TheAlgorithms/Go · error

len(key): %d must be as long as size squared: %d

Error message

len(key): %d must be as long as size squared: %d

What it means

Constructor validation error from NewPolybius: the provided key length does not equal size*size, meaning there are not enough key characters to fill every cell of the square Polybius grid the constructor builds.

Source

Thrown at cipher/polybius/polybius.go:46

	}
	key = strings.ToUpper(key)
	if size > len(chars) {
		return nil, fmt.Errorf("provided size %d is too small to use to slice string %q of len %d", size, chars, len(chars))
	}
	for _, r := range chars {
		if (r < 'a' || r > 'z') && (r < 'A' || r > 'Z') {
			return nil, fmt.Errorf("provided string %q should only contain latin characters", chars)
		}
	}
	chars = strings.ToUpper(chars)[:size]
	for i, r := range chars {
		if strings.ContainsRune(chars[i+1:], r) {
			return nil, fmt.Errorf("%q contains same character %q", chars[i+1:], r)
		}
	}

	if len(key) != size*size {
		return nil, fmt.Errorf("len(key): %d must be as long as size squared: %d", len(key), size*size)
	}
	return &Polybius{size, chars, key}, nil
}

// Encrypt encrypts with polybius encryption
func (p *Polybius) Encrypt(text string) (string, error) {
	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

View on GitHub (pinned to 5ba447ec5f)

Solutions

1. Pad or trim the key to exactly size*size characters before construction
2. Validate key length at the API boundary and surface the required length
3. Generate a key of the correct length from a passphrase

When it happens

Trigger: Thrown at cipher/polybius/polybius.go:46 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/d8aab38c2a1968f6. Report an issue: GitHub.