Security measures and protecting data
| English | Chinese | Pinyin |
|---|---|---|
| public key | 公钥 | gōng yào |
| private key | 私钥 | sī yào |
| antivirus | 杀毒软件 | shā dú ruǎn jiàn |
| backup | 备份 | bèi fèn |
| encryption | 加密 | jiā mì |
| firewall | 防火墙 | fáng huǒ qiáng |
| user accounts | 用户账户 | yòng hù zhàng hù |
| audit logs | 审计日志 | shěn jì rì zhì |
| anti-spyware | 反间谍软件 | fǎn jiàn dié ruǎn jiàn |
| access rights | 访问权限 | fǎng wèn quán xiàn |
| authentication | 身份验证 | shēn fèn yàn zhèng |
| biometrics | 生物识别 | shēng wù shí bié |
| two-factor authentication | 双因素认证 | shuāng yīn sù rèn zhèng |
| authorisation | 授权 | shòu quán |
| VPN | 虚拟专用网 | xū nǐ zhuān yòng wǎng |
| ciphertext | 密文 | mì wén |
| least-privilege | 最小权限 | zuì xiǎo quán xiàn |
| plaintext | 明文 | míng wén |
| symmetric encryption | 对称加密 | duì chèn jiā mì |
| asymmetric encryption | 非对称加密 | fēi duì chèn jiā mì |
| digital signature | 数字签名 | shù zì qiān míng |
A lock anyone can close and only one person can open
- Every time you pay online, your card number crosses dozens of routers owned by strangers. Any of them could copy the bytes.
- What makes it safe is an idea from 1977: a lock that anyone can snap shut but only the holder of one particular key can open. You lock your card number with the shop's public key; only the shop's private key opens it.
- That is one measure among many. This lesson is the defences, from a single PC to the open internet, how each one works in the words the examiner awards, and which one fits which threat.
A standalone PC
- A strong password: long, mixed characters, changed regularly, never shared.
- Antivirus 杀毒软件 kept up to date, prompt software updates, and a locked screen when you step away.
- A backup 备份 to separate media, kept off-site, so lost or corrupted data can be restored; full-disk encryption 加密 so a stolen laptop gives up nothing.
Which measures protect a standalone PC that is never networked? Select all that apply.
Malware still arrives on USB sticks and downloads, and disks still fail, so password, antivirus and backups apply. Network log-in auditing is a networked-PC measure.
A networked PC
- Everything above, plus a firewall 防火墙: it examines every incoming and outgoing transmission, compares it with set criteria such as a whitelist or blacklist of addresses, ports and protocols, blocks any that do not meet the criteria, and can warn of unauthorised access attempts.
- Central user accounts 用户账户 with per-user permissions: admin rights only for admins.
- Audit logs 审计日志 record who logged in and what they touched.
Traffic that fails the criteria never reaches the computer
A firewall mainly:
A firewall controls which network traffic is allowed in or out, by a set of rules.
How the measures work, in the examiner's words
- Anti-virus and anti-spyware 反间谍软件 software scans files and programs against a database of known malware signatures, checks behaviour, quarantines or deletes what it finds, and must be updated so new malware is recognised.
- Passwords and user accounts: only a user who knows the password can log in; accounts lock after repeated failures; each account carries its own access rights.
- Access rights 访问权限: each user or group gets permissions for each file or table, such as read-only or read and write, so nobody sees or changes data that is not theirs.
- Backups: a copy on separate media, off-site, from which lost data is restored.
Authentication
- Authentication 身份验证 verifies who the user is: something they know (a password), something they have (a token or phone), or something they are (biometrics 生物识别).
- Biometrics: the device captures the face, fingerprint or iris, converts it to digital data, compares it with the stored data for that user and allows access only on a match. It cannot be forgotten, lent or guessed.
- Two-factor authentication 双因素认证 combines two factors, so a stolen password alone is not enough. Authorisation 授权 then decides what the verified user may do.
Something you have
Something you are
A code from a phone app is an example of which authentication factor?
A token/phone code is "something you have". Two-factor combines it with a password ("know") or biometric ("are").
A fingerprint reader authenticates a user by something they ____.
Know (password), have (token), are (biometric feature). A biometric cannot be forgotten, lent or guessed.
Matching the measure to the threat
- Interception in transit: encrypt the data (HTTPS, a VPN 虚拟专用网). Intercepted ciphertext is useless without the key.
