解密步骤如下：

（1）对加密串A做base64解码，得到加密串B

（2）对商户key做md5，得到32位小写key* ( key设置路径：微信商户平台(pay.weixin.qq.com)-->账户设置-->API安全-->密钥设置 )

（3）用key*对加密串B做AES-256-ECB解密（PKCS7Padding）

<dependency><groupId>org.bouncycastle</groupId><artifactId>bcprov-ext-jdk16</artifactId><version>1.45</version></dependency>

import javax.crypto.Cipher;import javax.crypto.spec.IvParameterSpec;import javax.crypto.spec.SecretKeySpec;import java.security.AlgorithmParameters;import java.security.MessageDigest;import java.security.Security;import java.util.Base64;

public class AESUtil {

/** * 密钥算法 */ private static final String ALGORITHM = "AES";/** * 加解密算法/工作模式/填充方式 */ private static final String ALGORITHM_MODE_PADDING = "AES/ECB/PKCS7Padding";

/** * AES解密 * * @param base64Data * @return * @throws Exception */ public static String decryptData(String base64Data,String lowMad5Key) throws Exception { SecretKeySpec key = new SecretKeySpec(lowMad5Key.getBytes(), ALGORITHM); Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider()); Cipher cipher = Cipher.getInstance(ALGORITHM_MODE_PADDING); cipher.init(Cipher.DECRYPT_MODE, key); Base64.Decoder decoder = Base64.getDecoder(); String newData= new String(decoder.decode(base64Data), "ISO-8859-1");return new String(cipher.doFinal(newData.getBytes("ISO-8859-1")), "utf-8"); }public static String MD5(String data) throws Exception { MessageDigest md = MessageDigest.getInstance("MD5");byte[] array = md.digest(data.getBytes("UTF-8")); StringBuilder sb = new StringBuilder();byte[] var4 = array;int var5 = array.length;

for(int var6 = 0; var6 < var5; ++var6) {byte item = var4[var6]; sb.append(Integer.toHexString(item & 255 | 256).substring(1, 3)); }

return sb.toString().toUpperCase(); }

public static void main(String[] args) throws Exception { String a = "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"; String ab = AESUtil.decryptData(a,AESUtil.MD5("4567qwer53321ty444rewq87656uyt").toLowerCase()); System.out.println(ab); }

结果：========================================

<root><out_refund_no><![CDATA[23003134]]></out_refund_no><out_trade_no><![CDATA[23003125]]></out_trade_no><refund_account><![CDATA[REFUND_SOURCE_RECHARGE_FUNDS]]></refund_account><refund_fee><![CDATA[10]]></refund_fee><refund_id><![CDATA[240000209102018121407497402648]]></refund_id><refund_recv_accout><![CDATA[支付用户零钱]]></refund_recv_accout><refund_request_source><![CDATA[API]]></refund_request_source><refund_status><![CDATA[SUCCESS]]></refund_status><settlement_refund_fee><![CDATA[10]]></settlement_refund_fee><settlement_total_fee><![CDATA[11]]></settlement_total_fee><success_time><![CDATA[2018-12-14 11:25:58]]></success_time><total_fee><![CDATA[11]]></total_fee><transaction_id><![CDATA[3200000234201812136388015826]]></transaction_id></root>

问题汇总：

Cannot find any provider supporting AES/ECB/PKCS7Padding

增加Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());

javax.crypto.BadPaddingException: pad block corrupted

秘钥不正确