In fact, a cryptographic algorithm can become weak or unacceptable at any point in time. What is also true is that all cryptographic methods used in practice at any point in time will become weak at some point in the future due to the advances made in computing over the years.
Since the early days in modern crypto, we knew that we would have to update the methods we use on a regular basis. Unless we use an extremely large size key -- which is not very practical, obviously -- we would need to update symmetric keys from 128- to 256 to higher values, and similarly for asymmetric keys. The experience we had a few years ago with the discovered MD5 weaknesses did not seem to change the way we look at the use of crypto.
Someday we may be able to gracefully increase key sizes without major disruptions, but what happens if an algorithm is known to be weak as was the case with MD5. Can we perhaps use a backup certificate with a different algorithm that is created at the same time and is used when the primary certificate used a weak algorithm?
Recognized in the industry as the "inventor of SSL," Dr. Taher Elgamal led the SSL efforts at Netscape. He also wrote the SSL patent and promoted SSL as the Internet security standard within standard committees and the industry. Dr. Elgamal invented several industry and government standards in data security and digital signatures area, including the DSS government standard for digital signatures. He holds a Ph.D. and M.S. in Computer Science from Stanford University.