This is Crypt::CBC, a Perl-only implementation of the cryptographic
cipher block chaining mode (CBC).  In combination with a block cipher
such as Crypt::DES or Crypt::IDEA, you can encrypt and decrypt
messages of arbitrarily long length.  The encrypted messages are
compatible with the encryption format used by B<SSLeay>.

IMPORTANT NOTE: Versions of this module prior to 2.17 were incorrectly
using 8 byte IVs when generating the old-style RandomIV style header
(as opposed to the new-style random salt header). This affects the
Rijndael algorithm, which has a 16 byte blocksize. The bug has been
corrected in versions 2.17 and higher, but in order to read legacy
encrypted data, you will have to pass the B<-legacy_iv> option to
new() using a true value.


Prerequisites
-------------

In addition to this module you will need to install the MD5 module,
and one or more of: Crypt::DES, Crypt::DES_EDE3, Crypt::IDEA, 
Crypt::Blowfish, or Crypt::Rijndael modules.

1. Digest::MD5
   Required for key and iteration vector generation.

2. Crypt::DES
   Required for the DES encryption algorithm.

3. Crypt::DES_EDE3
   Required for the triple DES encryption algorithm in Encrypt Decrypt 
   Encrypt mode. Note, this depends on Crypt::DES.

4. Crypt::IDEA
   Required for the IDEA encryption algorithm.

5. Crypt::Blowfish
   Required for the Blowfish encryption algorithm.

6. Crypt::Blowfish_PP
   Required for the Blowfish_PP encryption algorithm.

7. Crypt::Rijndael
   Required for the Rijndael/AES encryption algorithm.

You can find these modules on a CPAN server near you!

Unfortunately, Crypt::TripleDES does not work with this module, owing
to the fact that it does not follow the same API as the other Crypt::*
modules.  Please write to TripleDES's author, Vipul Ved Prakash
<mail@vipul.net> and ask him to fix this.

Installing Crypt::CBC
---------------------

The rest is easy

	1. perl Makefile.PL
	2. make
	3. make test
	4. make install

Versions 1.22 and greater generate a random initialization vector, 
rather than generating one based on the key.  Not only is this much 
more secure, but it maintains compatibility with the current version of 
OpenSSL, which does the same thing as of version 0.9.5.  For backwards
compatibility, messages encrypted with older versions of Crypt::CBC
can be decrypted with the newer version.  The reverse is not true --
the beginning messages encrypted by the new version and decrypted by
the old may be contaminated with "junk".

Lincoln D. Stein
lstein@cshl.org