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. 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.) 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. 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
