Opera

Public Key Cryptography is a method where you use two keys, one private, known only to you, and one public, that you may send to every one you are going to communicate with, or post in a database.

Some of the methods work this way:

Anything encrypted with the private key can be decrypted with the public key, and vice versa, but nothing encrypted with the public key, can be decrypted with the public key.

This means that a message encrypted with your private key can be read by anyone, but they will know that it was you who encrypted it. On the other hand, anyone may encrypt a message with your public key, and know that only you can read, by using your private key to decrypt the message.

How secure are these methods? Generally speaking, the methods in use today has not been broken except by brute force, and the amount of brute force needed depends on how large the numbers used in the keys are (Size of keys is given in number of bits).

The method used by Opera, RSA, is based on large prime number (numbers that can only divided by 1 and itself, such as 2, 3, 5, 7, 11 and 13), and the only way known to break a private key is to factor large numbers, which is a very expensive operation in work (number of caclulations), or hardware.

The largest such key that has been broken was a 428 bit key (129 digits), in 8 months. Todays methods usually uses at least 512 bit (154 digits), but more often 1024 (308 digits), and are therefore much more difficult to break; but present methods and technology is believed to be able to break the 512 bit key within a year or so, but the work doubles for every few digits.

The present rule of thumb is, more bits, more security. This means that, use 1024 bit, or more if you can; Opera presently supports keys up to 2048 bit keys, but some servers may not be able to use keys larger than 1024 bit.

These methods are generally very time-consuming, and are therefore only used to send small amounts of data usually less bits than in the key.