Nameprep is the process of case-folding a

string String or strings may refer to: * String (structure), a long flexible structure made from threads twisted together, which is used to tie, bind, or hang other objects Arts, entertainment, and media Films * ''Strings'' (1991 film), a Canadian ani ...

to lowercase and removal of some generally invisible code points before it is suitable to represent a

domain name A domain name is a string that identifies a realm of administrative autonomy, authority or control within the Internet. Domain names are often used to identify services provided through the Internet, such as websites, email services and more. As ...

, or other such canonical name. It is used by the Internationalizing Domain Names in Applications (IDNA) standard, using the

Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, whic ...

standard for NFKC normalization. Nameprep is defined in RFC 3491, "Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN)", as a profile of stringprep, which is described in RFC 3454, "Preparation of Internationalized Strings ("stringprep")." It does not map lookalike characters to a single character nor prohibit the use of lookalike characters. There are good reasons for this, such as the fact that same sets of characters may be lookalikes in some fonts but not in others, and the fact that any decision on which character to map to will obviously provide a bias towards users of one script; but it also has potentially grave implications for security if not considered by the designers and administrators of systems based on nameprep (the best known example of this being VeriSign's handling of IDNA names in .com and .net).

See also