Front cover - IBM Redbooks

its for RSA and 160 bits for ECC, corresponding to a symmetric block cipher
key size of 80 bits. NIST has published a list of recommended elliptic curves
for protection of 5 different symmetric keysizes (namely, 80, 112, 128, 192,
and 256).
Advantages of asymmetric key algorithms
As we have shown, there are a number of asymmetric key algorithms in use. In
addition to those already mentioned, we cover those used in Notes, Domino, and
other Lotus collaboration products later in this book. For now, let’s talk about the
advantages that all asymmetric key algorithms share in common.
Asymmetric key algorithms offer easier administration of the keys since there is
no need to find a secure channel to get a copy of the key to the intended
recipient. The private key stays private and the public key is public. In other
words, the big advantage of this mechanism over the symmetric key mechanism
is that there is no longer any secret to share. In fact, it does not matter who has
the public key, because it is useless without the matching private key.
Another major advantage of asymmetric key algorithms is that they can provide
digital signatures that cannot be repudiated. We discuss that in a later section.
Disadvantages of asymmetric key algorithms
The disadvantage of asymmetric key algorithms is that they are very slow. In
contrast, there are many secret-key encryption methods that are significantly
faster than any currently available public-key encryption method. This is because
of the fact that you need large key lengths to get comparable security of smaller
symmetric keys.
1.4.4 The hybrid algorithm
An asymmetric key algorithm can be used with a symmetric key algorithm to get
the best of both worlds. For encryption, the best solution is to combine both types
of algorithms in order to get both the security advantages of asymmetric key
algorithms and the speed advantages of symmetric key algorithms.
Thus, this is a hybrid solution which uses a symmetric key for data encryption,
and asymmetric keys for symmetric key encryption. Such a marriage is called a
digital envelope.
In addition, the symmetric key is generally generated every time and is called a
“session” key. It is valid the whole time two people are exchanging messages
with each another. This protocol is used in almost all “public key encryption” such
as Notes, SSL, S/MIME. It provides fast performance and is easy to implement.
Chapter 1. Fundamentals of IT security 33