Public-key cryptography is a means for authenticating information sent over the Internet. The system works by encrypting and decrypting information through the use of a combination of “keys.” One key is a published “public key; the second is a “private key,” which is kept secret. An algorithm is used to decipher each of the keys. The method is for the sender to encrypt the information using the public key, and the recipient to decrypt the information using the secret private key.

The strength of the system depends on the size of the key: a 128-bit encryption is about 3 × 1,026 times stronger than 40-bit encryption. No matter how complex the encryption, as with any code, keeping the secret aspects secret is the important part to safeguarding the information.

Users can easily tell whether they are on a secure or non-secure Internet website by the prefix of the Web page address. Addresses that begin with “http://” are not secure while those that begin with “https://” are secure.