What is encryption?
Encryption is a mathematical process of coding and decoding information. The number of bits (40-bit, 56-bit, 128-bit, 256-bit) tells you the size of the key. Like a longer password, a larger key has more possible combinations. In fact, 128-bit encryption is one trillion times stronger than 40-bit encryption.
When an encrypted session is established, the strength is determined by the capability of the web browser, SSL certificate, web server, and client computer operating system.