Apple eciesEncryptionCofactorVariableIVX963SHA256AESGCM与BouncyCastle ECCDHwithSHA256KDF

问题描述

我正在尝试使用Apple算法BouncyCastle对Java（eciesEncryptionCofactorVariableIVX963SHA256AESGCM）和iOS之间的通信进行加密。

Apple的算法没有很好的文档，但是我发现this article很有帮助。

我还在BouncyCastle documentation中发现了以下算法，该算法似乎与我要寻找的算法很接近：

• ECCDHwithSHA256KDF代表使用X9.63 KDF和SHA256作为PRF的EC辅因子DH

package com.example.ios.encryption;

import org.bouncycastle.jce.ECNamedCurveTable;
import org.bouncycastle.jce.ECPointUtil;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.jce.spec.ECNamedCurveSpec;
import org.bouncycastle.jce.spec.ECParameterSpec;
import org.bouncycastle.util.encoders.Base64;

import java.math.BigInteger;
import java.security.*;
import java.security.spec.ECPoint;
import java.security.spec.ECPrivateKeySpec;
import java.security.spec.ECPublicKeySpec;
import java.util.Arrays;

import javax.crypto.Cipher;
import javax.crypto.KeyAgreement;
import javax.crypto.SecretKey;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class IOSEncryptionECwithAES {

    public void testDecrypt() {

        // Receiver EC Public Key
        String pubKeyBase64 = "BBPT50Rn0PeeV0LxUbhDV7U1FUgVw9YLVctQx5HA+TiA3lp3k/cud8Xsjh6lytgaI5S7IUW1YouUiPNR/7LPArk=";
        PublicKey pubKey = getPublicKey(Base64.decode(pubKeyBase64));
        
        // Receiver EC Private Key
        String privateKeyBase64 = "BBPT50Rn0PeeV0LxUbhDV7U1FUgVw9YLVctQx5HA+TiA3lp3k/cud8Xsjh6lytgaI5S7IUW1YouUiPNR/7LPArkWcIYOQWtdkbTqmy++lz0cQ8ukWvUyhD9yzqZHPLQgQg==";
        PrivateKey privateKey = getPrivateKey(Base64.decode(privateKeyBase64));
    
        // Encrypted data
        String iosOutputBase64 = "BNNzHjSJQxP8jNuj5W9XSW0XNgpOlEHY/S4KzZQJFxwjzoujuwz5kJeOLj6cASBaYKePGLhkbE0qN20y8aHpU+PmeuDJWY7LZ25LjvutafOJGugdRZdURRwFSke7hzhXlSneaTFegT3xOoq9ffjCynwD7iRD";
        byte[] iosOutput = Base64.decode(iosOutputBase64);

        // Plaintext is a random UUID
        String plainText = "514227F0-51E9-41AC-9A39-42752E2ABADF";

        byte[] decryptedData = decryptEciesEncryptionCofactorVariableIVX963SHA256AESGCM(privateKey,iosOutput);
        System.out.println(new String(decryptedData));
    }

    public byte[] decryptEciesEncryptionCofactorVariableIVX963SHA256AESGCM(PrivateKey privateKey,byte[] iosOutput) throws Exception {

        // 1. Take ephemeral public key
        byte[] ephemeralKeyBytes = Arrays.copyOfRange(iosOutput,65);
        PublicKey ephemeralPublicKey = getPublicKey(ephemeralKeyBytes);
        byte[] encryptedData = Arrays.copyOfRange(iosOutput,65,iosOutput.length);

        // 2. Key agreement using ECDH with Cofactor and integrated X9.63 
        byte[] kdfOut = getSharedSecret(ephemeralPublicKey,privateKey);

        byte[] secretKeyBytes = Arrays.copyOfRange(kdfOut,16);
        SecretKey secretKey = new SecretKeySpec(secretKeyBytes,"AES");

        // 4. Decrypt with AES key
        int tagLength = 128;
        byte[] iv = Arrays.copyOfRange(kdfOut,16,kdfOut.length);
        GCMParameterSpec aesGcmParams = new GCMParameterSpec(tagLength,iv);
        Cipher c = Cipher.getInstance("AES/GCM/NoPadding");
        c.init(Cipher.DECRYPT_MODE,secretKey,aesGcmParams);
        byte[] decryptedData = c.doFinal(encryptedData);

        return decryptedData;
    }

    /**
     * Convert uncompressed public key into PublicKey using BouncyCastle
     * For an elliptic curve public key,the format follows the ANSI X9.63 standard
     * using a byte string of 04 || X || Y
     *
     * @param encodedBytes raw bytes received
     * @return the Elliptic-Curve Public Key based on curve SECP256R1
     */
    private PublicKey getPublicKey(byte[] encodedBytes) throws Exception {
        KeyFactory keyFactory = KeyFactory.getInstance("EC");
        ECParameterSpec ecParameterSpec = ECNamedCurveTable.getParameterSpec("secp256r1");
        ECNamedCurveSpec params = new ECNamedCurveSpec("secp256r1",ecParameterSpec.getCurve(),ecParameterSpec.getG(),ecParameterSpec.getN());
        ECPoint publicPoint =  ECPointUtil.decodePoint(params.getCurve(),encodedBytes);
        ECPublicKeySpec pubKeySpec = new ECPublicKeySpec(publicPoint,params);
        return keyFactory.generatePublic(pubKeySpec);
    }

