## CCNA Security notes.

Over the next few days I am going over my notes for the CCNA Security exam, and I am going to post some of them up here. I am going to start this blog with Symmetric & Asymmetric types.

Starting with symmetric encryption, this comes in the following flavours/sizes:

*DES – 56-bit keys
3DES -112 & 168 –bit keys
AES – 128, 192 & 256 – bit keys
IDEA – 128 – bit keys
RC2 – 40 & 64 –bit keys
RC4 – 1 to 256 – bit keys
RC5 – 0 to 2040- bit keys
RC6 – 128, 192 & 256 – bit keys
Blowfish – 32 to 448 – bit keys*

The symmetric algorithm uses the same key to encrypt and decrypt the data. This means that both the sender and receiver must share the same key to transfer the data securely. The key must always remain a secret; otherwise if someone knows it they can decrypt/encrypt the messages.

The most common techniques used my symmetric encryption cryptography are:

*Block cipher.*

These algorithms work on chunks of specific sized data along with a key resulting in blocks of cipher text.

** Stream cipher**.

A symmetric encryption algorithm that processes the data a bit or a byte at a time with a key resulting in a randomized cipher text or plaintext.

*Message Authentication Code (MAC).*

A message authentication code (MAC) is an authentication tag (also called a checksum) derived by applying an authentication scheme, together with a secret key, to a message.

Typically symmetric encryption is used for VPN’s as they are quicker for bulk encryption for data privacy.

Asymmetric encryption is unlike symmetric encryption as it uses two different keys. One key is used for encryption, the other decryption. The aspect of this is that the decryption key cannot be calculated from the encryption key and vice versa. This makes asymmetric encryption much slow (up to 1000 times in fact). They are mainly used for low volume cryptographic methods.

Asymmetric encryption, this comes in the following flavours:

RSA

Diffie-Hellman

Elliptic Curves

More over the next few days.

BE.