Homoglyph
In typography, a homoglyph is one of a pair of characters with shapes that are either identical, or cannot be differentiated by quick visual inspection. This designation is also applied to sequences of characters sharing these properties. The term 'homograph' is sometimes used synonymously, but it must be noted that the typographic sense of this term is not inlcuded in the definition normally applied in linguistic discourse. In that context, homography is a property of words, not characters, and homographs are a type of homonym. References to characters in terms of the similarity of their appearance might therefore best be made without reliance on specialized vocabulary, for example, as 'seemingly identical', 'visually similar', 'visually confusable' or 'look-alike' characters.The Unicode Consortium has recently published its Technical Report #36 [1] (http://www.unicode.org/reports/tr36/) on a range of issues deriving from the visual similarity of characters both in single scripts, and similarities between characters in different scripts.
The Unicode character chart contains many strongly homoglyphic characters. These present security risks in a variety of situations (addressed in UTR#36) and have recently been called to particular attention in regard to internationalized domain names. Deliberately substituting one character with another that cannot readily be distinguished from it, allows the spoofing of one domain name by another which apears as though it were a homograph of the first one, but in fact is not. The most notable such exploitation is a phishing attack. In many fonts the Greek letter 'Α', the Cyrillic letter 'А' and the Latin letter 'A' are visually identical, as are the Latin letter 'a' and the Cyrillic letter 'а'. A domain name can be spoofed simply by substituting one of these forms for another in a separately registered name. There are also many examples of near-homoglyphs within the same script such as 'í' (with an acute accent) and 'i'. When discussing this specific security issue, any two sequences of similar characters may be assessed in terms of its potential to be taken as a 'homoglyph pair', or if the sequences clearly appear to be words, as 'pseudo-homographs' (noting again that these terms may themselves cause confusion in other contexts).
Efforts are underway by TLD registries and Web browser designers to minimize the risks of homoglyphic confusion to the fullest extent possible. Relevant documentation will be found both on the developers' Web sites, and on an IDN Forum [2] (http://icann.org/announcements/announcement-20sep05.htm) provided by ICANN.
A familiar manifestation of homoglyphic confusion in a historical regard results from of the use of a 'y' to represent a 'þ' when setting older English texts in fonts that do not contain the latter character. This has led to the mistaken supposition that the word 'The' was formerly written and pronounced as 'Ye', as in 'Ye olde shoppe', instead of the intended 'Þe olde shoppe' (discussed in detail in a separate article on the thorn).
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