3/smtp/imap/ssh/dns.

See table below.

2. Memorize the port numbers of some commonly used network protocols.

protocol	The port number	Function
http	80	Used to transmit web data
ftp	20、21	Provide file upload and download services
telnet	23	Telnet service
pop3	110	receive e-mail
smtp	25	send email
imap	143	receive e-mail
ssh	22	Implement secure remote login
dns	53	Realize conversion of domain name and IP address
snmp	UDP 161	Realize network element management
ntp	UDP 123	Make the clocks of all devices in the network consistent

3. What are the Internet layer protocols? What are the transport layer protocols? What are the application layer protocols?

Internet layer: IP, ARP, ICMP, IGMP, OSPF, BGP protocols

Transport layer: TCP, UDP protocol

Application layer: RIP, HTTP, TELNET, SSH, DNS, SMTP, MIME, POP3, IMAP, PGP, FTP, TFTP, NFS, SNMP, DHCP, H.323, SIP, NTP, FINGER, Whois, LDAP, NNTP protocol

4. Why is Network Address Translation (NAT) necessary?

Solve the problem of IP address shortage

5. What is the function of the ARP protocol?

Responsible for converting the 32b IP address in the LAN to the corresponding 48b physical address, that is, the MAC address of the network card

6. Why is UDP more vulnerable to attacks than TCP?

Because UDP does not have the process of exchanging handshake information and sequence numbers

7. Compared with the POP3 protocol, what are the security improvements of the IMAP protocol?

IMAP is distributed, with digest reading, optional download of attachments, server caching.

8. Compared with the Telnet protocol, what are the security improvements of the SSH protocol?

Telnet is plaintext transmission; ssh is encrypted transmission and supports compression.

ssh uses the public key to authenticate the user of the accessed server, further improving security; telnet does not use the public key.

9. What is ICMP redirection attack? How to prevent such attacks?

Attackers can use ICMP to redirect messages, making the target machine suffer from connection hijacking and denial of service attacks.

Disable the ICMP function in the firewall; the firewall should have state detection, detailed data packet integrity inspection and good filtering rule control functions.

10. In the network, why can't a data packet come from the host with that IP address just by identifying the IP address of the data packet?

The IP layer cannot guarantee that the IP datagram must be sent from the source address. An attacker can masquerade as another network host and send data packets containing a forged source address to deceive the recipient. (IP spoofing attack)

Chapter 4 Single Key Cryptosystem

1. According to the different processing methods for plaintext messages, what two types of single-key systems can be divided into?

Stream Ciphers and Block Ciphers

2. What are the two commonly used transformations in classical ciphers?

Replacement and Substitution

3. What is theoretical security? What is Computationally Secure? How many theoretically secure cryptographic algorithms are there? What is a theoretically secure password?

Theoretical security: the attacker has unlimited time and resources and remains safe, also known as unconditional security

Computational Security: Cannot be breached within a given time and resources, related to the attacker's ability and target conditions

one time pad

4. What are synchronous stream ciphers and self-synchronizing stream ciphers? What does the security of a stream cipher depend on?

In synchronous stream ciphers, the internal state in the key stream generator has nothing to do with the plaintext message, that is, the key stream is independent of the plaintext

In self-synchronizing stream ciphers, the key stream is related to the plaintext.

Security depends on the strength of pseudo-random numbers

5. What are the DES packet length, key length, and number of rounds? What transformations are included in 1 round of encryption? What is the nonlinear transformation in DES? (this is not sure)

Packet length: 64

Key length: 56

Number of rounds: 16

Eight "substitution boxes" (S boxes) permutation, that is, compression transformation.

6. What are the AES packet length, key length, and number of rounds? What transformations are included in 1 round of encryption? What is the non-linear transform included in AES?

Packet length: 128

Key length: 128/192/256, corresponding to encryption rounds 10/12/14

7. Is the more encryption rounds the better? Are longer keys better? Is it necessarily more secure to encrypt data by connecting two algorithms in series?

No, no, no.

8. What are the 5 working modes of the block cipher? Can draw the functional block diagram of 5 working modes.

(1) Codebook Mode ECB

(2) Cipher block chaining mode CBC

(3) Output feedback mode OFB

(4) Cipher Feedback Mode CFB

(5) Counter mode CTR

9. Analyze the 5 encryption modes, which encryption modes have no error extension? Which have error extension? If there is error propagation, how many packets are affected?

