Caesar cipher brute force solver
Solve Caesar cipher puzzles when you do not know the shift. It also shows why this puzzle cipher offers no real security.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter encoded text.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
For each shift k from 1 to 25: original = (y - k) mod 26. Candidates are ranked by how many common English words they contain (the, and, is and so on); ties go to the smaller shift.
Example
Result: Likely shift: 3.
Wkh txlfn eurzq ira mxpsv ryhu wkh odcb grj
The quick brown fox jumps over the lazy dog
Limits and caveats
- This is a puzzle and teaching cipher that is easy to break, so never use it to protect passwords or sensitive data.
- The suggestion relies on common English words, so it can miss on very short or non-English text; check the table.
- The table shows the first 300 characters of each shift.
Questions about this tool
How does it pick the likely shift?
It counts common English words such as the, is and and in each candidate and suggests the shift with the most.
Why only 25 shifts?
A shift of 26 brings every letter back to itself, so there are only 25 different keys.
Can it solve ROT13?
Yes. ROT13 is a Caesar cipher with shift 13, so it appears in row 13 of the table.