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As an example, even if your cipher is somehow secure against a ciphertext-only attack (it's not), is it secure if I can trick you into encrypting a message for me? What if I can trick you into decrypting a message for me? What if I know part of or all of one of the messages you send? What if you encrypt multiple messages with the same key?

So here's your first envelope. Given a paragraph or two of ciphertext, your cipher will fail to language-based frequency analysis.

As an example, even if your cipher is somehow secure against a ciphertext-only attack (it's not), is it secure if I can trick you into encrypting a message of my choosing? What if I can trick you into decrypting a message of my choosing? What if I know part of or all of the plaintext for a particular encrypted message you've sent? What if you encrypt multiple messages with the same key? What if I can do any or all of these things hundreds or even millions of times in a row? These are all situations that are extremely common in the real world, and under which modern ciphers remain completely secure.

So here's your first envelope: given a paragraph or two of ciphertext, your cipher will fail to language-based frequency analysis.

Your question, MikeAzo's comment

Schneier's law is something to the effect of anyone can create a cipher that they themselves cannot break. For example, your method listed in your question you say results in "completely unreadable" ciphertexts. Unfortunately it is fatally flawed. It would be easy for me to break.

and your reply

@mikeazo: How can you break it if I send you this "QTCPIGXKUXTGG" ciphertext encrypted by a merely a simple algorithm which you have no idea about how it was encrypted?

practically could not be a better example of Schneier's law in practice.

  Schneier stated:

Your question, MikeAzo's comment, and your reply practically could not be a better example of Schneier's Law in practice. Schneier stated:

Your question, Mike Azo's comment, and your reply practically could not be a better example of Schneier's law in practice.

You replied,

Your question, MikeAzo's comment

Schneier's law is something to the effect of anyone can create a cipher that they themselves cannot break. For example, your method listed in your question you say results in "completely unreadable" ciphertexts. Unfortunately it is fatally flawed. It would be easy for me to break.

and your reply

@mikeazo: How can you break it if I send you this "QTCPIGXKUXTGG" ciphertext encrypted by a merely a simple algorithm which you have no idea about how it was encrypted?

practically could not be a better example of Schneier's law in practice.

Schneier stated:

To answer your reply