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3. Use of Encryption.
Both types of encryption algorithms are widely used in all sorts of applications.
Symmetric encryption algorithms require that sender and recipient(s) share
some secret information beforehand. This information can be used as the source
for the encryption/decryption key.
Asymmetric encryption is used when there is no shared secret between sender
and recipient.
Symmetric encryption algorithms are usually much much faster than asymmetric
algorithms so it is not practical to use asymmetric encryption algorithms
when symmetric can be securely used.
To help out with slowness of asymmetric encryption cryptographers designed
special secure protocols. Idea is to establish common secret key for the current
communication session (called session key) first (using asymmetric encryption)
and then use that session key to encrypt all data exchanged during communication.
Next communication session would repeat it all over again to establish new
session key. So every session would have diff rent session key.
Process of establishing common secret key among different parties is called
Key Exchange protocol. Normally session key is used for one session only and
destroyed immediately after the end of the session.
4. Length of Keys
Length of decryption keys is important for algorithms, which does not have
known mathematical weaknesses (these algorithms usually called cryptographically
strong).
- Symmetric algorithms:
Each additional bit in length of a decryption key doubles the efforts necessary
to guess the right key. 56 bit long key is 65536 stronger that 40 bit long
key.
- Asymmetric algorithms:
There is no generic rule how each additional bit in length of public key
increases the efforts necessary to guess the right private key. It depends
on the nature of each particular algorithm, for more detail check “Applied
Cryptography” by Bruce Schneier (ISBN: 0471117099).
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Energy Secretary fires nuclear security chief apparently for bad information security.
More here.
13 January 2006
No big virus out breaks for long time.
3 January 2006
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