Vincent,
The CBC is explained in FIPS publication #81 and there
is a new document for 3DES version of it.
I'm not aware of how to do with Crypto lib but I did
this with just pure c++ using a standard DES engine.
I'm trying to do the same with Crypto.
Thanks
Tim
--- "Vincent Richomme @Tricubes" <[EMAIL PROTECTED]>
wrote:
> I am currently trying to developp an application
> using a Gemplus smart card (GPK 16000) and I am
> supposed to use what they call Secure Messaging to
> dialog with the card.
>
> The problem is my cryptographic background is very
> low and even with the examples my mind is still
> confufed.
>
> So everytime is send a command to the smart card I
> need to calculate a Crypto checksum as shown below :
>
>
>
> Imagine the Cmd is 24 bytes long, the first step is
> to divided it into blocks of 8 bytes :
>
>
>
>
>
>
>
>
>
> So in my case with my command of 24 bytes I obtain 3
> blocks : Block 1, Block and Block 3. And now here is
> how is calculated the checksum :
>
>
>
> Kts is a private key (16 bytes long) :
>
>
>
> R1 = 3DES(Block1, Kts)
>
> R2 = 3DES(Block2 XOR R1, Kts)
>
> R3 = 3DES (Block3 XOR R2, Kts)
>
>
>
> And my checksum is supposed to be the latest result
> R3.
>
> Now my question is how do I do that ?
>
> I have another question when you do a 3DES with a
> private key of 16 bytes and a text to cipher of 8
> bytes what is the length of the ciphered text ? (8
> or 16).
>
> After having read some tutorial on 3DES, it seems
> that this kind of algorithm is actually implemented
> in 3DES CBC mode but I am not sure of that. Anyway I
> tried the following code :
>
>
>
> // 3DES in CBC mode with Kats
>
> unsigned int outputLength;
>
> const byte iv[] =
> {0x12,0x34,0x56,0x78,0x90,0xab,0xcd,0xef};
>
> byte* ciphertext;
>
>
>
> CBC_Mode<DES_EDE2>::Encryption
> cbcEncryption(m_Kats,DES_EDE2::DEFAULT_KEYLENGTH,
> iv);
>
> StreamTransformationFilter
>
encryptor(cbcEncryption,NULL,StreamTransformationFilter::NO_PADDING);
>
> encryptor.Put(Cmd, 24);
>
> encryptor.MessageEnd();
>
> outputLength =
> encryptor.MaxRetrievable();
>
> ciphertext = new byte[outputLength];
>
> encryptor.Get(ciphertext, outputLength);
>
>
>
> I don't even know what is the IV tab but I finally
> obtain a 24 bytes long ciphered text and I was more
> expected a 8 bytes result. To sum up I am lost.
> Please Help
>
>
>
>
>
>
>
>
>
>
>
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>
>
>
>
>
>
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