Columnar transposition cipher

All characters move together—spaces, digits, and punctuation keep their places in the sequence and are never stripped—so phrases and CTF payloads stay faithful to textbook worksheets. Use it free in the browser for history-of-crypto lessons, puzzle design, and reversible lab demos, or call the API at $0.002 per successful request when pipelines need reproducible columnar transforms.

What columnar transposition is and what this tool returns

The JSON response includes result for the rearranged string, encoding fixed to columnar, mode set to encrypt or decrypt, key echoing the keyword you supplied, key_length, column_order as the zero-based original indices in read order, input_length and output_length which always match because the transform only permutes, and a formula string that restates the row-write column-read contract for documentation and tests. There is no streaming path and no silent fallback to Vigenère or Base64: either you supply non-empty text and a non-empty key, or the request fails with invalid_input. If you need polyalphabetic shifts, Morse, or modern encryption, use those dedicated endpoints; this landing answers only the classical columnar keyword contract that crypto history chapters and CTF warm-ups already describe.

How text, key, and mode are read and how results stay reproducible

Key accepts keyword, k, password, and passphrase; the entire non-empty string defines the columns, including digits and symbols if you include them, because ordering uses Unicode character comparison rather than stripping to A–Z only. The preferred payload fields are text for the message, key for the keyword, and optional mode for encrypt or decrypt. Text accepts aliases such as input, value, s, message, plaintext, and ciphertext so forms and SDK clients can reuse existing column names without renaming every call site. An empty key or a missing key is rejected with invalid_input and a clear message that a non-empty keyword is required to order the columns. Mode defaults to encrypt when omitted and also accepts short aliases such as enc, encode, e for encrypt and dec, decode, d for decrypt; any other string fails validation. Missing text, empty text, non-string types, and unknown modes all raise invalid_input so a blank form does not look like a successful no-op. Column order is computed once from the key, then the same heights formula is used on encrypt and decrypt so a round trip always restores the original payload for any non-empty string under that keyword. Pair the free browser run on this page with the priced API when you need the identical permutation inside an automated pipeline without re-implementing grid packing yourself. Invalid inputs return invalid_input and are not charged, which keeps validation cheap while successful transforms remain a fixed item price.

Where columnar transposition fits in lessons, puzzles, and test fixtures

On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a classroom demo to an automated pipeline without changing the rearranged result.