On Sat, May 12, 2012 at 12:15 AM, <scott...@csweber.com> wrote: > Ahhh! > So, a 15 byte block (or ends with a 15 byte after multiples of 16 bytes) > would use a 0x01 in the last position...? > > And a whole multiple of 16 blocks would have an extra block filled with > 0x0f's...?
0x10, actually. > > My initial testing now looks like I can get it to work. > > Thanks! > > -Scott Weber > > -------- Original Message -------- > Subject: RE: Looking for (easy) help. > From: "Dave Thompson" <dthomp...@prinpay.com> > Date: Fri, May 11, 2012 3:45 pm > To: <openssl-users@openssl.org> > >>From: owner-openssl-us...@openssl.org On Behalf Of scott...@csweber.com >>Sent: Friday, 11 May, 2012 17:09 > >>I manually padded the input in the C code with spaces. Then I >>manually padded the input file with spaces. Now both cleartexts >>are exactly 16 bytes long. > >>The output from the openssl executable is now 32 bytes...? >>Where did it decide to do that? > >>So, what do I decide how to pad? How far out do I pad it? > > The padding most cryptography uses and openssl commandline > (and EVP_*) does is NOT spaces, it is a count of unused octets > repeated. It was popularized by PKCS#5, see RFC 2898 6.1.1-2. > Because the padding is always nonempty to avoid ambiguity, > if the cleartext is an exact multiple of the blocksize, > padding adds an extra block (and unpadding removes it). > > Marek showed you an example, although it's ambiguous because > by coincidence his last plaintext byte was 0a (newline) > and his padding bytes were also 0a (16-6=10). > > When you call AES_* (or DES_* etc) directly, you must add > the padding on encrypt and remove it on decrypt yourself. > > > ______________________________________________________________________ > OpenSSL Project http://www.openssl.org > User Support Mailing List openssl-users@openssl.org > Automated List Manager majord...@openssl.org > > ______________________________________________________________________ > OpenSSL Project http://www.openssl.org User Support Mailing List > openssl-users@openssl.org Automated List Manager majord...@openssl.org ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager majord...@openssl.org
