On Wed, 27 Aug 2008, Eric Rescorla wrote:

At Wed, 27 Aug 2008 17:05:44 +0200, Philipp Gühring wrote:Hi, I am searching for symmetric encryption algorithms for decimal 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 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. AES), I would like to use an algorithm with a somewhat comparable strength 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 decimal number again. Does anyone know a an algorithm that has reasonable strength and is able to operate on non-binary data? Preferrably on any chosen number-base?There are a set of techniques that allow you to encrypt elements of arbitrary sets back onto that set. The original paper on this is: John Black and Phillip Rogaway. Ciphers with arbitrary ?nite domains. In CT-RSA, pages 114?130, 2002.

But he probably wants an encryption scheme, not a cipher.

`Also, correct me if I am wrong, but Black and Rogaway's approach is not`

`efficient for large domains. But if you use their approach for small`

`domains then you open yourself up to dictionary attacks.`

For a modern proposal to make this a NIST mode, see: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/ffsem/ffsem-spec.pdf -Ekr Full Disclosure: Terence Spies, the author of the FFSEM proposal, works for Voltage, Voltage has a product based on this technology. and I'm on Voltage's TAB and have done some work for them. --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]