[131915] in cryptography@c2.net mail archive
Re: Decimal encryption
daemon@ATHENA.MIT.EDU (=?ISO-8859-1?Q?Thomas_Baign=E8res?)
Thu Aug 28 20:11:05 2008
From: =?ISO-8859-1?Q?Thomas_Baign=E8res?= <thomas.baigneres@epfl.ch>
To: =?ISO-8859-1?Q?Philipp_G=FChring?= <pg@futureware.at>,
cryptography@metzdowd.com
In-Reply-To: <48B56D48.3090109@futureware.at>
Date: Thu, 28 Aug 2008 20:17:14 +0200
Hello,
Actually, block ciphers encrypting blocks of *decimal* numbers exist:
- TOY100 [1] encrypts blocks of 32 decimal digits
- DEAN18 [2] encrypts blocks of 18 decimal digits
- DEAN27 [3] encrypts blocks of 27 decimal digits
TOY100 is (almost) broken by the generalized linear cryptanalysis =20
described in [2]. Both versions of DEAN are based on a substitution =20
permutation network very close to that of the AES and are provably =20
secure against linear cryptanalysis. These ciphers are only "toy" =20
ciphers. Consequently, there is no official implementation (no test-=20
vector, etc.).
Here are the references:
[1] Granboulan, Levieil, Piret: Pseudorandom Permutation Families over =20=
Abelian Groups. FSE 2006: 57-77
[2] Baign=E8res, Stern, Vaudenay: Linear Cryptanalysis of Non Binary =20
Ciphers. Selected Areas in Cryptography 2007: 184-211 (available here: =
http://lasecwww.epfl.ch/~tbaigner/papers/groupLC.pdf=20
)
[3] Baign=E8res (PhD Thesis): Quantitative Security of Block Ciphers: =20=
Designs and Security Tools (to be published)
I hope this helps. I'm of course available for any question regarding =20=
DEANxx.
Best regards,
Thomas Baign=E8res
--
http://lasecwww.epfl.ch/~tbaigner
On Aug 27, 2008, at 5:05 PM, Philipp G=FChring wrote:
> Hi,
>
> I am searching for symmetric encryption algorithms for decimal =20
> strings.
>
> Let's say we have various 40-digit decimal numbers:
> 2349823966232362361233845734628834823823
> 3250920019325023523623692235235728239462
> 0198230198519248209721383748374928601923
>
> As far as I calculated, a decimal has the equivalent of about 3,3219
> bits, so with 40 digits, we have about 132,877 bits.
>
> Now I would like to encrypt those numbers in a way that the result =20
> is a
> decimal number again (that's one of the basic rules of symmetric
> encryption algorithms as far as I remember).
>
> Since the 132,877 bits is similar to 128 bit encryption (like eg. =20
> AES),
> I would like to use an algorithm with a somewhat comparable strength =20=
> to AES.
> But the problem is that I have 132,877 bits, not 128 bits. And I can't
> cut it off or enhance it, since the result has to be a 40 digit =20
> decimal
> number again.
>
> Does anyone know a an algorithm that has reasonable strength and is =20=
> able
> to operate on non-binary data? Preferrably on any chosen number-base?
>
> Best regards,
> Philipp G=FChring
>
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