On Tue, Oct 29, 2013 at 03:54:50PM +0100, Luis Rocha wrote:
> The X.923 padding attaches to a complete message block another block of
> zeros: A = 00 00 00 00 00 00 00 00
I would expect the last padding byte to be 08, not 00, since 8 padding
bytes were added. PKCS#7 padding for the same complete block would be:
08 08 08 08 08 08 08 08
> $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
Which decrypts to:
$ perl -e '
$x="f90aba97690caf10ea3bc77ae91defe2";
$x =~ s/(..)/chr(hex($1))/eg; print $x;' |
openssl enc -d -nopad -des-ecb -K 0101010101010101 |
od -tx1
0000000 61 61 61 61 61 61 61 61 f1 02 b2 9f 61 04 a7 18
0000020
which is what we expect, since XOR of 08 into each byte of the last block
yields the first block of ciphertext.
> 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
Well it is certainly rather unexpected, to say the least, for the
ciphertext of a full block to contain the plaintext as its second
block. OpenSSL is working correctly. Your CrypTool is not. Help
with using CrypTool is likely a topic for another list.
--
Viktor.
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