Double columnar transposition

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

What double columnar transposition is and what this tool returns

The JSON response includes result for the final rearranged string, encoding fixed to columnar_double, mode set to encrypt or decrypt, key1 and key2 echoing the keywords you supplied, key1_length and key2_length, column_order1 and column_order2 as the zero-based original indices in read order for each pass, intermediate showing the string after the first encrypt pass or after the first decrypt undo, input_length and output_length which always match because each transform only permutes, and a formula string that restates the double-pass 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 two non-empty keys, or the request fails with invalid_input naming the missing field. If you need a single keyword only, polyalphabetic shifts, or modern encryption, use those dedicated endpoints; this landing answers only the classical double columnar two-key contract that crypto history chapters and advanced CTF warm-ups already describe.

How text, two keys, and mode are read and how results stay reproducible

The entire non-empty string of each key defines that pass columns, including digits and symbols if you include them, because ordering uses Unicode character comparison rather than stripping to A–Z only. The intermediate field lets teachers and graders show the first-pass grid without re-implementing columnar packing. The preferred payload fields are text for the message, key1 for the first keyword, key2 for the second 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. Key1 accepts key_1, first_key, keyword1, and k1; key2 accepts key_2, second_key, keyword2, and k2. A missing or empty key1 or key2 is rejected with invalid_input and a clear message that names the field so operators can fix the right password without guessing. 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 orders are computed once from each key, then the same heights formula is used on encrypt and decrypt so a full round trip always restores the original payload for any non-empty string under that key pair. Pair the free browser run on this page with the priced API when you need the identical double permutation inside an automated pipeline. Invalid inputs return invalid_input and are not charged, which keeps validation cheap while successful transforms remain a fixed item price.

Where double 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.