I came across the following question and it is confusing me.
I'm completely new to cryptography, so please excuse the beginners question.
"Having just completed a course in Cryptography, Tom and Jerry start a new business to manufacture and market cryptography products. Tom designs an encryption algorithm $E_k(m)$ which produces a ciphertext upon encrypting message m with a key k and keeps the algorithm a secret, but the length of $E_k(m)$ is made public. Then Jerry enthusiastically advises Tom to increase the security by constructing $(E_k(m)\oplus m) \Vert (E_k(m)\oplus 1111…11)$ as the final ciphertext.
Here $ \vert\vert $ is the concatenation symbol and $\oplus$ is the XOR operator.
Is this a good scheme?"
Initially at first glance I can see that the new algorithm is more secure, but I couldn't actually get any ciphertext from the equation. Does that make it secure? or does it make it useless because there isn't any ciphertext to decrypt? OR is there ciphertext and I have just tackled it the wrong way?
I am probably going to kick myself, I'm probably missing the entire point.
I really appreciate any help!
