Symmetric Cryptographic Systems
Hewlett-Packard Company Virtual Private Networking Concepts Guide
2-3
Symmetric Cryptographic Systems
Symmetric Cryptographic Systems
Symmetric Cryptographic Systems
Symmetric Cryptographic Systems
A very simple encryption algorithm involves shifting the letters
of the alphabet to the right by some offset. For example if you
had the clear text "AT" and decided to encrypt this data by
shifting each letter 3 letters to the right, you would end up with
DW. In this example, the clear text is AT, the key is 3, the
algorithm is "shift K letters to the right," and the cipher text is
DW. Your encryption formula would look like this:
DW = shift-right ( AT , 3 )
Of course, decryption in this case involves shifting the letters of
the cipher text to the left by the same offset used when the data
was encrypted. Therefore, your decryption formula would look
like this:
AT = shift-left ( DW , 3 )
Note that the key used to encrypt the data is the same key used
to decrypt the data.
Ke = Kd
This algorithm is therefore referred to as symmetric. In this case,
the person encrypting the data and the person decrypting the
data must both know the same key. The strength of the system
relies on the key being kept secret. Symmetric cryptography is
therefore often referred to as secret key cryptography.
A real world metaphor for symmetric cryptography is a lock box
with a single lock. To safely transfer an object from one person
to another, the first person opens the box with a key, puts the
object in the box, and then locks the box. The second person
needs only a copy of the key, and can then open the box and
retrieve the object.
Related
Related
Related
Related
Information
Information
Information
Information
Data Encryption Standard (DES) (page 2-4)
Triple Pass DES (page 2-5)
3DES (page 2-7)