OFB and CTR without error extension

ECB only current group

CBC only has the current packet and the next packet

CFB current and subsequent groups, a total of $\lceil \frac{n}{s}\rceil +1$ group

10. Understand the Chinese commercial block cipher algorithm SM4, know its block length, key length and number of encryption rounds.

Packet length 128

key length 128

Number of encryption rounds 32

Chapter 5 Dual-Key Cryptography

1. The dual-key encryption system is constructed based on mathematical problems. Please list the existing mathematical problems. Whose public key is used when encrypting with a dual-key system? Whose private key is used for decryption?

Large integer factorization, discrete logarithm, knapsack problem, quadratic remainder problem, polynomial root finding, etc.

receiver public key, receiver private key

2. What kind of mathematical puzzle is RSA based on? What kind of mathematical puzzle is Diffie-Hellman based on?

Big Integer Decomposition

Solve Discrete Logarithms

3. Please write out the mathematical expressions of RSA encryption and decryption, and point out what is a public key and what is a private key? And can do simple encryption and decryption calculations.

$n=pq$ , where$p,q$ is a large odd prime number, select the integer$e$ , satisfying$1\le e<\varphi \left(n\right)$ ,$\text{gcd}\left(\phi \right(n),e)=1$ , so that$d=e^{-1}\mathrm{mod}\phi \left(n\right)$ .

public key $n,e$ , private key$d$

Encryption: $c=m^e\mathrm{mod}n$

Decryption: $m=c^{d}modn$

4. What are the principles and limitations of RSA in the selection of various parameters? Why?

The modulus is greater than 1024bit, $p,q$ is a large prime number;

$p-1$，$q-1$ has a large prime factor;$p+1$，$q+1$ also has a large prime factor;

$e$ cannot be too small;

$p,The\; q$ distance cannot be too small.

5. What kind of mathematical problem is based on writing the ElGamal cryptosystem? Please write its encryption expression and decryption expression?

Solving the Discrete Logarithm Problem

Public key $b=g^{a}modp$ , private key$\alpha$ , public parameters$p,g$

When encrypting, choose a random number $k$ , and$\text{gcd}(k,p-1)=1$，$c=(y_1,y_2)=(g^k,m{\beta }^k)\mathrm{mod}p$

Decrypt $m=y_2{y}_1^{-}modp$

6. What kind of mathematical problem is ECC public key cryptography based on? Write out the encryption expression and decryption expression using the ECC public key cryptosystem.

Solving the Difficult Problem of Discrete Logarithm on Elliptic Curve ECDLP

7. Write down the ECC-based Diffie-Hellman key exchange protocol.

8. What is the difference in encryption and decryption speed between RSA and ECC public key cryptographic algorithms? Check out the literature comparing encryption and decryption speeds for hardware and software implementations.

9. What are the common attacks on public key cryptography? What are their characteristics?

Chosen Plaintext Attack (CPA)

Chosen Ciphertext Attack (CCA)

Adaptive Chosen Ciphertext Attack (CCA2)

10. Understand China's commercial public key cryptography algorithm SM2.

Based on elliptic curves

Chapter 6 Message Authentication and Hash Functions

1. Please explain the difference between Hash function and encryption function?

Hash function is irreversible, encryption function is reversible

2. What are the properties of the hash function?

(1) Hybrid transformation (2) Anti-collision attack (3) Anti-image attack (4) Practical effectiveness

3. What is message authentication code MAC? How to construct it?

$\text{MAC}$ has a one-way hash function controlled by a key. Its hash value is not only related to the input, but also related to the key. Only the person holding the key can calculate the corresponding hash value.

Construction method $\text{MAC}=C_K\left(M\right)$ Among them,$M$ is a variable length message,$K$ is the key shared by the sender and receiver,$C_K\left(M\right)$ is a fixed-length authenticator

4. How to successfully attack the MAC algorithm without knowing the key? (167 pages)

Exhaustive key, the key length is $k$ , MAC length is$n$ , if$k=a\times n$ , then the average needs$It\; takes\; \alpha$ rounds to find the correct key.

Ways to find collisions (such as XOR)

5. How to use Hash function and block encryption algorithm to construct MAC?

$E_K(H(M))$

6. What is a message detection code (or message digest) MDC? Briefly describe the similarities and differences between MDC and MAC.

MDC is a one-way hash function without key control. Its hash value is only a function of the input string, and anyone can calculate it.

