Re: interop: PaddingMode.None TripleDES with CrptoAPI

#1

You might try calling CryptEncrypt/CryptDecrypt without the 'final' flag.
That way, the function won't know that it's the final block and thus won't
add/remove any padding.

This approach will probably work with most or all CSPs that are out there.

Regards,
John Banes
[Microsoft Security Developer]

This posting is provided "AS IS" with no warranties, and confers no rights.
Please do not send email directly to this alias. This alias is for newsgroup
purposes only.

"casey chesnut" <casey (AT) braSPAMins-N-braSPAMwn (DOT) com> wrote

Quote:

i'm trying to do TripleDES with no padding in the CryptoAPI

going off this article here:
http://www.di-mgt.com.au/cryptopad.html#example3des

which lists these expected results:
Example using Triple DES with key
0x0123456789ABCDEFFEDCBA987654321089ABCDEF01234567
3DES INPUT BLOCKS: 12345376 06666665 55551205
3DES OUTPUT: 7ADE45981580DB32 421E3D90B5B47D5B 1175FA3DD8B932D7
using an 8 byte IV of all zero.

if i take the 1st block and encrypt it with the CryptoAPI.
then i get 7ADE45981580DB32 (as expected) plus 8 more bytes of padding.
ok, so if i want to encrypt with no padding,
i just do that for 8 block chunks and strip off the trailing 8 each time.
so that should be compatible with the desktop.

but the problem is when i try to decrypt with the CryptoAPI.
if i take the result 7ADE45981580DB32 and append 8 bytes of padding:
0808080808080808,
when i try to decrypt, i get BAD DATA.

what else do i need to do?

Thank you,
casey

#2

i'll have to give that i shot,
below is what i have working right now ...

for CryptEncrypt, i just threw away the last 8 bytes of padding.
for CryptDecrypt, i set the last 8 cipher bytes to the IV,
then Encrypt 0x0808080808080808.
that returned 16 bytes, with the 1st 8 bytes being the pad that i needed.

Thanks,
casey
http://www.brains-N-brawn.com

"John Banes [MS]" <jbanes (AT) online (DOT) microsoft.com> wrote

Quote:

You might try calling CryptEncrypt/CryptDecrypt without the 'final' flag.
That way, the function won't know that it's the final block and thus won't
add/remove any padding.

This approach will probably work with most or all CSPs that are out there.

Regards,
John Banes
[Microsoft Security Developer]

This posting is provided "AS IS" with no warranties, and confers no
rights.
Please do not send email directly to this alias. This alias is for
newsgroup
purposes only.

"casey chesnut" <casey (AT) braSPAMins-N-braSPAMwn (DOT) com> wrote in message
news:OjHGGfIVEHA.2360 (AT) TK2MSFTNGP10 (DOT) phx.gbl...
i'm trying to do TripleDES with no padding in the CryptoAPI

going off this article here:
http://www.di-mgt.com.au/cryptopad.html#example3des

which lists these expected results:
Example using Triple DES with key
0x0123456789ABCDEFFEDCBA987654321089ABCDEF01234567
3DES INPUT BLOCKS: 12345376 06666665 55551205
3DES OUTPUT: 7ADE45981580DB32 421E3D90B5B47D5B 1175FA3DD8B932D7
using an 8 byte IV of all zero.

if i take the 1st block and encrypt it with the CryptoAPI.
then i get 7ADE45981580DB32 (as expected) plus 8 more bytes of padding.
ok, so if i want to encrypt with no padding,
i just do that for 8 block chunks and strip off the trailing 8 each
time.
so that should be compatible with the desktop.

but the problem is when i try to decrypt with the CryptoAPI.
if i take the result 7ADE45981580DB32 and append 8 bytes of padding:
0808080808080808,
when i try to decrypt, i get BAD DATA.

what else do i need to do?

Thank you,
casey

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Re: interop: PaddingMode.None TripleDES with CrptoAPI

Dotnet Security microsoft.public.dotnet.security

Re: interop: PaddingMode.None TripleDES with CrptoAPI - 06-18-2004 , 08:12 PM

Re: interop: PaddingMode.None TripleDES with CrptoAPI - 06-18-2004 , 10:28 PM