Updated: 07:59, Monday November 25, 2013
Twitter has used an 'impossible' mathematical problem first discovered by a British secret agency to protect its users from electronic snooping.
The company said 'perfect forward secrecy' (PFS) was now live on all its services, drastically increasing the effort required to intercept its traffic.
It is understood the move is intended to make it more difficult for data to be collected on its users without going through legal channels.
Jim Killock, director of the Open Rights Group (ORG), said it was a 'policy move' driven by revelations about mass surveillance by British eavesdropping agency GCHQ and the American National Security Agency (NSA).
He said: 'Companies have now realised precisely how vulnerable their information is on the internet. It's no longer a theoretical risk. We know it's been going on now.
In June it was revealed that GCHQ was using a project called Tempora to indiscriminately scoop data from fibre optic cables entering and leaving the UK.
In standard encryption each side of a communication independently generates paired keys - a public key telling others how to encrypt the messages they send to it and a private one used to decode them when they arrive.
The maths involved make it almost impossible to calculate the private key from the public one.
But if an attacker acquires a company's private key it can read anything sent to and from that company's servers - even if it was recorded years earlier.
PFS adds another stage where two machines collaborate on enormous sums to deduce a shared key which is never shared and never used again.
That means an attacker would have to use a more complicated and resource-intensive 'man-in-the-middle' strategy specifically targeted at a single communication while it was still going on.
The so-called 'Diffie-Hellman' method used by Twitter was first discovered by GCHQ analysts in the early 1970s, but remained secret until it was independently patented by a pair of American cryptographers.