Re: Get incorrect Result using CBC_MAC

[Haytham Mohammed]

Hi Alexander

 

The problem is in passing the initial vector to the CBC_MAC object

I think the object is using a default IV.

 

I faced the same problem in setting the IV too.

 

and I encrypted the data using DES in CBC mode instead, as u described in the mail.

 

we have the same problem my friend :)

Passing the Initial vector to CBC_MAC<DES> object?

 

Regards

Haytham

Alexander Chaloupka <[EMAIL PROTECTED]> wrote:

Hi
I want to calcualte a MAC with a DES_EDE2 key, but I always get a wrong
result.
If I calculate it by hand or use DES and DES2 encryption the result is
correct.
I'm using Crypto++ 5.2.1 on Windows XP.

Here the example:

BYTE pbSMMACKey[16] = {0xED, 0x43, 0x3E, 0x1A, 0x97, 0x34, 0x99, 0x6C, 0xD9,
0x93, 0xD9, 0xFA, 0xFD, 0xCE, 0x0C, 0xAB};

BYTE pbTestdata[] = {0xC1, 0x6F, 0xE7, 0x89, 0x49, 0xF9, 0xF1, 0xDD, 0x99,
0x02, 0x90, 0x00, 0x80, 0x00, 0x00, 0x00};

BYTE pbIV[8] = {0x00, };
BYTE pbDesOut[256];
BYTE pbMACOutBuffer[8];

CBC_MAC cbcMac(pbSMMACKey);
cbcMac.CalculateDigest(pbMACOutBuffer, pbTestdata, 16);

The (incorrect) result is: 78 69 6b fb fe d3 4b 65


When using DES for the first Block and DES2 with IV for the second Block the
result is OK:

CBC_Mode::Encryption desCBCenc(pbSMMACKey, 8, pbIV);
desCBCenc.ProcessBlocks(pbDesOut, pbTestdata, 1);
CBC_Mode::Encryption desCBCEDE2enc;
desCBCEDE2enc.SetKeyWithIV(pbSMMACKey, 16, pbDesOut);
desCBCEDE2enc.ProcessBlocks(pbMACOutBuffer, pbTestdata+8, 1);

The correct result is: ff a1 75 fc 99 4b 79 6c


Do you have any Idea what I make wrong?

Additionaly I get an exception if I want to use the SetKeyWithIV for a
CBC_MAC object:
cbcMac.SetKeyWithIV(pbSMMACKey, 16, pbIV);

The exception is:
exception: CryptoPP::AlgorithmParametersBase::ParameterNotUsed

Thanks
regards
Alexander
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