Ok so I read more about it and for DES a block consists of 64 bit = 16 hex characters.... The X.923 padding attaches to a complete message block another block of zeros: A = 00 00 00 00 00 00 00 00
so I created a text file with 64 bits (16 hex characters) $echo -n 'aaaaaaaa' > topsecret.txt $xxd topsecret.txt 6161 6161 6161 6161 Then encrypted it with a weak key and iv = 0. openssl enc -des-cbc -K 0101010101010101 -iv 0000000000000000 -nosalt -in topsecret.txt | xxd f90a ba97 690c af10 ea3b c77a e91d efe2 Made the same exercise in the tool: In the tool (GUI) using DES CBC mode with the same key '0101010101010101' the output is: F90A BA97 690C AF10 6161 6161 6161 6161 Much better now...the first block matches....so I think the differences are due to the padding. Does it sound right? On Tue, Oct 29, 2013 at 3:18 PM, Luis Rocha <luiscro...@gmail.com> wrote: > Thank you Victor! > > In the cryptool I'm only able to introduce the 8 bytes key and not the IV. > The documentation from CrypTool says" CBC mode is used with zero > initialization vector and X.923 padding." > > user@debian:~$ openssl enc -des-cbc -K 0101010101010101 -iv > 0000000000000000 -nosalt -in topsecret.txt | xxd > 8a08 216b 7f88 7ec4 > > In the tool (GUI) using DES CBC mode with the same key '0101010101010101' > the output is '255B DF6C 2E64 E96A' but I didnt figure out what they mean > by "zero initialization vector and X.923 padding". > > btw: the tool is quite amazing for learning crypto stuff > > https://www.cryptool.org/images/ct1/presentations/CrypToolPresentation-en.pdf > > Best, > Luis > > > > > On Tue, Oct 29, 2013 at 12:40 AM, Viktor Dukhovni < > openssl-us...@dukhovni.org> wrote: > >> On Mon, Oct 28, 2013 at 11:48:22PM +0100, Luis Rocha wrote: >> >> > + Filename topsecret.txt which only contains the character 'a' >> > + Encrypt it with DES using CBC mode with key and iv = 0 produces the >> > result '32ea a0fa 4f77 fb92' >> > >> > user@debian:~$ openssl enc -des-cbc -K 0 -iv 0 -nosalt -in >> topsecret.txt >> > 0000000: 32ea a0fa 4f77 fb92 2...Ow.. >> >> Note, "0" is not a valid DES key, nor a valid DES iv. To be a >> valid key it needs to be 8 bytes with the right parity bits. So >> >> I don't believe that you can expect well-defined behaviour with >> the specified inputs. >> >> > If I use the cryptool 1.4.31 to do the same exercise the result is >> > '0C29 5D71 8258 D464' >> >> What does "same" mean? What is the syntax for key/iv in that utility? >> >> > I also noticed that openssl generates the same output for different >> modes >> > of des e.g. >> > >> > user@debian:~$ openssl enc -des-ecb -K 0 -iv 0 -nosalt -in >> topsecret.txt | >> > xxd >> >> For a single block with a zero IV, the output of ECB and CBC is >> naturally the same. If you use a non-zero IV, you'll observe that >> CBC and ECB produce different results. >> >> > While if I do the same in Cryptool the output for the ECB mode is: >> > >> > '841B D8A4 2931 FCF5' >> >> Which shows that this tool is not in fact using a zero IV, likely >> because your input is invalid. >> >> -- >> Viktor. >> ______________________________________________________________________ >> OpenSSL Project http://www.openssl.org >> User Support Mailing List openssl-users@openssl.org >> Automated List Manager majord...@openssl.org >> > >
