Encryption Software - Choosing Encryption

Choosing Encryption

There are several factors that affect the choice of an encryption algorithm including speed and security. The simplest method would be an XOR operation, with a constant value, of each byte of plain text, to produce a cipher value .

Ciphers can be categorized into two general types: public key ciphers and symmetric key ciphers.

Public key systems are based upon algorithms that are at least strongly believed to be "one-way" operations. That is, encryption with one member of a key pair is only easily reversed (decrypted) using the other member of the pair. Further, one member of the pair (the public key) cannot be easily used to determine the other (the private key). Provided the problems posed by the system to cryptanalyst are effectively unsolvable, the system is effectively secure. Such systems are used for key exchanges (for subsequent use of symmetric key ciphers), digital signatures and the like.

Symmetric key ciphers (also referred to as secret key ciphers) are called such because the same key is used for both encryption and decryption. Thus, in order for messages encrypted with a symmetric key cipher to remain secure, the key used must remain secret. Symmetric key ciphers can be further subdivided into stream ciphers and block ciphers.

Stream ciphers typically encrypt plaintext a bit or byte at a time, and are most commonly used to encipher real-time communications, such as audio and video information. The key is used to establish the initial state of a key-stream generator, and the output of that generator is used to encrypt the plaintext.

Block cipher algorithms encrypt blocks of bytes of plaintext a block at a time. The Advanced Encryption Standard algorithm (AES - derived from the Rijndael cipher algorithm) is a block cipher that processes 16 bytes at a time, while its predecessor, the Data Encryption Standard algorithm (DES) encrypted blocks of eight bytes.

A common mistake made by amateur cryptographers is the assumption that because the method is secret, the cipher is secure. This is not usually true. Many "home grown" encryption algorithms reveal the key quite easily when fed a string of identical bytes (e.g., nulls).

The purpose of disseminating an encryption method is to allow the community to evaluate it. If it is indeed secure, then its power lies in the fact that its method has been subjected to scrutiny and found to be sound, not that it is secret.