TheAlgorithms/Go · error

failed decipher: %w

Error message

failed decipher: %w

What it means

Polybius.Decrypt wraps a decipher failure for a rune pair (unknown characters or odd-length remainder) with fmt.Errorf %w, returning an empty string and a wrapped error identifying the failing symbol.

Source

Thrown at cipher/polybius/polybius.go:71

	encryptedText := ""
	for _, char := range strings.ToUpper(text) {
		encryptedChar, err := p.encipher(char)
		if err != nil {
			return "", fmt.Errorf("failed encipher: %w", err)
		}
		encryptedText += encryptedChar
	}
	return encryptedText, nil
}

// Decrypt decrypts with polybius encryption
func (p *Polybius) Decrypt(text string) (string, error) {
	chars := []rune(strings.ToUpper(text))
	decryptedText := ""
	for i := 0; i < len(chars); i += 2 {
		decryptedChar, err := p.decipher(chars[i:int(math.Min(float64(i+2), float64(len(chars))))])
		if err != nil {
			return "", fmt.Errorf("failed decipher: %w", err)
		}
		decryptedText += decryptedChar
	}
	return decryptedText, nil
}

func (p *Polybius) encipher(char rune) (string, error) {
	index := strings.IndexRune(p.key, char)
	if index < 0 {
		return "", fmt.Errorf("%q does not exist in keys", char)
	}
	row := index / p.size
	col := index % p.size
	chars := []rune(p.characters)
	return string([]rune{chars[row], chars[col]}), nil
}

func (p *Polybius) decipher(chars []rune) (string, error) {

View on GitHub (pinned to 5ba447ec5f)

Solutions

1. Unwrap the cause with errors.Is/As before deciding recovery
2. Validate ciphertext length is even and characters exist in the square before decrypting
3. Decrypt in pairs to locate the exact bad position

When it happens

Trigger: Thrown at cipher/polybius/polybius.go:71 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of TheAlgorithms/Go@5ba447ec5f (2026-09-02). Data as JSON: /api/errors/9357ee7c3dcdb9c6. Report an issue: GitHub.