To determine the probability of a birthday pairing, you need the probability of each birthday pairing not having the same birthday taken to the exponent of the number of pairings.
The probability of no birthday pairings for 27 people is (364/365)^(27*26/2)=38%, or a 62% chance that there is at least one birthday pairing. The magical number where the you reach 50% (assuming a 365-day year) is only 23 people. Not that it matters much, but I wanted to set the record straight. Brant Thomsen Sr. Software Engineer Wavelink Corporation > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Brian Hurt > Sent: Monday, March 14, 2005 10:28 AM > To: openssl-users@openssl.org > Subject: Re: The breaking of SHA1 > > The phrase comes from the well known trick question. About how many > people (pulled randomly off the street) do you need together so that you > have about a 50% chance that two of them will have the same birthday? If > you assume that birthdays are spread evenly over the year- i.e. > that there > is a 1 in 365 chance that any random pairing of people will have both > people having the same birthday. The answer is that with as few as 27 > people, you have a 50% chance. This is because with 27 people, there are > 27*26/2 = 351 different pairs of people. Loosely, the number of pairings > goes up with the square of the number of people. > ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager [EMAIL PROTECTED]
