Short answer, a 256 bit encryption is stronger than a 128 bit key encryption key, but how much stronger?
First, it is important to understand what a bit is. A bit is a single value and can be either 0 or 1. In the case of a 128 bit key the cipher would be 128 bits long, which mathematically means that there are 2e128 possible combinations, or about 3.4 x 10e38. This is an awful lot of combinations, which is what makes it nearly impossible to crack the security encryption. However, as computers get faster the numbers of bits required to ensure secure encryptions needs to be raised. Currently, the strongest level of protection you can get is 256-bit, which equates to 2e256 combinations or about 1.5 x10e77 possible combinations. As you can see, even though it is only twice the number of bits, the encryption is exponentially stronger.
If you look at 128 bit encryption, you will see that there are 88 more bits of key length than a 40 bit encryption. Just that change means that there are 288 more combinations. This makes it much harder hackers to try to crack the code. We’re talking something well beyond the range of the trillions. So, as you might guess, 256 bit encryption is even stronger. (There is an intermediary blog, 192, that really isn’t used much amongst SSL certificate providers.) Both of these types of encryption make use of what is known as Advanced Encryption Standard (AES), which makes use of a special algorithm.
For the most part, 128 bit encryption is more than sufficient. It is complex enough to make a brute force attack mostly useless at this time. The processing power needed, among other things, would render most attackers ineffective. However, as technology advances, it is expected that at some point the industry standard will have to shift to 256 bit encryption for secure sockets layer protection. However, many experts predict that 128 bit encryption will be sufficient for another eight to ten years.
