Internationalized Domain Names (IDN): Best Practices and Pitfalls

Internationalized Domain Names enable users to register domain names using non-ASCII scripts, making the web more accessible worldwide. While IDNs expand inclusivity, they also introduce technical and security challenges, such as confusable characters, normalization discrepancies, and punycode handling. This article offers best practices for domain registrars, web platforms, and product teams to navigate IDN complexities.

How IDNs work in brief

IDNs are encoded into ASCII-compatible form (ACE) using punycode, allowing domain name systems designed for ASCII to remain compatible. For example, a domain containing Cyrillic characters is converted to an ACE representation starting with the prefix 'xn--'. Browsers decode ACE back into Unicode for display, but underlying systems operate on the ACE strings.

Common pitfalls

• Mixed-script registrations: Registrations that mix scripts can be visually confusing and are often banned or restricted by registries.
• Punycode confusion: Some users do not inspect punycode or certificate details, leaving them vulnerable to spoofed domains.
• Normalization mismatch: Different systems may normalize the Unicode label differently before punycode encoding, potentially leading to inconsistent resolution.

Registrar best practices

• Script rules and restrictions: Implement policies to prevent registrations that are dangerously confusable with established domains, especially high-value brands.
• Pre-registration checks: Use confusable mapping tools to detect visually similar existing registrations.
• Transparent disclaimers: Inform registrants if their chosen label contains mixed scripts or confusable characters.

Platform verification strategies

Platforms that accept user-provided domains or display names should:

• Validate and normalize domain labels consistently across systems.
• Resolve and display both ACE and Unicode forms in administrative UIs so operators can detect suspicious entries.
• Apply stricter verification for transfers and high-privilege operations when the domain label contains confusables.

Browser and user education

Browser vendors have implemented mitigations such as showing punycode for suspicious domains or restricting the use of mixed scripts in visible labels. Encourage users to verify certificate details for sensitive operations and avoid clicking links from untrusted sources.

Incident handling

If you detect a spoofed domain impersonating your brand:

1. Collect technical details including ACE label, WHOIS, and hosting provider info.
2. Coordinate with registrars for takedown or dispute resolution under applicable policies.
3. Update customers and stakeholders with guidance on recognizing genuine domains and reporting suspicious links.

Conclusion

IDNs make the web more inclusive by allowing domains in native scripts, but they require vigilant policies and tooling to prevent abuse. Registrars and platforms should adopt confusable detection, consistent normalization, and user education to mitigate risks. Balanced policies preserve the benefits of IDNs while protecting users and brands.

Note: For high-value domains and trademarked names, maintain monitoring to detect newly registered confusable domains and act quickly when malicious registrations appear.