Re: Unique random string

On Tue, 27 Jun 2000, William Ahern wrote: > Any ideas on how I can generate a 'guaranteed' unique ascii string less than > 15 characters. > > It must be guaranteed unique across several independent > servers. > > Currently we are generating random short strings to create unique aliases for > email addresses. The only problem is that to guarantee uniqueness we keep a log > of previous strings and check to make sure we don't create duplicates (we cannot > rotate strings. They must be absolutely unqiue for the next decade or so). > > The optimal solution would be to generate strings that are truly unique and > hopefully random enough, w/o having to go through the process of checking for > duplicates. > > I'd use uniqid(), except that it is 32 characters (too long since users will > have to handle them sometimes) and the algorithm must be available to C, C++, > Perl, whatever. Concatenate the current time in milliseconds, attach the output of lcg_value() (see ext/standard/lcg.c, it is easy to rip out or emulate in Perl) and calculate the MD5 key of the string. An MD5 key is 128 bits long, so it fits nicely into 15 chars. - Sascha