MDC does not have identity authentication function, MAC has identity authentication function

Both MDC and MAC can detect the integrity of received data

7. Familiar with the construction method of iterative hash function.

8. How many digits are the plaintext input packet length, word length, and output length of MD5?

Plaintext packet length: 512b

word length 32b

Output length 128b

9. How many digits are the plaintext input packet length, word length, and output length of SHA-1?

Plaintext packet 512b

word length 32b

Output length 160b

10. Master the basic methods of applying hash functions, and be familiar with the security functions provided by Figure 6-1, Figure 6-2, Figure 6-5, and Figure 6-6.

11. Familiar with the construction of Chinese commercial hash function SM3.

Plaintext packet 512b

word length 32b

Output length 256b

Chapter 7 Digital Signatures

1. What properties should a digital signature have?

(1) The recipient can confirm or verify the issued signature, but cannot forge it

(2) After the sender sends a signed message to the receiver, he can no longer deny the message he signed

(3) The recipient cannot deny that the signed message has been received, that is, there is receipt certification

(4) The third party can confirm the message transmission between the sending and receiving parties, but cannot forge the process

2. What are the types of digital signatures?

deterministic signature, randomized signature

3. What kind of mathematical problem is the RSA signature based on?

Big integer factorization problem

4. What kind of mathematical problem is ElGamal signature based on? Please write down the signature equation of ElGamal.

Solving the Hard Problem of Discrete Logarithms

private $x$，public key$p,g,y\equiv g^x\mathrm{mod}p$

Choose a random number $k$ , satisfy$\text{gcd}(k,p-1)=1$

$r\equiv g^k\mathrm{mod}p$，$s\equiv [H(m)-x\cdot r]\cdot k^{-1}mod(p-1)$

$Si{g}_{sk}(m)=(r,s)$

Verify：$y^r\cdot r^s\equiv g^{H(m)}modp$

5. What is the difference between Schnorr signature and ElGamal signature? Please compare the similarities and differences between the two.

The same point: both are based on solving discrete logarithm puzzles

6. Please write down the signature equation of DSS, and compare its similarities and differences with ElGamal and Schnorr.

Public key $p,q,g,y\equiv g^x\mathrm{mod}p$ , private key$x$

Select random number $k$，$0<k<q$

签名：$Si{g}_{sk}(m)=(r,s)$ , where$r\equiv (g^{k}modp)modq$，$s\equiv [H(m)+x\cdot r]\cdot k^{-1}\mathrm{mod}q$

Verification: Calculate $w\equiv s^{-1}modq$，$u_1\equiv \left[H\right(m)\cdot w]modq$，计算$u_2\equiv r\cdot wmodq$，$v\equiv [(g^{u_1}\cdot y^{u_2})modp]modq$ , correct$\iff v=r$

7. In the above three signature schemes, the user must choose a random number k each time he signs. If the random number k is replaced by a constant, what security issues will arise? Please analyze it.

ElGamal：$H(m_i)=r_i\times x+s_i\times k\mathrm{mod}(p-1)$，$i=1,2$

Schnorr：$s_i\equiv k+x{e}_{i}modq$，$i=1,2$

DSS：$r$相同，$s_i\equiv [k^{-1}(H(m_i)+xr)]modq$，$i=1,2$

Solve the system of equations to obtain the key $x$

8. Can Diffie-Hellman be used for digital signature?

cannot

9. Can the single-key system be used for digital signatures?

cannot

10. Try to compare the difference between digital signature and public key encryption algorithm in the use of key.

Digital signature is signed with the signer's private key and verified with the signer's public key. Double-key encryption means that the sender uses the receiver's public key to encrypt the message, and the receiver uses his own private key to decrypt the message.

11. Please list the digital signature systems with special functions? What are they for?

Undeniable signature, anti-failure signature, blind signature, group signature, proxy signature, designated verifier signature, one-time digital signature

12. Understand the Chinese commercial digital signature algorithm SM2.

Based on solving the discrete logarithm problem on elliptic curves

Chapter 8 Cryptographic Protocols

1. What are the three main features (meanings) that make up the agreement?

Orderliness, steps are executed sequentially

at least two participants

must complete a task

2. What is an arbitration agreement? What is an award agreement? What is a self-executing agreement?

Arbitration agreement: There is a third party trusted by all parties as an arbitrator to help two distrustful entities complete the agreement

Arbitration agreement: a trusted third party does not directly participate in the agreement, and only when a dispute occurs, the adjudicator will execute the agreement

Self-executing protocol: the protocol itself guarantees fairness. If one party in the protocol tries to cheat, the other party can immediately detect the occurrence of cheating and stop the execution of the protocol

3. If classified according to the functions of cryptographic protocols, what types of cryptographic protocols can be divided into?

