Bernstein has discovered cracks in TLS and SSL when they’re combined with another encryption scheme known as RC4. The system invented in 1987 is one of the most popular and most widely recommended mechanisms for protecting traffic on banking, email, and other private sites.
Kenny Paterson, a professor at Royal Holloway, University of London who worked with Bernstein said it was known that RC4 is weak in all kinds of ways. But until now no one has been able to put it all together to break TLS. RC4, invented by legendary cryptographer Ron Rivest for the security firm RSA, uses a key value to generate a stream of seemingly random numbers that can be combined with bits in a message to scramble them in ways that only someone with access to the same key value can unscramble.
Its weakness is that the stream of random numbers isn’t as random as it looks. If you feed the same message through the encryption scheme again and again, the cryptographers could find enough non-random “biases” occur in the scrambled data. While it does take a gigantic number of identical messages the attack in its current form takes close to 32 hours to perform. It is still worthwhile in some cases.