  /**
   * Convert private key for external output from iOS
   * For an elliptic curve private key,the output is formatted as the public key
   * concatenated with the big endian encoding of the secret scalar,or 04 || X || Y || K.
   *
   * @param encodedBytes raw bytes received
   * @return the Elliptic-Curve Private Key based on curve SECP256R1
   */
  private PrivateKey getPrivateKey(byte[] encodedBytes) throws Exception {
        BigInteger s = new BigInteger(Arrays.copyOfRange(encodedBytes,encodedBytes.length));
        ECParameterSpec ecParameterSpec = ECNamedCurveTable.getParameterSpec("secp256r1");
        ECNamedCurveSpec params = new ECNamedCurveSpec("secp256r1",ecParameterSpec.getN());
        ECPrivateKeySpec privateKeySpec = new ECPrivateKeySpec(s,params);
        KeyFactory keyFactory = KeyFactory.getInstance("EC");
        return keyFactory.generatePrivate(privateKeySpec);
  }

  /**
   * Key agreement using ECDH with Cofactor and integrated X9.63 KDF SHA-256
   * 
   * @param ephemeralPublicKey created by the sender
   * @param privateKey from the receiver
   * @return shared secret of 32-bytes containing the 128-bit AES key and 16-byte IV
   */
   private byte[] getSharedSecret(PublicKey ephemeralPublicKey,PrivateKey privateKey) throws Exception {
      String keyAgreementAlgorithm = "ECCDHwithSHA256KDF";
      KeyAgreement keyAgreement = KeyAgreement.getInstance(keyAgreementAlgorithm,new BouncyCastleProvider());
      keyAgreement.init(privateKey);
      keyAgreement.doPhase(ephemeralPublicKey,true);
      return keyAgreement.generateSecret();
  }
}

不幸的是，这不起作用，并导致异常。

javax.crypto.AEADBadTagException: Tag mismatch!

    at java.base/com.sun.crypto.provider.NativeGaloisCounterMode.decryptFinal(NativeGaloisCounterMode.java:454)

我想念什么？可以通过较小的修改来修复此代码吗？

解决方法

我确实通过使用O2 Czech Republic中的代码使它成功了，但是确实有效，但是该代码是2017年的，我希望现在可以用更少的代码完成这些工作。版本的BouncyCastle。

请参阅下面的工作代码。它将KeyAgreement和KeyDerivationFunction分为两个单独的函数。

   /**
     * Key agreement using ECDH with Cofactor and integrated X9.63 KDF SHA-256
     *
     * @param ephemeralPublicKey created by the sender
     * @param privateKey from the receiver
     * @return shared secret of 32-bytes containing the 128-bit AES key and 16-byte IV
     */
    private byte[] getInitialSecret(PublicKey ephemeralPublicKey,PrivateKey privateKey) throws Exception {
        String keyAgreementAlgorithm = "ECCDH"; // Seems to be equivalent to "ECDHC"
        KeyAgreement keyAgreement = KeyAgreement.getInstance(keyAgreementAlgorithm,new BouncyCastleProvider());
        keyAgreement.init(privateKey);
        keyAgreement.doPhase(ephemeralPublicKey,true);
        return keyAgreement.generateSecret();
    }

    /**
     * Derive actual SecretKey with X9.63 KDF SHA-256
     *
     * @param initialSecret output from the ECDH agreement with Cofactor
     * @param ephemeralKeyBytes emphemeral public key from sender
     * @return shared secret of 32-bytes containing the 128-bit AES key and 16-byte IV
     */
    private byte[] getDerivation(byte[] initialSecret,byte[] ephemeralKeyBytes) {
        KDF2BytesGenerator kdfGenerator = new KDF2BytesGenerator(new SHA256Digest());
        kdfGenerator.init(new KDFParameters(initialSecret,ephemeralKeyBytes));
        byte[] kdfOut = new byte[32]; 
        kdfGenerator.generateBytes(kdfOut,32);
        return kdfOut;
    }
  }

并更改

byte[] kdfOut = getSharedSecret(ephemeralPublicKey,privateKey);

进入

byte[] initialSecret = getInitialSecret(ephemeralPublicKey,privateKey);
byte[] kdfOut = getDerivation(initialSecret,ephemeralKeyBytes);