A Mighty Number Falls.

After eleven months of calculation by computer clusters from three institutions, the prime factors have been found for a 307 digit long number. What does a number with 307 digits look like? Here’s one:

12948719847198741987491874127247975847647607608236582736510756102876082375608237608237562087035612948719847198741987

49187412724797584764760760823658273651075610287608237560823760823756208703561294871984719874198749187412724797584764

760760823658273651075610287608237560823760823756208703561983748103948573933

“This is the largest ‘special’ hard-to-factor number factored to date,” explains EPFL cryptology professor Arjen Lenstra. (The number is ‘special’ because it has a special mathematical form — it is close to a power of two.) The news of this feat will grab the attention of information security experts and may eventually lead to changes in encryption techniques.

Encryption tehniques for securing data rely on the difficulty of factorising huge numbers into their prime factors.

RSA encryption, named for the three individuals who devised the technique (Ronald Rivest, Adi Shamir and Leonard Adleman), takes advantage of this. Using the RSA method, information is encrypted using a large composite number, usually 1024 bits in size, created by multiplying together two 150-or-so digit prime numbers.

Does this mean the security of RSA is under threat?

For the moment the standard is still secure… But the clock is definitely ticking. [EPFL cryptology professor Arjen Lenstra]