Earlier I called making predictions foolish. Now I am about to make some. Table 4 gives my recommendations for public-key lengths, depending on how long you require the key to be secure. There are three key lengths for each year, one secure against an individual, one secure against a major corporation, and the third secure against a major government. That is, we would not set free an Internet worm or virus to find resources for us.
Many organizations have several thousand machines each on the net.
Making use of their facilities would require skillful diplomacy, but should not be impossible. Assuming the 5 mips average power, and one year elapsed time, it is not too unreasonable to embark on a project which would require half a million mips years. Also assume that computing power will increase by a factor of ten every five years. And finally, assume that advances in factoring mathematics allows us to factor general numbers at the speeds of the special number field sieve. Table 4 recommends different key lengths for security during different years.