Encryption & Ciphers

Explore classical and modern encryption methods with step-by-step working. Covers everything on the GCSE and A-Level specs.

Caesar Cipher

Plaintext / Ciphertext

Shift: 3

Caesar cipher: Each letter is shifted by a fixed number of positions in the alphabet. A shift of 13 is called ROT-13. Non-alphabet characters are left unchanged. It is a symmetric cipher; the same key decrypts as encrypts (use shift 26-n to decrypt).

Output

Letter Mapping

Run to see mapping.

Vigenère Cipher

Plaintext / Ciphertext

Key (letters only)

Vigenère cipher: Each letter is shifted by the corresponding letter of a repeating key. Much harder to crack than Caesar since different letters can encrypt to the same ciphertext letter. Key is repeated to match the message length.

Output

Step-by-Step Working

Run to see working.

Vernam Cipher (One-Time Pad)

Plaintext / Ciphertext (letters only)

Key (same length as message)

Vernam cipher: Each letter is XORed with the corresponding key letter. The key must be: the same length as the message, truly random, and used only once. It is theoretically unbreakable; without the key, every plaintext is equally likely.

Output

XOR Working (bit by bit)

Run to see XOR table.

RSA Key Generation

Prime p

Prime q

Public exponent e

Message M (integer, must be < n)

RSA uses small primes here for clarity. Real RSA uses primes with hundreds of digits. The security comes from the difficulty of factoring n = p×q.

Select p and q to begin.