Problem - Kevin Tafuro

Discussion
Be sure to read this discussion carefully, as well as other related discussions.
While a strong encryption algorithm is a great foundation, there
are many ways to use strong encryption primitives in an insecure way.
There are two general types of ciphers:
Block ciphers
These work by encrypting a fixed-size chunk of data (a block). Data that isn’t
aligned to the size of the block needs to be padded somehow. The same input
always produces the same output.
Stream ciphers
These work by generating a stream of pseudo-random data, then using XOR * to
combine the stream with the plaintext.
There are many different ways of using block ciphers; these are called block cipher
modes. Selecting a mode and using it properly is important to security. Many block
cipher modes are designed to produce a result that acts just like a stream cipher.
Each block cipher mode has its advantages and drawbacks. See Recipe 5.4 for information
on selecting a mode.
Stream ciphers generally are used as designed. You don’t hear people talking about
stream cipher modes. This class of ciphers can be made to act as block ciphers, but
that generally destroys their best property (their speed), so they are typically not used
that way.
We recommend the use of only those ciphers that have been studied by the cryptographic
community and are held in wide regard.
There are a large number of symmetric encryption algorithms. However, unless you
need a particular algorithm for the sake of interoperability or standards, we recommend
using one of a very small number of well-regarded algorithms. AES, the
Advanced Encryption Standard, is a great general-purpose block cipher. It is among
the fastest block ciphers, is extremely well studied, and is believed to provide a high
level of security. It can also use key lengths up to 256 bits.
AES has recently replaced Triple-DES (3DES), a variant of the original Data Encryption
Standard (DES), as the block cipher of choice, partially because of its status as a
U.S. government standard, and partially because of its widespread endorsement by
leading cryptographers. However, Triple-DES is still considered a very secure alternative
to AES. In fact, in some ways it is a more conservative solution, because it has
been studied for many more years than has AES, and because AES is based on a rela-
* Or some other in-group operation, such as modular addition.
Figuring Out Which Encryption Algorithm Is Best | 157
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