Using a certain rule, I can express "THIS PHRASE IS VALID" as "KZZK GZISKV ZK PSDZV". What is this rule, and how did I come to it?

Hint/Note: Non-native English speakers may have a more difficult time solving this.

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    $\begingroup$ Do you plan to change your username every time you post a new puzzle? $\endgroup$ Apr 8 '20 at 23:14

This is a

Vigenere cipher

With the key


Which decides the cipher text to the required ‘THIS PHRASE IS VALID’

The actual intended solution was:

Each letter had been rotated through the alphabet using ROT X where X is the number of keys on the particular row a letter is on. X can be rot 10, 9 or 7.

This has the same affect as using the key above, as vigenere uses the letter to rotate a certain amount of characters.

  • $\begingroup$ Truth be told, I did not intend for it to be solved as you have done above. I used a more manual approach to reach the key I used. If you can solve that, I will be very impressed. The answer might even be right under your nose. $\endgroup$ Apr 8 '20 at 18:59
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    $\begingroup$ Literally any plaintext could be sent to any ciphertext with some meaningless Vigenere key. I'm tempted to downvote or flag as NaA: it's essentially subtracting one sequence of letters from the other to get another meaningless string, which doesn't really make sense as an encryption method without some justification. $\endgroup$ Apr 8 '20 at 19:30
  • $\begingroup$ I did not intend for it to be a Vigenere cipher. A key point might be that there are only three rots for the entire sequence. The entire alphabet would be expressed as "S V W V V X Y Z Z B C D G H F G H I K K L P N R P T". There is something, almost certainly right in front of you, that you can use to determine why these three specific rots are used. That is what I was looking for, I apologize if I was unclear or too vague. $\endgroup$ Apr 8 '20 at 19:40
  • $\begingroup$ @Randal'Thor this is still an answer, and it’s still correct, it’s just not the intended answer. As the key has three different letter it is still using the three rotations the OP used, just in a single go $\endgroup$ Apr 8 '20 at 19:44
  • $\begingroup$ @First-TimePuzzlePoster this particular vigenere key does use the three rotations you are looking for, just at once. I’m still not sure why the rotations are in this particular order however $\endgroup$ Apr 8 '20 at 19:46

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