On 21 August 2012 14:14, Charles Mills <charl...@mcn.org> wrote: > Actually, there IS *almost* a general solution to this problem. > > The input consists of characters from some set of 'n' characters. (Perhaps > 'n' is 94 -- 0x21 through 0x7e inclusive -- but it does not matter.) You > need to pack those characters with maximum density. It's conceptually the > easiest if 'n' is 64, but basically you convert each character to an > integer from 0 to 'n', and multiply the first character's value times the > second's times the third's, etc., until you have done all 24.
Actually, I think you mean multiply the first character's value by n, and add the second. Multiply the result by n and add the third etc. Just before you sent this, I was just thinking of exactly the same algorithm!! > You have a problem dealing with the leftover bits when you overflow > whatever size integer your system supports, but it is a solvable problem. > (Perhaps OpenSSL BN will help with this; I don't know.) Yes - it could > Now you end up with a string of somewhat less than 24 bytes: 18 if 'n' is > 6, 20 if n is 94. (Actually 19.2 bytes, which is going to be the problem.) > > Encrypt the 20 bytes (into 20 bytes). Now reverse the process: divide the > result by 'n' and represent the remainder as one of your 'n' legal > characters; repeat until you have converted the whole string. > Unfortunately, because of that leftover .8 byte you are going to end up > with 25 characters. *Almost* a solution. > > If you can figure out a way to encrypt 19.2 bytes into 19.2 bytes rather > than 20 you have it solved. > Your target character space does not have to be the same size as your input character space. If the target character space is bigger by a sufficient amount then this is not a problem. > > Charles > > -----Original Message----- > From: owner-openssl-us...@openssl.org [mailto: > owner-openssl-us...@openssl.org] On Behalf Of Ken Goldman > Sent: Tuesday, August 21, 2012 8:46 AM > To: openssl-users@openssl.org > Subject: Re: OpenSSL DES generates '\n' in encrypted code > > On 8/21/2012 7:17 AM, Matt Caswell wrote: > > > > On 21 August 2012 12:00, Tarun Thakur wrote: > > > >> Output of my software application (after encryption and encoding with > >> any mechanism) should be of 24 bytes containing alphanumeric > >> characters only. > >> > >> So, if I get encrypted 24 bytes from plain 24bytes, then > >> > >> which encoding mechanism can convert encrypted 24bytes into > >> alphanumeric encoded 24bytes? > > > > That is impossible. No encoding mechanism can do that. > > To do the impossible :-), research FPE - format preserving encryption. > > ______________________________________________________________________ > OpenSSL Project http://www.openssl.org > User Support Mailing List openssl-users@openssl.org > Automated List Manager majord...@openssl.org >
