← VCE Data Analytics U4O2

Choosing a cryptographic technique for a scenario

Choose symmetric encryption for stored data, asymmetric keys to swap keys and sign, and hashing to check integrity and store passwords. Justify the choice.

Part of: VCE Data Analytics - U4O2 - Cyber Security: Data Security — Module 78, ACARA Digital Technologies Years 9–10 — Cyber Security Threats and Vulnerabilities — Module 151, QCE Digital Solutions Unit 4 — Digital Methods for Exchanging Data — Module 51

Understanding Choosing a cryptographic technique for a scenario in VCE Data Analytics U4O2

What it does: ECDH uses asymmetric key pairs to let both sides work out a shared secret key. That key then drives fast symmetric encryption for data in transit. A salted hash is one-way, so the original password cannot be recovered. The site hashes the login attempt and compares it to the stored value. Asymmetric techniques let two parties establish a shared key over an open network. A hash of the key cannot be reversed, so the receiver could not use it. Hashing supports integrity. If even one bit changes, the hash changes. Encrypting a file does not show whether it was altered.

Common mistakes: Symmetric encryption like AES uses one shared secret key to both encrypt and decrypt. A public/private pair belongs to asymmetric encryption. The line should be key = "one shared secret key". Checking that a file is unchanged is an integrity job, so you compare hashes. Encryption protects confidentiality and does not provide a digest to compare. It should be technique = "hash (SHA-256)".

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This module's key terms are also in a printable crossword (Modules 44–79) and word search (Modules 44–113).

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Learning

Duo

A school stores student records on a server hard drive. Which technique best protects the data at rest?

Hashing the recordsSymmetric encryption such as AES

Matches

Store customer passwords using AES encryption

↓

Passwords should be hashed (and salted), not encrypted. Encryption can be reversed with the key, so a thief who steals the key can read every password.

Applying

Meanings

Term

Match technique to job

Meaning

Choose symmetric encryption for stored data, asymmetric keys to swap keys and sign, and hashing to check integrity and store passwords. Justify the choice.

Practice

Stored files: use AES (symmetric) - fast and keeps data confidential

Testing

Gaps

technique ← " encryption"

Check Answer

Spots

3technique = "AES symmetric"

4key = "public/private pair"

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Quick Questions

1. A school stores student records on a server hard drive. Which technique best protects the data at rest?

A. Hashing the records

B. Symmetric encryption such as AES ✓

Stored data must be readable again by authorised users. Symmetric encryption is fast and reversible, so it suits data at rest. A hash is one-way and cannot be turned back into the records.

2. Two computers must agree on a secret key over the internet without anyone intercepting it. Which technique is used?

A. Hashing the key and sending the hash

B. Asymmetric key exchange such as ECDH ✓

Asymmetric techniques let two parties establish a shared key over an open network. A hash of the key cannot be reversed, so the receiver could not use it.

3. You download a file and want to check it has not been altered. What should you do?

A. Hash the file and compare it with the published hash ✓

B. Encrypt the file with a Caesar cipher

Hashing supports integrity. If even one bit changes, the hash changes. Encrypting a file does not show whether it was altered.

4. A website needs to store user passwords in its database. Which is the better choice?

A. Store a salted hash of each password ✓

B. Encrypt passwords so staff can decrypt and read them

Hashing is one-way, so a stolen database does not reveal passwords. Salting stops identical passwords from giving identical hashes. Reversible encryption lets an attacker with the key read every password.

5. You must prove an email really came from a particular sender. Which technique fits?

A. A digital signature using the sender's private key (e.g. ECDSA) ✓

B. Encrypting the email with a symmetric key both people share

Only the sender holds the private key, and anyone can check the signature with the public key. A shared symmetric key could have been used by either person, so it cannot prove who sent it.

Match the Pairs

AES-256 encrypt the database file → Symmetric encryption protects stored (at rest) data so only people with the key can read it, keeping it confidential.

SHA-256 hash of the downloaded file → A hash gives a fixed-length fingerprint, so you can check the file has not been changed (integrity).

Two strangers need to agree on a shared key over the internet without sending the key itself, so they use asymmetric key exchange. → ECDH key exchange

A website stores user passwords so that a breach does not reveal them, and it still needs to check a login. It uses a salted hash. → stored = hash(salt + password)

Store customer passwords using AES encryption → Passwords should be hashed (and salted), not encrypted. Encryption can be reversed with the key, so a thief who steals the key can read every password.

Use a hash to keep a file secret from outsiders → Hashing does not protect confidentiality because the data cannot be recovered from the hash. Use encryption to keep a file secret and a hash to check integrity.

Key Term

Match technique to job

Choose symmetric encryption for stored data, asymmetric keys to swap keys and sign, and hashing to check integrity and store passwords. Justify the choice.

Fill in the Blanks

1. IF job = "stored data" THEN technique ← "symmetric encryption" END IF

Hint: Type the kind of encryption that uses one shared key and suits data at rest.

2. IF job = "swap keys" THEN technique ← "asymmetric keys" END IF

Hint: Type the kind of encryption that uses a public and private key pair to exchange keys safely.

3. IF job = "check integrity" THEN technique ← "hashing" END IF

Hint: Type the technique that makes a fixed-length digest to show data has not changed.

4. stored ← hash(password + salt) SAVE stored TO database

Hint: Type the function name that turns a salted password into a one-way digest for safe storage.

5. IF goal = "integrity" THEN technique ← "hashing" END IF

Hint: Type the security goal that means data has not been altered, which a hash can check.

Spot the Error

Question 1

A job = "customer data at rest"

B need = "confidentiality"

C technique = "AES symmetric"

D key = "public/private pair"

Line D — Symmetric encryption like AES uses one shared secret key to both encrypt and decrypt. A public/private pair belongs to asymmetric encryption. The line should be key = "one shared secret key".

Question 2

A job = "check file unchanged"

B need = "integrity"

C technique = "AES encryption"

Line C — Checking that a file is unchanged is an integrity job, so you compare hashes. Encryption protects confidentiality and does not provide a digest to compare. It should be technique = "hash (SHA-256)".

Question 3

A job = "store user passwords"

B need = "protect if DB leaked"

C technique = "hash with salt"

D store = encrypt(pw, key)

Line D — Passwords should be stored as salted hashes, which cannot be reversed. Encrypted passwords can be decrypted if the key is stolen. The line should be store = hash(salt + pw).

Question 4

A job = "share a key over Wi-Fi"

B technique = "hash (SHA-256)"

C need = "secure in transit"

Line B — Swapping a key safely over an open network needs asymmetric methods such as ECDH or RSA. A hash is one-way and cannot be used to exchange a key. It should be technique = "asymmetric (ECDH)".

Question 5

A job = "sign a document"

B need = "prove who sent it"

C use = "public key to sign"

Line C — A digital signature is created with the sender's private key, which only they hold. Anyone then checks it with the public key. The line should be use = "private key to sign".

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