(1) Key establishment protocol

(2) Authentication Establishment Protocol

(3) Authenticated key establishment protocol

4. What is a man-in-the-middle attack? How to conduct a man-in-the-middle attack on the Diffie-Hellman protocol? Please use drawing to analyze the detailed process of man-in-the-middle attack on the Diffie-Hellman protocol.

Not only is Mallory able to eavesdrop on the messages exchanged between A and B, but he is also able to modify messages, delete messages, and even generate entirely new ones. When B talks to A, M can impersonate B, and when A talks to B, M can pretend to be A.

5. What is the essential reason why the DH protocol cannot resist man-in-the-middle attacks? How to transform the DH protocol to resist man-in-the-middle attacks?

no authentication

Add digital signature, or verify public key certificate

6. Can Diffie-Hellman be used for digital signature?

cannot

7. Master the idea of ​​security protocol design of Big Mouth Frog Protocol, Yahalom, Kerberos protocol.

Big Mouth Frog Protocol: Both A and B share a key with T, and only need to send two messages to send a session key to B.

Yahalom: B first contacts T, and T only sends a message to A.

Kerberos: Both A and B share a key with T, using a time stamp and valid period $L$。

8. Please draw a picture to analyze why the SKID protocol on page 218 cannot resist man-in-the-middle attacks? How to transform this protocol to effectively resist man-in-the-middle attacks?

As shown in the figure above, assume that the middleman knows the key $K$ (otherwise I think it can’t be done), know the key$K$ , the natural middleman is omnipotent, and the topic is quite speechless.

Solution: digital signature, digital certificate.

9. What are the methods of attacking cryptographic protocols?

Known plaintext attack, chosen ciphertext attack, oracle session attack, parallel session attack

10. What are the common methods for security analysis of cryptographic protocols?

Attack testing method, formal language logic proof, provable security analysis

Chapter 9 Digital Certificates and Public Key Infrastructure

1. What is PKI? What parts does PKI consist of? What is the role of each component?

PKI is a standard-compliant infrastructure that provides security services based on public key theory and technology.

PKI consists of certificate authority, registration authority, certificate issuing library, key backup and recovery, certificate revocation, and PKI application interface

(1) The certificate authority (CA) is responsible for issuing and managing digital certificates

(2) The registration authority (RA) reviews the user's qualifications in accordance with specific policies and management specifications, and performs operations such as "whether to agree to issue a certificate to the applicant, revoke the certificate", and bear all consequences caused by review errors

(3) The certificate release database is a public information database available online for open inquiries by the public

(4) Key backup and recovery Provide key backup and recovery mechanism

(5) Certificate revocation warns other users not to use the user's public key certificate

(6) PKI application interface enables users to conveniently use security services such as encryption and digital signature

2. What is a digital certificate? What does a digital certificate contain?

A digital certificate is a combination of a user's identity and the public key it holds. Before the combination, a trusted authority, CA, verifies the user's identity, and then the authority performs a certificate that combines the user's identity and the corresponding public key. Digitally signed to attest to the validity of its certificate.

3. Understand the format of digital certificates stipulated in the X.509 standard.
Version number, certificate serial number, signature algorithm identifier, signer, validity period (before/after), subject name, subject public key information, issuer unique identifier, subject unique identifier, extended information, CA signature.

4. In practice, who will issue the certificate? When issuing a certificate, whose key (private or public) is signing it? When verifying a certificate, whose key is used to verify it?

CA, CA's private key for signature, CA's public key for verification.

5. What is the function of digital certificate? What kind of problems in network security is it essentially solving?

The digital certificate binds the user identity with the public key held, which can prove the relevant information of the network entity in a specific security application

In order to solve the problem of public key credibility

6. In practical applications, if a hierarchical CA architecture is adopted, how to implement digital certificate verification between two users located in different sub-CAs?

Obtain the certificate chain of the certificate to be verified, and obtain the signature of the public key verification certificate of the upper-level certificate in turn until reaching the trusted root node CA

7. What is a cross certificate?

Cross-certificate can allow root CAs of different PKI domains to perform cross-certification, thereby solving different trust problems of root CAs

8. How to realize the revocation of digital certificate? How to implement online query of digital certificates?

Maintain a certificate revocation list (CRL) or implement an online certificate status protocol to check the revocation status of a certificate.

