Encryption and Digital Signatures

This lesson covers how data is protected during storage and transmission using encryption. At A-Level you must understand symmetric and asymmetric encryption, the role of keys, and how digital signatures and digital certificates ensure authenticity and integrity.

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What Is Encryption?

Encryption is the process of converting plaintext (readable data) into ciphertext (unreadable scrambled data) using an algorithm and a key. Only someone with the correct key can decrypt the ciphertext back to plaintext.

Plaintext ──→ [Encryption Algorithm + Key] ──→ Ciphertext
Ciphertext ──→ [Decryption Algorithm + Key] ──→ Plaintext

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Symmetric Encryption

In symmetric encryption, the same key is used for both encryption and decryption. Both the sender and receiver must share this secret key.

Sender                                     Receiver
Plaintext ──→ [Encrypt with Key K] ──→ Ciphertext ──→ [Decrypt with Key K] ──→ Plaintext

Examples

• AES (Advanced Encryption Standard) — the most widely used symmetric cipher (128, 192, or 256-bit keys).
• DES (Data Encryption Standard) — older, now considered insecure (56-bit key).
• 3DES (Triple DES) — applies DES three times for stronger security.

Advantages