Anonymous matching

Anonymous matching is a matchmaking method facilitated by computer databases, in which each user confidentially selects people they are interested in dating and the computer identifies and reports matches to pairs of users who share a mutual attraction. Protocols for anonymous matchmaking date back to the 1980s, and one of the earliest papers on the topic is by Baldwin and Gramlich, published in 1985. From a technical perspective, the problem and solution are trivial and likely predate even this paper. The problem becomes interesting and requires more sophisticated cryptography when the matchmaker (central server) isn't trusted.
The purpose of the protocol is to allow people to initiate romantic relationships while avoiding the risk of embarrassment, awkwardness, and other negative consequences associated with unwanted romantic overtures and rejection. The general concept was patented on September 7, 1999, by David J. Blumberg and DoYouDo chief executive officer Gil S. Sudai, but several websites were already employing the methodology by that date, and thus apparently were allowed to continue using it. United States Patent 5,950,200 points out several potential flaws in traditional courtship and in conventional dating systems in which strangers meet online, promoting anonymous matching of friends and acquaintances as a better alternative:
Implementations.
Some of the most notable implementations of the idea have been:
These commercial implementations all trust the central server, simplifying the solution and implementation drastically. Baldwin and Gramlich solved this case in 1985, as well as the more notable and challenging case in which the central server isn't trusted.
Viral marketing.
eCRUSH, DoYOU2.com, the LiveJournal Secret Crush meme, and SecretAdmirer.com are examples of anonymous matching services using viral marketing to increase their membership. Users are encouraged to send an anonymous email to their crush so that they will visit the site and enter their own crushes, facilitating a match. In the case of SecretAdmirer.com, the email is mandatory; this represents a more aggressive type of viral marketing.
At least one site, CrushLink, was accused by eCRUSH of sending spam emails disguised as crush notifications. According to a Salon article, "What makes SomeoneLikesYou and Crushlink different from the rest of the sites in the genre is this: they bait hopeful visitors to hand over as many e-mail addresses as possible by trading clues for e-mail addresses". Both sites are now defunct.