Re: Question about bit strength

On Wed, 13 Sep 2006 10:40:53 +1000, "Antony Clements"
<antony.clements@xxxxxxxxxxxxxxx> wrote:

Hi i'm a software delveoper, for the last few years i have been toying
around with a hybrid block cypher. I have two implementations of the
algorithms i have produced, both work flawlessly to encrypt/decrypt content,
but I am still unsure as to the bit strength of these algorithms. I have had
answers ranging from 64-bit through to 512-bit and beyond depending on who i
have asked to bit test them. All Keys used have elements derived by a
P.R.N.G. and the plain text is padded so that the cypher text is easier to
produce, after which the padding is removed and the cypher text written to a
file so there is no increase in size as with other methods. Each algorithm
is capable of encrypting/decrypting strings well in excess of
18446744073709551615 characters with the ability to encrypt a folder
containing 13 files totalling 227KB in 15-20 seconds. I was wondering if
anyone with the knowledge to bit test my algorithms could please do so.

The strength of a properly implemented secure algorithm is based entirely on
the size of the keyspace and has nothing at all to do with how much data it can
handle or how fast it can handle it. It's equivalent to asking "I built a red
car, can anyone tell me how fast it will go?"

Without professional cryptanalysis of your algorithms you can't be sure your
hybrids have any security at all, no matter how large the keyspace is; even then
that's not a guarantee but it's a lot better than no analysis at all.