gchq/CyberChef · error · OperationError

Invalid Plaintext character : ${letter}

Error message

Invalid Plaintext character : ${letter}

What it means

Thrown by the Lorenz SZ operation when, in plaintext Send mode (intype !== 'ITA2' and mode !== 'Receive'), an input character is not in the supported plaintext character set. Each character is upper-cased and looked up in validChars; a miss throws at Lorenz.mjs:519. The plaintext path then translates the character into ITA2, inserting figure/letter shifts as needed, so only characters it can encode are permitted.

Source

Thrown at src/core/operations/Lorenz.mjs:519

     */
    convertToITA2(input, intype, mode) {
        let result = "";
        let figShifted = false;

        for (const character of input) {
            const letter = character.toUpperCase();

            // Convert input text to ITA2 (including figure/letter shifts)
            if (intype === "ITA2" || mode === "Receive") {
                if (validITA2.indexOf(letter) === -1) {
                    let errltr = letter;
                    if (errltr==="\n") errltr = "Carriage Return";
                    if (errltr===" ") errltr = "Space";
                    throw new OperationError("Invalid ITA2 character : "+errltr);
                }
                result += letter;
            } else {
                if (validChars.indexOf(letter) === -1) throw new OperationError("Invalid Plaintext character : "+letter);

                if (!figShifted && figShiftedChars.indexOf(letter) !== -1) {
                    // in letters mode and next char needs to be figure shifted
                    figShifted = true;
                    result += "55" + figShiftArr[letter];
                } else if (figShifted) {
                    // in figures mode and next char needs to be letter shifted
                    if (letter==="\n") {
                        result += "34";
                    } else if (letter==="\r") {
                        result += "4";
                    } else if (figShiftedChars.indexOf(letter) === -1) {
                        figShifted = false;
                        result += "88" + letter;
                    } else {
                        result += figShiftArr[letter];
                    }

View on GitHub (pinned to 4290ea7539)

Solutions

1. Restrict input to the supported plaintext character set (basic A-Z, digits, and the punctuation symbols the operation encodes).
2. Pre-sanitise input: strip or transliterate unsupported characters (e.g. smart quotes to ASCII, remove emoji) before running.
3. If your data is already ITA2, switch 'Input Type' to 'ITA2' instead.
4. Check the operation description / wiki for the exact plaintext alphabet supported.

Example fix

// before — unsupported Unicode in plaintext path
input = '“HELLO” — café ☕';

// after — transliterate to supported plaintext
input = '"HELLO" - cafe';

// Approximate allow-list for the Lorenz plaintext path.
const VALID_PLAIN = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 .,?!:;\'"()-/+=&%#\n';
function onlyPlaintext(str) {
  return [...str.toUpperCase()].every(c => VALID_PLAIN.includes(c));
}
if (intype !== 'ITA2' && mode !== 'Receive' && !onlyPlaintext(input)) {
  throw new Error('Input has unsupported plaintext characters');
}

function isLorenzPlaintext(v: unknown): v is string {
  if (typeof v !== 'string') return false;
  const allowed = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 .,?!:;\'"()-/+=&%#\n';
  return [...v.toUpperCase()].every(c => allowed.includes(c));
}

When it happens

Trigger: Running the Lorenz operation with 'Input Type'='Plaintext' and 'Mode'='Send' (the default encoding direction) while the input contains a character the operation cannot represent in ITA2 — e.g. extended Unicode, emojis, accented letters, or punctuation not in the supported set. Raised at Lorenz.mjs:519.

Common situations: Pasting rich text / Unicode (curly quotes, accented characters, emoji) into the plaintext field; expecting arbitrary ASCII punctuation to be encodable; feeding binary/garbage data through the plaintext path.

Related errors

• Invalid ITA2 character : ${errltr}
• Χ1 custom lugs must be 41 long and can only include . or x
• Χ2 custom lugs must be 31 long and can only include . or x
• Χ3 custom lugs must be 29 long and can only include . or x
• Χ4 custom lugs must be 26 long and can only include . or x

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/b7ad8903633a7bdc. Report an issue: GitHub.