The client sends an online certificate status query request (OCSP Request) to the OCSP responder to check whether the certificate is revoked

The OCSP responder queries the server's X.500 directory to see if a particular certificate is valid

Based on the status check structure looked up, the OCSP responder sends a digitally signed OCSP response to the client

9. What is a roaming certificate? Briefly describe its basic working principle.

Roaming certificates are provided through third-party software that allow users to access their own public-private key pair.

Fundamental:

(1) Store the digital certificate and private key in a secure central server;

(2) When the user needs a digital certificate, he can authenticate himself to the server;

(3) After successful authentication, the server sends the certificate and private key to the user;

(4) When the user finishes the work, the software automatically deletes the certificate and private key.

10. What are the components of a PKI/CA digital certificate system?

Issuing center, key management center, registration system, certificate issuing system, online certificate status query system

Chapter 10 Network Encryption and Key Management

1. What is link encryption? What are the pros and cons?

advantage:

(1) Encryption is transparent to users, and any information sent over the link is encrypted before being sent.
(2) Only one pair of keys is required for each link.
(3) Provides a signal flow security mechanism.

Disadvantage: Data appears in plain text at intermediate nodes, and the cost of maintaining node security is high.

2. What is node encryption? What are the pros and cons?

advantage:

(1) Encryption and decryption of messages are carried out in the security module, which prevents the content of messages from being leaked
(2) Encryption is transparent to users

shortcoming:

(1) Certain information (such as headers and routing information) must be transmitted in clear text
(2) Because all nodes must have keys, key distribution and management become difficult

3. What is end-to-end encryption? What are the pros and cons?

advantage:

(1) Encrypt the entire communication line between two terminals
(2) Only two encryption machines are needed, one at the sending end and one at the receiving end
(3) During the transmission process from the sending end to the receiving end, the message is always Existing in ciphertext
(4) is more secure and reliable than link and node encryption, and easier to design and maintain

Disadvantage: It cannot prevent business flow analysis attacks.

4. What is hybrid encryption? What are the pros and cons?

Hybrid encryption is composed of link and end-to-end hybrid encryption.

Advantages: In terms of cost, flexibility and security, the general end-to-end encryption method is more attractive. For some remote facilities, link encryption may be more appropriate.

Disadvantages: Information security design is more complicated.

5. What is key management? What aspects of management does it include?

Key management deals with issues related to the entire process from key generation to final destruction, including system initialization and key generation, storage, backup/recovery, loading, distribution, protection, update, control, loss, and revocation and destruction etc.

6. What types of keys are there? What are they each for?

(1) The basic key or the initial key is a key selected by the user or assigned by the system, which can be used exclusively by a pair of users for a long period of time. Its purpose is to start and control a key generator constructed by a certain algorithm together with the session key to generate a key stream for encrypting data.

(2) The host master key, which is used to encrypt the key encryption key, is stored in the host processor.

(3) Key encryption key, the key used to encrypt the transmitted session or file key, also known as the secondary primary key, auxiliary key or key transmission key.

(4) The session key is the key used by two communication terminal users when they talk or exchange data.

(5) The data encryption key, also known as the working key, expands the amount of keys that can be used without increasing the workload of key replacement.

7. What are the basic methods of key distribution?

Using Secure Channels to Realize Key Delivery

Establishing Secure Channel Delivery Using Dual Key System

Quantum technology enables key delivery

8. How to verify the correctness of the key injection when using the key gun to inject the key?

(1) The key gun will be a random number $R_N$inject secret machine

(2) The master key $K_m$Encryption: $E_{K_m}(R_N)$

(3) Calculation of $K_m$The hash function value of : $h(K_m)$

(4) The secret machine will be $E_{K_m}\left(R_N\right)$ and$h\left(K_m\right)$ looped back to the keygun

(5) Key gun inspection $h\left(K_m\right)$ value, and check the decrypted$R_N$

9. Why should keys be divided into different levels in key management?

Ensure that very few keys are stored in plain text in the host encryption device with strict physical protection, and other keys are stored in encrypted cipher text in the memory outside the cipher, thus greatly simplifying key management and Enhanced key security.

10. What parts does a key management system consist of? (This question was not found)

Key generation, key storage, key backup and recovery, key update, key destruction and revocation.

