Mifare火灾的MAC和CMAC计算

Question

有人能帮我指导Mifare Desfire的MAC(4字节)和CMAC(8字节)的计算吗？我得到了意想不到的结果。

Deskey      =   0000000000000000
Block1(B1)  =   1122334455667788
Block2(B2)  =   9900112200000000
IV          =   0000000000000000
sessionkey  =   2923be84b1495461


R1 = Enc(B1 xor IV)         f2f13994d24714ca
R2 = Enc(R1 xor B2)         880fe38ab9e8a8d3
MAC   880fe38a

Expected MAC =  c8d70ad2 95a88a36

CMAC结果

AESKey          =       00000000000000000000000000000000
Block           =       000102030405060708090a0b0c0d0e0f
Enc(Block)      =       7aca0fd9bcd6ec7c9f97466616e6a282
SubKey1         =       CDD297A9DF1458771099F4B39468565C
SubKey2         =       9BA52F53BE28B0EE2133E96728D0AC3F
CMAC(16bytes)   =       8A57896F795CB6ABF6867DAD41A5FB15

CMAC只由DES生成，TDES像DES一样加密除最终块之外的所有块，在零售MAC计算中应该加密TDES吗？

Answer 1

在MAC计算方面，它似乎是3 3DES模式的数据加密，明文上填充为零，而V4为零。3 3DES密钥由XORing创建，会话密钥为24 0字节。以下是Java中的一个示例：

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.DESedeKeySpec;
import javax.crypto.spec.IvParameterSpec;
import javax.xml.bind.DatatypeConverter;

public class MACTest {

  public static void main(String[] args) throws Exception {

    final byte[] keyBytes = new byte[24];
    final byte[] paddedPlaintext = 
        hexStringToByteArray("11223344556677889900112200000000");
    final byte[] iv = new byte[8];
    final byte[] sessionKeyBytes = hexStringToByteArray("2923be84b1495461");

    final byte[] derivedKeyBytes = new byte[24];
    for (int i = 0; i < sessionKeyBytes.length; i++) {
      derivedKeyBytes[i] = (byte) (keyBytes[i] ^ sessionKeyBytes[i]);
    }

    System.out.println(toHexString(derivedKeyBytes));
    SecretKeyFactory factory = SecretKeyFactory.getInstance("DESede");
    SecretKey derivedKey = factory.generateSecret(new DESedeKeySpec(
        derivedKeyBytes));

    Cipher c = Cipher.getInstance("DESede/CBC/NoPadding");
    c.init(Cipher.ENCRYPT_MODE, derivedKey, new IvParameterSpec(iv));
    byte[] result = c.doFinal(paddedPlaintext);
    System.out.println(toHexString(result));
  }

  public static String toHexString(byte[] array) {
    return DatatypeConverter.printHexBinary(array);
  }

  public static byte[] hexStringToByteArray(String s) {
    return DatatypeConverter.parseHexBinary(s);
  }
}

输出：

2923BE84B149546100000000000000000000000000000000
F2F13994D24714CA880FE38AB9E8A8D3

您没有提供足够的信息来理解计算AES CMAC示例所需的内容，也不了解您的实际问题是什么。大概你没有得到预期的结果吧？