Re: Java encryption newbie (2)

From:

Patricia Shanahan <pats@acm.org>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 09 Oct 2010 21:35:16 +0100

Message-ID:

<QNSdnQ1IVPtiTC3RnZ2dnUVZ_qCdnZ2d@earthlink.com>

Marco A. Cruz Quevedo wrote:

On Oct 9, 1:15 pm, Roedy Green <see_webs...@mindprod.com.invalid>
wrote:

On Sat, 9 Oct 2010 11:05:39 -0700 (PDT), "Marco A. Cruz Quevedo"
<macr...@myway.com> wrote, quoted or indirectly quoted someone who
said :

The original message is constant and everytime I run the program, the
encrypted message is different. I tried with different length messages
and the encrypted message has same length. What is wrong? Is it
normal?.

It probably is normal. Most encryption algorithms add some "salt", a
random number to the beginning of the message. This way if you keep
sending the same message over and over, a snoop won't be able to tell
that is happening.

Ok, I understand that this makes safer algorithm but, why different
length messages produce encrypted messages with same lenght?

Maybe the algorithm you are using works best on multiples of some chunk
size. If so, the size of the message, after adding any seed, would be
rounded up. Have you tried drastically different message lengths? For
example, comparing one byte to one megabyte.

Patricia