jarsigner -keystore ./genkey.jks -signedjar ./signed.apk ./unsigned.apk business
输入密钥库的密码短语: //123123
输入business的密钥口令: //123456
jar 已签名。

   signingConfigs {
        config {
            storeFile file('../genkey.jks')
            storePassword '123123'
            keyAlias "business"
            keyPassword '123456'
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            signingConfig signingConfigs.config
        }
    }

Verified using v1 scheme (JAR signing): false
Verified using v2 scheme (APK Signature Scheme v2): true
Verified using v3 scheme (APK Signature Scheme v3): false
Number of signers: 1

Variant: release
Config: config
Store: D:\code\1.gitee\AndroidSignKeyConvert\genkey.jks
Alias: business
MD5: 9F:E0:78:DD:BC:2A:C2:FB:90:8D:67:D1:F7:FE:29:BF
SHA1: CC:A0:52:3A:4A:6F:0A:77:3A:68:2C:A0:18:52:1D:A7:36:EB:B5:16
SHA-256: A3:F7:B3:7E:3F:C0:E6:A8:FF:74:2C:4E:FA:FC:AC:66:E4:38:B3:02:2C:94:7E:07:AC:63:B2:0F:30:7F:09:51
Valid until: 2348年10月13日 星期三

keytool -importkeystore -srckeystore ./genkey.jks -srcstoretype JKS -deststoretype PKCS12 -destkeystore genkey.p12
输入目标密钥库口令://123456
再次输入新口令://123456
输入源密钥库口令://123123
输入 <business> 的密钥口令 //123456
已成功导入别名 business 的条目。
已完成导入命令: 1 个条目成功导入, 0 个条目失败或取消

keytool -v -importkeystore -srckeystore ./genkey.p12 -srcstoretype PKCS12 -destkeystore ./genkey.keystore -deststoretype JKS
输入目标密钥库口令://123123
再次输入新口令://123123
输入源密钥库口令://123456
已成功导入别名 business 的条目。
已完成导入命令: 1 个条目成功导入, 0 个条目失败或取消
[正在存储./genkey.keystore]

keytool -list -v -keystore genkey.jks
keytool -list -v -keystore genkey.keystore

openssl pkcs12 -in genkey.p12 -nodes -out genkey.rsa.pem
Enter Import Password: //参考如上5.1 p12的密码123456

用文本编辑器打开 genkey.rsa.pem，将从
-----BEGIN PRIVATE KEY-----
 到
-----END PRIVATE KEY-----
这一段（包含这两个tag）的文本复制出来，新建为文件 genkey_private.rsa.pem
将从
-----BEGIN CERTIFICATE-----
到
-----END CERTIFICATE-----
这一段（包含这两个tag）的文本复制出来，新建为文件 genkey.x509.pem （签名时用到的公钥）

public String getAppSign() {
    String result = null;
    PackageManager packageManager = getPackageManager();
    try {
        PackageInfo packageInfo = packageManager.getPackageInfo(
                   getPackageName(), PackageManager.GET_SIGNATURES);
        if (packageInfo == null) {
            return null;
        }
        Signature[] signatures = packageInfo.signatures;
        if (signatures == null || signatures.length < 1) {
            return null;
        }
        Signature signature = signatures[0];

        MessageDigest messageDigest = MessageDigest.getInstance("MD5");
        //messageDigest = MessageDigest.getInstance("SHA-1");

        //取MD5的值并转String
        byte[] md5Bytes = messageDigest.digest(signature.toByteArray());

        //对生成的16字节数组进行补零操作
        StringBuilder md5 = new StringBuilder(md5Bytes.length * 2);
        for (byte b : md5Bytes) {
            if ((b & 0xFF) < 0x10) {
                md5.append("0");
            }
            md5.append(Integer.toHexString(b & 0xFF));
        }

        result = md5.toString();
    } catch (Exception e) {
        e.printStackTrace();
    }

    Log.d("getAppSign", "getAppSign result:" + result);
    return result;
}