Describe encryption methods (symmetric, asymmetric)

1. Data Processing and Information – Encryption Methods

Symmetric Encryption 🔒🔑

Symmetric encryption uses the same key for both encrypting and decrypting data. Think of it like a secret diary where you and your best friend share a single key (the diary’s lock). Only you two can read the notes because you both know the key. This method is fast and works well for large amounts of data.

• Single key for both encryption and decryption.
• Very fast – ideal for big files or streaming.
• Key must be shared securely (e.g., face‑to‑face, secure channel).
• Common algorithms: AES, DES, 3DES.

The encryption process can be written simply as:

$$C = E_K(P)$$

Where P is the plaintext, C the ciphertext, and K the shared key. The same K is used to recover P from C.

Asymmetric Encryption 🗝️📬

Asymmetric encryption uses a pair of keys: a public key that anyone can see, and a private key that only the owner keeps. Imagine a mailbox with a lock that anyone can lock (public key) but only you can unlock (private key). This solves the problem of key distribution – you never have to send the private key anywhere.

1. Generate a key pair: (public, private).
2. Share the public key openly (e.g., on a website).
3. Encrypt data with the public key.
4. Decrypt data with the private key.

Key generation often involves large prime numbers. For RSA, the math looks like this:

$$C = M^e \bmod n$$

Where M is the message, e the public exponent, and n the modulus (product of two primes). The private key uses the exponent d to recover M.

Another popular asymmetric method is Diffie‑Hellman key exchange, which lets two parties agree on a shared secret over an insecure channel:

$$g^{ab} \bmod p$$

Here, g is a base, a and b are private exponents, and p is a large prime. Both parties compute the same value g^{ab} mod p, which becomes a shared secret key.

Comparison Table 📊