One-Time Pad Generator

What the One-Time Pad Does

The one-time pad (OTP) is the only cipher with mathematically proven perfect secrecy. This tool generates a random key and XORs it against your plaintext: each plaintext bit is combined with a key bit, producing ciphertext that — absent the key — is consistent with every possible message of the same length.

Why It Is Unbreakable (Under Strict Rules)

Claude Shannon proved that XOR with a truly random key as long as the message leaks zero information about the plaintext. But that proof rests on three conditions, and breaking any one collapses the security:

• The key must be truly random. A key from a predictable pseudo-random generator is only as strong as that generator — it is no longer information-theoretically secure.
• The key must be as long as the message. Stretching a short key (repeating it) turns the OTP into a Vigenère cipher, which falls to frequency analysis.
• The key must never be reused. Reuse is the classic, fatal mistake: XOR two ciphertexts encrypted with the same key and the keys cancel, leaving the two plaintexts XORed together — often enough to recover both.

That is why it is a one-time pad.

The Practical Catch

OTP is provably secure but rarely practical: you must securely distribute as much truly random key material as you will ever send. Key distribution is the hard part — if you can move a long secret key safely, you could often just move the message. This is why modern systems use shorter keys with algorithms like AES instead.

When to Use It

• Teaching perfect secrecy and the role of randomness and key reuse.
• CTF and puzzle work involving XOR.
• Understanding why "unbreakable" depends entirely on operational discipline.

Key generation and XOR run entirely in your browser — your plaintext and key are never uploaded.