The encryption algorithm was changed to AES (Advanced Encryption Standard)
with a 128 bit key length starting with WinRAR 3.0.
The US Government created an encryption standard several
years ago, called the Data Encryption Standard (DES).
It has been widely used both in government circles and by banks.
The government has recently replaced DES with the
Advanced Encryption Standard (AES).
One cryptologist has said that assuming that you could recover a
DES key in a second (trying 2^55 keys per second),
it would take the same machine approximately 149 trillion
years to recover a 128-bit AES key.
Further information:
http://csrc.nist.gov/encryption/aes/WinRAR encryption includes parts of code from Szymon Stefanek
and Brian Gladman AES implementations and Steve Reid SHA-1 source.
The ZIP format uses a proprietary encryption algorithm.
RAR archives are encrypted by the much stronger AES-128
standard. If you need to encrypt important information,
it is better to select the RAR archive format.
19.07.2006, 20:11 
