IDNs

IDNs, or Internationalized Domain Names, are domain names that include characters beyond the ASCII letter set. They enable use of scripts such as Arabic, Cyrillic, Chinese, Devanagari, and Latin-based characters with diacritics, allowing people to register and access websites in their native writing systems. The Domain Name System (DNS) was designed for ASCII, so IDNs define a way to map Unicode labels to ASCII for DNS lookup while keeping the user-visible form in the original script.

Encoding and resolution often rely on Punycode, an ASCII-compatible encoding. When a Unicode label is prepared for the DNS, it is converted into an ASCII string beginning with the prefix xn--, which can then be stored and resolved by existing DNS infrastructure. The reverse step displays the user’s native script in a browser or application. The Punycode algorithm is specified in RFC 3492, and IDN handling is defined in the IETF IDNA standards, including IDNA2003 and IDNA2008.

Preparation and normalization are part of IDN handling. The process includes mapping certain characters, applying Unicode normalization, and enforcing rules to ensure labels are compatible with DNS syntax and rendering. This helps prevent problems such as ambiguous characters or disallowed combinations.

Security and usability considerations are notable. IDNs introduce the risk of homograph or spoofing attacks, where visually similar characters from different scripts are used to imitate trusted domains. Browsers and registries employ display restrictions, warnings, or policy controls to mitigate these risks, and some UI layers show punycode or mixed-script representations to help users distinguish domains.

IDN support is widespread across major browsers and domain registries, though implementation details and policy choices may vary. The goal is to extend the Internet’s reach while preserving reliable resolution and user safety.