idn

Internationalized Domain Name (IDN) refers to a domain name that contains non-ASCII characters, enabling scripts such as Arabic, Cyrillic, Chinese, Devanagari, and others to be used in Internet addresses. IDN works within the existing Domain Name System by encoding non-ASCII labels into ASCII so that DNS queries can be carried out.

Because the DNS historically required ASCII, IDN uses ASCII Compatible Encoding (ACE) through the Punycode algorithm to represent Unicode strings as ASCII. Each label is converted to an ASCII string, typically starting with the prefix xn--, and the labels are joined with dots for DNS lookup. Applications often convert between Unicode for user display and ASCII for DNS resolution.

Standards and deployment are overseen by the IETF within the IDNA framework, with Punycode defined in RFC 3492. The IDNA specifications have evolved, including newer approaches such as IDNA2008. Modern browsers, registries, and email clients generally support IDN and IDN-based top-level domains in non-Latin scripts, broadening accessibility for multilingual users.

Usage and examples: IDN is widely adopted across languages and scripts, allowing domain names in Arabic, Chinese, Cyrillic, and other character sets. There are IDN top-level domains and registries that host non-Latin script domains, alongside ASCII-based TLDs that support internationalized registrations.

Security and limitations: IDN introduces risks such as spoofing and homograph attacks, where visually similar characters from different scripts can be mistaken for one another. Mitigations include normalization rules, script restrictions, and user education, as well as registrar and software measures to reduce confusion. Ongoing updates to Unicode data and IDNA processing standards remain important for safe use.