GNU Libidn is an implementation of the Stringprep, Punycode, and IDNA
specifications defined by the IETF Internationalized Domain Names (IDN)
working group. It is used to prepare internationalized strings (such as
domain name labels, usernames, and passwords) in order to increase the
likelihood that string input and string comparison work in ways that
make sense for typical users around the world. The library contains a
generic Stringprep implementation that does Unicode 3.2 NFKC
normalization, mapping and prohibition of characters, and bidirectional
character handling. Profiles for iSCSI, Kerberos 5, Nameprep, SASL, and
XMPP are included. Punycode and ASCII Compatible Encoding (ACE) via
IDNA is supported.