User's Manual

53
8 Appendixes
8.1 Symmetric cryptography
Symmetric algorithms use a single numeric key used both for encrypting and decrypting data. A secure message is
encrypted for the receiver by using a key that is known only to the sender and the receiver. The principle on which the
algorithm is based is that by encrypting a plain text with a certain key and by decrypting the encrypted text with the
same key it is possible to obtain the same plain text again (see figure 8.1).
D
k
(E
k
(P
k
)) = P
Where:
P = plain text
E = encrypting operation
D = decrypting operation
K = key
Encryption Dencryption
Ciphertext
Message
Original
Message
Figure 8.1 – Operating layout of a symmetric algorithm
The most common symmetric algorithms are AES, CAST, DES, 3DES, RC2, RC4, RC5, IDEA, Blowfish.
8.2 AES
The Advanced Encryption Standard (AES),
is a block encryption algorithm used as standard by the USA government
AES is the implementation of a more general algorithm known as Rijndael.
AES can have 128, 192, or 256 bit encryption keys. WebIdentity uses 256 bit encryption.
To date is is considered an extremely secure algorithm and it can be estimated that it will be used successfully all over
the world as it happened to its predecessor, the Data Encryption Standard (DES).
See [AES197] or:
http://en.wikipedia.org/wiki/Advanced_Encryption_Standard
http://it.wikipedia.org/wiki/Advanced_Encryption_Standard