The "solution" to Drake's cryptogram. Image from D. Vakoch, in Mercury, March 1999.
Drake's cryptogram is a coded message devised by Frank Drake and sent to a number of scientists to gauge the difficulty in deciphering artificial extraterrestrial signals. The message, consisting of a string of 1,271 ones and zeros (or bits), was sent to all of the participants following the Green Bank conference in November 1961.
The key was to recognize that 1,271 is the product of two prime numbers, 31 and 41, so that the information is intended to be displayed on a grid of 31 bits by 41. There are two possibilities: 41 lines of 31 bits each, or 31 lines of 41 bits each. The first possibility yields nothing of significance, but the second gives a meaningful picture.
Only one of the recipients, Bernard Oliver was able to decode the message. Given that all involved were of the same species, spoke the same language and were familiar, to some extent, with the workings of Drake's mind, some idea emerges of the problems to be faced in interstellar communication.