func Signature(payload string, privateKey string) (interface{}, error) {

    decoded, _ := pem.Decode([]byte(privateKey))

    if decoded == nil {

        return nil, errors.New("decoded private key error")

    }

​

    hash := md5.New()

    hash.Write([]byte(payload))

    hashed := hash.Sum(nil)

​

    rsaPrivateKey, err := x509.ParsePKCS1PrivateKey(decoded.Bytes)

    if err != nil {

        return nil, err

    }

​

    signature, err := rsa.SignPKCS1v15(rand.Reader, rsaPrivateKey, crypto.MD5, hashed)

    if err != nil {

        return nil, err

    }

​

    if err := rsa.VerifyPKCS1v15(&rsaPrivateKey.PublicKey, crypto.MD5, hashed, signature); err != nil {

        return nil, err

    }

​

    encoded := hex.EncodeToString(signature)

    return encoded, nil

}