Encrypting and Decrypting Data

Encryption is the process in which data (plaintext) is translated into something that appears to be random and meaningless (ciphertext). Decryption is the process in which the ciphertext is converted back to plaintext.

A symmetric encryption key (also known here as a session key) is used during both the encryption and decryption processes. In order to decrypt a particular piece of ciphertext, you must possess the key that was used to encrypt the data. Essentially, a session key merely consists of a random number, of approximately 40 to 2000 bits in length. The longer the key that is used, the more difficult it is to decrypt a piece of ciphertext without possessing the key.

The goal of every encryption algorithm is to make it as difficult as possible to decrypt the generated ciphertext without using the key. If a really good encryption algorithm is used, then there is no technique significantly better than methodically trying every possible key. Even for a key size of just 40 bits, this works out to 240 (just over 1 trillion) possible keys.

It is surprisingly difficult to determine just how good an encryption algorithm is. Algorithms that look promising sometimes turn out to be very easy to break, given the proper attack. When selecting an encryption algorithm, it is probably a good idea to choose one that has been around for a while, and successfully resisted all attacks thus far.

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