2 cissp ® Official Study Guide Eighth Edition

Name
Block size
Key size
Advanced Encryption Standard (AES)
128
128, 192, 256
Rijndael
Variable
128, 192, 256
Blowfish (often used in SSH)
64
32–448
Data Encryption Standard (DES)
64
56
IDEA (used in PGP)
64
128
Rivest Cipher 2 (RC2)
64
128
Rivest Cipher 5 (RC5)
32, 64, 128
0–2,040
Skipjack
64
80
Triple DES (3DES)
64
112 or 168
Twofish
128
1–256

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Chapter 6 
■
Cryptography and Symmetric Key Algorithms
Symmetric Key Management 
Because cryptographic keys contain information essential to the security of the cryptosystem, 
it is incumbent upon cryptosystem users and administrators to take extraordinary measures 
to protect the security of the keying material. These security measures are collectively known 
as
key management practices
. They include safeguards surrounding the creation, distribution, 
storage, destruction, recovery, and escrow of secret keys. 
Creation and Distribution of Symmetric Keys 
As previously mentioned, one of the major problems underlying symmetric encryption al-
gorithms is the secure distribution of the secret keys required to operate the algorithms. The 
three main methods used to exchange secret keys securely are offl ine distribution, public key 
encryption, and the Diffi e–Hellman key exchange algorithm. 
 Offline Distribution
The most technically simple method involves the physical exchange 
of key material. One party provides the other party with a sheet of paper or piece of 
storage media containing the secret key. In many hardware encryption devices, this key 
material comes in the form of an electronic device that resembles an actual key that is 
inserted into the encryption device. However, every offl ine key distribution method has 
its own inherent fl aws. If keying material is sent through the mail, it might be intercepted. 
Telephones can be wiretapped. Papers containing keys might be inadvertently thrown in 
the trash or lost.