Substitution & shift cipher workbook

Solving a substitution or shift cipher means repeatedly moving between the message, letter frequencies, common words, mapping guesses, and the partial plaintext. Scattered references and separate scratch notes interrupt that process.

I built a single-page workbook to colocate relevant reference information and hands-on analysis. Paste ciphertext, compare its patterns with English frequency data, test cipher-to-plaintext mappings, and inspect the result without leaving the workspace.

The browser recalculates letter counts, within-word pairs, short words, and letter positions. A persistent mapping panel connects each hypothesis to the partial plaintext. Caesar mode exposes all 26 shifts and can infer a shift from a single trial mapping.

Frequency ranks are comparison aids, not an automatic substitution key. Fully filled words remain explicitly unverified. Duplicate plaintext assignments raise a warning so conflicting guesses stay visible.

Mappings are saved locally for each message when browser storage is available. A JSON export retains the analyzed ciphertext and current guesses. The workbook opens with a default ciphertext, analyzed immediately; visitors can replace it with their own text.

The utility uses HTML, CSS, and JavaScript with bundled English reference counts. Analysis runs locally in the browser, without an account, API key, model request, or server-side analysis service.

English rates derive from Peter Norvig’s corpus analysis and its linked word-count data. Counts, percentages, and expected values use explicitly described denominators; corpus artifacts and sample size can affect comparisons.

This is a workbook for basic monoalphabetic substitution and Caesar shifts over A–Z. It does not automatically solve a message, verify a guessed plaintext, analyze modern encryption, or establish correctness from frequency similarity alone.

Browser storage is local convenience, not a backup or an access-control mechanism. Export notes you want to keep, and avoid entering sensitive material on a shared browser.