Instructions:

Enter an integer less than 256 in the top textfield labeled "Key." Enter a plaintext sentence in the textfield labeled "Plaintext" then hit return. The key is used to scramble the plaintext by xor-ing with all its bytes. The scrambled result is shown in the textfield labeled "Ciphertext." The key is used again in exactly the same way to unscramble the ciphertext. The result is shown in the textfield labeled "Decrypted."

Discussion:

xoring a plaintext message with a random string of 1s and 0s is the least breakable encryption scheme in that no method for determining the string used is any better than brute force which, by itself, cannot be accomplished in real-time. It is possible to generate a pseudo-random string as long as both parties know the algorithm and the seed. In this cipher, though, the same short string of 8 bits is used to encrypt each plaintext byte.

Question:

What major weakness does this approach to encryption/decryption have?