Cryptography and Protection
Cryptography converts readable data (plaintext) into unreadable data (ciphertext) using a key. Encryption is plaintext to ciphertext; decryption is the reverse.
| Type | Keys | Facts |
|---|---|---|
| Symmetric | One shared key for both | Fast. Key distribution is the problem. AES, DES, 3DES. |
| Asymmetric (public key) | Public key encrypts, private key decrypts | Slower but safe to share the public key. RSA. |
| Hashing | No key; one-way | Fixed-size fingerprint of data. Checks integrity. MD5, SHA-256. |
- Digital signature: the sender signs with the private key; anyone verifies with the public key. It proves who sent it and that it was not changed. Legally valid under the IT Act.
- Digital certificate: issued by a Certificate Authority (CA); links a public key to an identity.
- SSL/TLS: encrypts the connection between browser and site (HTTPS, padlock icon).
- Steganography: hiding a message inside an image or other file.
Protective measures
| Measure | What it does |
|---|---|
| Firewall | Filters incoming and outgoing traffic by rules. Hardware or software. |
| Antivirus | Detects and removes malware. Needs regular signature updates. |
| IDS / IPS | Intrusion Detection / Prevention System. |
| VPN | Encrypted tunnel for safe browsing. |
| 2FA / MFA | Two-factor or multi-factor login: password + OTP, fingerprint or token. |
| OTP | One-Time Password, valid for one use. |
| CAPTCHA | Test to separate humans from bots. |
| Backup | Extra copy of data. Good practice is the 3-2-1 rule: 3 copies, 2 media, 1 off-site. |
| Software updates (patches) | Close known security holes. |
Safe practices
- Use long, unique passwords (12 or more characters, mixed). Never share your OTP, PIN or CVV.
- Do not open attachments or links from unknown senders. Check for https before entering card data.
- Do not use public Wi-Fi for banking.
Keep practising
Notes are only half the work. Test yourself with questions and discuss doubts with other aspirants.
Prepared for exam revision from standard computer textbooks, Microsoft documentation and official sources. Features differ between Excel and Word versions (2016, 2019, 2021, 365) so check which version your exam follows. Found a mistake? Tell us.