根据《分组密码操作模式建议书:Galois/Counter Mode (GCM) and GMAC》的第 5.2 节(两个 GCM 功能) ,它提到对于 GMAC 的情况,经过身份验证的加密和解密函数成为生成和解密的函数。验证非机密数据上的身份验证标签。
在网上和 JCA 参考页面上查看,我知道 GMAC 是这样生成的:
Cipher cipher = Cipher.getInstance("AES/GCM/PKCS5Padding");
cipher.init(ENCRYPT_MODE, encryptionKey, new GCMParameterSpec(96, iv), new SecureRandom());
cipher.updateAAD(aadData);
byte[] gmac = cipher.doFinal();
但是,我对 GMAC 验证有疑问。这是验证 GMAC 的正确方法吗?
Cipher decryptCipher = Cipher.getInstance("AES/GCM/PKCS5Padding");
decryptCipher.init(DECRYPT_MODE, encryptionKey, new GCMParameterSpec(96, iv), new SecureRandom());
decryptCipher.updateAAD(aadData);
decryptCipher.update(gmac);
byte[] verifiedGmac = decryptCipher.doFinal();
哪里验证Gmac大小== 0?
这是带有输入和输出的完整代码:
import org.hamcrest.core.Is;
import org.junit.Test;
import javax.crypto.Cipher;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.security.SecureRandom;
import static javax.crypto.Cipher.DECRYPT_MODE;
import static javax.crypto.Cipher.ENCRYPT_MODE;
import static javax.xml.bind.DatatypeConverter.parseHexBinary;
import static javax.xml.bind.DatatypeConverter.printHexBinary;
import static org.junit.Assert.assertThat;
public class TestGmac {
@Test
public void generateAndVerifyGmac() throws Exception {
final byte[] message = parseHexBinary("AAAAAAAAAAAA");
final byte[] authenticatedKey = parseHexBinary("63509E5A672C092CAD0B1DC6CE009A61");
final byte[] aadData = buildAadForAuthenticationOnly(message, authenticatedKey);
final byte[] iv = parseHexBinary("BBBBBBBBBBBBBBBBBBBBBBBB");
SecretKeySpec encryptionKey = new SecretKeySpec(parseHexBinary("55804F3AEB4E914DC91255944A1F565A"), "AES");
// Generate GMAC
Cipher cipher = Cipher.getInstance("AES/GCM/PKCS5Padding");
cipher.init(ENCRYPT_MODE, encryptionKey, new GCMParameterSpec(96, iv), new SecureRandom());
cipher.updateAAD(aadData);
byte[] gmac = cipher.doFinal();
assertThat(printHexBinary(gmac), Is.is("44C955D63799428524E97993"));
// Verify GMAC
Cipher decryptCipher = Cipher.getInstance("AES/GCM/PKCS5Padding");
decryptCipher.init(DECRYPT_MODE, encryptionKey, new GCMParameterSpec(96, iv), new SecureRandom());
decryptCipher.updateAAD(aadData);
decryptCipher.update(gmac);
byte[] verifiedGmac = decryptCipher.doFinal();
assertThat(printHexBinary(verifiedGmac), Is.is(""));
}
private byte[] buildAadForAuthenticationOnly(byte[] message, byte[] authenticatedKey) throws IOException {
ByteArrayOutputStream aaDoutputStream = new ByteArrayOutputStream();
aaDoutputStream.write(parseHexBinary("10"));
aaDoutputStream.write(authenticatedKey);
aaDoutputStream.write(message);
return aaDoutputStream.toByteArray();
}
}