11. What are the four stages of the lifetime of the key? Learn the 12 working steps of key management.

four stages:

(1) Pre-operation stage

(2) Operation stage

(3) Post-operation stage

(4) Scrapping stage

12 working steps: user registration, user initialization, key generation, key input, key registration, normal use, key backup, key update, key file, key cancellation and destruction, key recovery, key revoke

12. Find information to know what mathematical properties a good key should have?

(1) Truly random, equal probability

(2) Avoid using weak keys for specific algorithms

(3) Satisfy a certain mathematical relationship

(4) Easy to remember but hard to guess

(5) Use key kneading or hash technology to transform long, easy-to-remember sentences into pseudo-random number strings through a one-way hash function

Chapter 11 Wireless Network Security

1. What are the major security threats to wireless networks? It is necessary to be able to identify which are active attacks and which are passive attacks.

Passive attack: eavesdropping, service area identifier disclosure

Active attacks: communication blocking, data injection and tampering, man-in-the-middle attacks, client impersonation, access point masquerading, anonymous attacks, client-to-client attacks, wireless channel concealment, and replay attacks.

2. What are the main security flaws in the GSM system?

Leaking IMSI information when booting for the first time may lead to user identity disclosure

The base station implements one-way authentication for the user. The fake base station sends fraudulent information to the user.

Backbone network data transmission without encryption intermediate nodes can intercept the session key

No data integrity verification mechanism cannot detect whether data has been tampered with

K's direct participation in authentication and encryption has the risk of leaking the master key

The master key K exists in the SIM card and there is a risk of duplicating the SIM card

3. What security functions does the 3G system have? What are the major security flaws? Compared with 2G, what security improvements have been made in 3G?

Realized two-way authentication between user networks, established a session key between user networks, kept the freshness of the session key, and added data integrity verification function

defect:

Leaking IMSI information when booting for the first time may lead to user identity disclosure

Backbone network data transmission without encryption intermediate nodes can intercept the session key

K directly participates in the authentication and encryption master key lacks hierarchical protection

$CK$和I IThere is a risk of eavesdropping on$IK$$direct\; transmission$

The master key K exists in the SIM card and there is a risk of duplicating the SIM card

Using 10 security algorithms $f_1\sim f_{10}$There is a risk of being compromised if there are too many algorithms

4. What security functions does the 4G system have? What are the major security flaws? What security improvements have been made in 4G compared to 3G?

It realizes two-way authentication between user networks, establishes session keys between user networks, increases data integrity verification, realizes hierarchical key management, and hides the encryption key CK $CK$ and integrity verification key$IK$

defect:

Leaking IMSI information when booting for the first time may lead to user identity disclosure

Backbone network data transmission without encryption intermediate nodes can intercept the session key

The improvements and features are as follows:

5. Please draw a diagram to analyze the working process of the GSM cellular system security and authentication protocol, and point out the security function played by each element in the triplet authentication vector.

Triple Authentication Vector

$\text{RAND}$ : used for user authentication and session key generation

$\text{SRES'}$ : Used for the authentication response$\text{SRES}$ comparison

$K_c$: session key, used to encrypt data

6. Please draw a diagram to analyze the working process of the 3G cellular system security and authentication protocol, and point out the security function played by each element in the quintuple authentication vector.

$\text{RAND}$ : used for user and network two-way authentication and session key generation

$XRES$ : Used for network authentication of users

$CK$ : data encryption key

$IK$ : integrity verification key

$\text{AUTN}$ : Used to authenticate users to the network

7. Why is the challenge value RAND of the 2G/3G/4G system a random number instead of a constant? If the challenge value RAND is constant, what kind of security issues will arise? Please analyze it.

Constants have security issues, and random numbers keep keys fresh. The challenge value is a random number that can prevent brute force attacks. A 128b random number means $3.4\times 10^{With\; 38}$ possible combinations, even if a hacker knows the A3 algorithm, the probability of guessing a valid RAND/SRES is very small.

Replay attacks, compromise of session keys, device camouflage, etc.

8. Compared with 2G/3G/4G, in what ways does 5G improve security?

Increased user identity protection, realized two-way authentication between user networks, established session keys and data integrity verification keys between user networks, realized hierarchical key management, and hidden encryption keys CK $CK$ and integrity verification key$IK$

write at the end

It is also the first time for the author to write an article on CSDN, and I don’t know much about the original format, so please bear with me~ I wish you all a smooth exam! !