Slide 24 of 115
Notes:
Public key cryptography, also known as asymmetric cryptography, solves the key exchange problem by defining an algorithm which uses two keys, each of which may be used to encrypt a message. If one key is used to encrypt a message then the other must be used to decrypt it. This makes it possible to receive secure messages by simply publishing one key (the public key) and keeping the other secret (the private key).
Anyone may encrypt a message using the public key, but only the owner of the private key will be able to read it. In this way, Alice may send private messages to the owner of a key-pair (the bank), by encrypting it using their public key. Only the bank will be able to decrypt it.
In a web server/browser context, terms like “40-bits”, “56-bits”, and “128-bits” refer to the size of the temporary encryption key used for the duration of the SSL session. The size of your permanent private or public key is independent of the size of the temporary SSL session key. Thus, your 56-bit browser is capable of authenticating you to a 56-bit web server by presenting your 1024-bit public key.
