Avaya BCM 4.0 Networking Przewodnik Konfiguracji Pobierz pdf (Strona 653)

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Chapter 68 Virtual Private Networks (VPN) 653

BCM 4.0 Networking Configuration Guide

•ESP

Encapsulating Security Payload (ESP) provides data integrity, source authentication and

confidentiality for IP datagrams by encrypting the payload data to be protected. ESP uses the

Data Encryption Standard (DES) and Triple DES and AES algorithms.

•AH

Authentication Header (AH) provides data integrity and source authentication. The AH

method does not encrypt data.

Encryption method

The encryption method can be AES, Triple DES, 56-bit DES. AES is the strongest encryption and

56-bit DES is the weakest encryption.

•AES

Advanced Encryption Standard (AES) is a symmetric key encryption technique. The AES

algorithm uses one of three cipher key strengths: a 128-, 192-, or 256-bit encryption key. BCM

4.0 supports 128 and 256 bit key strengths.

•Triple DES

Triple DES is an encryption block cipher algorithm that uses a 168-bit key. It uses the DES

encryption algorithm three times. The first 56 bits of the key is used to encrypt the data, then

the second 56 bits is used to decrypt the data. Finally, the data is encrypted once again with the

third 56 bits. These three steps triple the complexity of the algorithm.

• 56-bit DES

56-bit DES is an encryption block cipher algorithm that uses a 56-bit key (with 8 bits of parity)

over a 64-bit block. The 56 bits of the key are transformed and combined with a 64-bit

message through a complex process of 16 steps.

Authentication method

The authentication method can be SHA1 or MD5.

• SHA1

Secure Hash Algorithm (SHA1) produces a 160-bit hash. It is regarded by cryptographers as

being more resistant to attacks than MD5. SHA1 does not encrypt data.

•MD5

Message Digest 5 (MD5) Algorithm produces a 128-bit hash. It is used to confirm the

authenticity of a packet. MD5 does not encrypt data. Also, MD5 provides integrity that detects

packet modifications.

Both SHA1 and MD5 use Hashed Message Authentication Code (HMAC) to improve

authentication. HMAC is a technique that uses a secret key and a message digest function to create

a secret message authentication code.

Note: The use of a NAT device in the IPSec tunnel path can sometimes cause the AH

method to report a security violation. This occurs because the NAT device changes the IP

Address of an AH authenticated packet causing the authentication of this packet to fail.

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