TDES CMAC algorithm for JCOP smart card

[smartycardpants]

I am looking for a Javacard code snippet that produces a known answer for a
TDES CMAC equal to the known answers in NISP SP 800-38B for the Two Key
TDEA (D.5, p.18) example. What I have done so far is reproduce the CIPH
subkey. I have been able to get the CIPH subkey using either the Cipher or
the Signature class. So, I'm part way there. I need to reproduce the T
values now. Does anybody have something that works?

Here is the current code snippet I wrote:

public byte[] computeCMAC() {

// 4c f1 51 34 a2 85 0d d5 8a 3d 10 ba 80 57 0d 38 4c f1 51 34 a2 85 0d d5

final byte[] KEYS_2 = {
(byte)0x4c,(byte)0xf1,(byte)0x51,(byte)0x34,
(byte)0xa2,(byte)0x85,(byte)0x0d,(byte)0xd5,
(byte)0x8a,(byte)0x3d,(byte)0x10,(byte)0xba,
(byte)0x80,(byte)0x57,(byte)0x0d,(byte)0x38};

tdesKey2 = (DESKey) KeyBuilder.buildKey(KeyBuilder.TYPE_DES,(short)128,false);

tdesKey2.setKey(KEYS_2, (short)0);

tdesC = Cipher.getInstance(Cipher.ALG_DES_CBC_ISO9797_M1, false);

cmacVP = new byte[32];

byte[] output = new byte[32];

tdesC.init(tdesKey2, Cipher.MODE_ENCRYPT);

short cmacLen = tdesC.update(null,(short)0,(short)0, output,(short)0);

cmacLen += tdesC.doFinal(output, (short)0, cmacLen, cmacVP, (short)0);

return cmacVP;

}


This produces the following of which the first 8 bytes matches the CIPH
subkey in NIST SP 800-38B:

C7 67 9B 9F 6B 8D 7D 7A 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

I am not sure what to do next to get the T value for an empty string.

[UNKNwYSHSA]

Step1: K => K1, K2
Step2: M, K, K1, K2 => CMAC

Next step: Geneate K1 and K2;

[UNKNwYSHSA]

Details:

Code: Select all

Step1 (k => ciph(0000000000000000)):
    Key: 4CF15134A2850DD5 8A3D10BA80570D38
    m: 0000000000000000
    s: C7679B9F6B8D7D7A

Step2: ciph(0000000000000000) => k1, k2:
    (MSB(s) == 1) => true
    L << 1
        (C7679B9F6B8D7D7A << 1) => 018ECF373ED71AFAF4 => 8ECF373ED71AFAF4
    K1 = (L << 1) | Rb
        8ECF373ED71AFAF4 XOR 000000000000001B => 8ECF373ED71AFAEF
    K1 << 1
        (8ECF373ED71AFAEF << 1) => 011D9E6E7DAE35F5DE => 1D9E6E7DAE35F5DE
    K2 = (K1 << 1) | Rb
        (1D9E6E7DAE35F5DE) XOR 000000000000001B => 1D9E6E7DAE35F5C5
 
 Step3: K, m, K1, K2 => T
     K: 4CF15134A2850DD5 8A3D10BA80570D38
     m: (empty string)
     K1: 8ECF373ED71AFAEF
     K2: 1D9E6E7DAE35F5C5
     
     M1 = K2 XOR (M1* || 10j)
         M1 = K2 XOR 8000000000000000 => 9D9E6E7DAE35F5C5
         C0 XOR M1 => 0000000000000000 XOR 9D9E6E7DAE35F5C5 => 9D9E6E7DAE35F5C5 
         C1 = CIPH_k_(C0 XOR M1) => BD2EBF9A3BA00361
         T = BD2EBF9A3BA00361

[smartycardpants]

Thank you! I coded that up and got the known answer.

[UNKNwYSHSA]

OK.