- Unauthorised access: strong authentication and two-factor, lock-out after failed logins. Internal misuse: the least-privilege 最小权限 principle, each user gets only what they need, plus auditing.
- Malware: anti-virus and anti-spyware with real-time scanning, and patching. Phishing: user training, email filtering, check the URL. DDoS: rate limiting and traffic filtering.
Match each threat to the security measure that best counters it.
Each threat has a best-fit defence — encrypt against interception, authenticate against intruders, patch against malware, limit privilege against insiders.
The best defence against data being intercepted in transit is to:
Encrypted data intercepted in transit is useless without the key. Authentication and antivirus address different threats.
Encryption
- Encryption scrambles plaintext 明文 with a key into ciphertext 密文, so an intercepted copy cannot be understood without the key; the receiver uses a key to decrypt it. It protects data in transmission and in storage.
- Symmetric encryption 对称加密 (AES) uses one shared key to encrypt and decrypt: fast, but the key itself must reach the receiver safely.
- Asymmetric encryption 非对称加密 (RSA) uses a public key 公钥 to encrypt and the matching private key 私钥 to decrypt. The public key can be given to anyone, which solves the key-sharing problem.
One shared key, or a public key to lock and a private key to unlock
Encrypt with a Caesar cipher
Change the shift — that is the key. Each letter slides that many places along the alphabet to make the ciphertext, and the same key slides it back. That shared key is symmetric encryption in miniature.
Asymmetric encryption (e.g. RSA) differs from symmetric (e.g. AES) because it:
Asymmetric uses a public/private key pair (solving key sharing); symmetric uses one shared key (fast).
Put symmetric encryption in order, from sender to receiver.
Symmetric encryption uses one shared key both to lock (encrypt) and unlock (decrypt) — anyone intercepting the ciphertext can't read it without that key.
Symmetric encryption uses one shared key, while asymmetric encryption uses a public key to encrypt and a private key to decrypt.
That public/private split is what lets asymmetric encryption solve the problem of sharing a key safely.
Worked example: how a digital signature authenticates a document
- Explain how a digital signature is used to authenticate a document. [5]
- The sender puts the message through a hash function to produce a digest. The sender encrypts the digest with their private key; that encrypted digest is the digital signature 数字签名.
- The message and the signature are sent together. The receiver decrypts the signature with the sender's public key to recover the digest.
- The receiver hashes the received message and compares the two digests. A match proves who sent it (only the private key could have made the signature) and that it was not altered (any change would alter the hash).
Sign the hash, not the message
Put the steps of sending and checking a digital signature in order.
Hash, sign with the private key, send, unlock with the public key, compare. A match proves the sender and that nothing changed.
Worked example: confidential data crossing the internet
- A company sends confidential data to a branch over the internet. Describe a method to keep it secure. [3]
- Encryption: the data is encoded with a key into ciphertext, so an unauthorised person who intercepts it cannot read it, and only the intended receiver, who has the key, can decode it.
- The same answer covers a program file emailed to a tester: encrypt the file or send it over an encrypted connection, with a password sent separately.
- Say what encryption does and does not do: it stops the data being read, not being intercepted or deleted.
Worked example: access rights in a database
- Describe how access rights protect the data in a database. [3]
- Each user is given an account with a username and password. The database administrator assigns each account permissions for each table: read-only, read and write, or no access.
- Users see only the tables and fields they are allowed to, so a customer cannot open the staff table and a clerk can read but not change the prices. The DBMS enforces this on every query.
With access rights, a clerk can be given permission to read the prices table but not to change it.
Permissions are set per account and per table: read-only, read and write, or no access. The DBMS enforces them on every query.
Marks that slip away
- Encryption protects confidentiality, not integrity. Use a checksum, parity or a check digit for integrity.
- Encryption does not stop interception or deletion; it stops the intercepted copy being read.
- A digital signature encrypts the hash of the message with the private key, not the message itself.
- Name the measure and how it works. "Firewall" alone earns nothing; "compares traffic with set criteria and blocks what fails" does.
You've got it
- layer the defences: password, antivirus, updates, backup, encryption → plus firewall, user accounts, access rights, audit logs → plus VPN, HTTPS, digital signatures
- authentication is something you know / have / are; 2FA combines two; biometrics compares a captured feature with stored data
- match measure to threat: interception → encryption; unauthorised access → authentication; internal → least privilege; malware → anti-virus and patching
- symmetric = one shared key; asymmetric = public key encrypts, private key decrypts; a digital signature is the hash encrypted with the private key