diff --git a/Cargo.lock b/Cargo.lock
index 6b4e29f..e0fd4b0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -296,7 +296,7 @@ version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1b391911b9a786312a10cb9d2b3d0735adfd5a8113eb3648de26a75e91b0826c"
 dependencies = [
- "rand",
+ "rand 0.7.3",
 ]
 
 [[package]]
@@ -482,7 +482,18 @@ checksum = "fc587bc0ec293155d5bfa6b9891ec18a1e330c234f896ea47fbada4cadbe47e6"
 dependencies = [
  "cfg-if 0.1.10",
  "libc",
- "wasi",
+ "wasi 0.9.0+wasi-snapshot-preview1",
+]
+
+[[package]]
+name = "getrandom"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c9495705279e7140bf035dde1f6e750c162df8b625267cd52cc44e0b156732c8"
+dependencies = [
+ "cfg-if 1.0.0",
+ "libc",
+ "wasi 0.10.2+wasi-snapshot-preview1",
 ]
 
 [[package]]
@@ -519,7 +530,7 @@ dependencies = [
  "protobuf",
  "protobuf-codegen-pure",
  "quinn",
- "rand",
+ "rand 0.7.3",
  "regex",
  "serde",
  "serde_derive",
@@ -545,6 +556,7 @@ dependencies = [
  "mac_address",
  "machine-uid",
  "minreq",
+ "rand 0.8.3",
  "rocksdb",
  "rust-ini",
  "serde",
@@ -1014,7 +1026,7 @@ dependencies = [
  "bytes",
  "ct-logs",
  "err-derive",
- "rand",
+ "rand 0.7.3",
  "ring",
  "rustls",
  "rustls-native-certs",
@@ -1038,11 +1050,23 @@ version = "0.7.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6a6b1679d49b24bbfe0c803429aa1874472f50d9b363131f0e89fc356b544d03"
 dependencies = [
- "getrandom",
+ "getrandom 0.1.15",
  "libc",
- "rand_chacha",
- "rand_core",
- "rand_hc",
+ "rand_chacha 0.2.2",
+ "rand_core 0.5.1",
+ "rand_hc 0.2.0",
+]
+
+[[package]]
+name = "rand"
+version = "0.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ef9e7e66b4468674bfcb0c81af8b7fa0bb154fa9f28eb840da5c447baeb8d7e"
+dependencies = [
+ "libc",
+ "rand_chacha 0.3.0",
+ "rand_core 0.6.2",
+ "rand_hc 0.3.0",
 ]
 
 [[package]]
@@ -1052,7 +1076,17 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f4c8ed856279c9737206bf725bf36935d8666ead7aa69b52be55af369d193402"
 dependencies = [
  "ppv-lite86",
- "rand_core",
+ "rand_core 0.5.1",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e12735cf05c9e10bf21534da50a147b924d555dc7a547c42e6bb2d5b6017ae0d"
+dependencies = [
+ "ppv-lite86",
+ "rand_core 0.6.2",
 ]
 
 [[package]]
@@ -1061,7 +1095,16 @@ version = "0.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "90bde5296fc891b0cef12a6d03ddccc162ce7b2aff54160af9338f8d40df6d19"
 dependencies = [
- "getrandom",
+ "getrandom 0.1.15",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.6.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34cf66eb183df1c5876e2dcf6b13d57340741e8dc255b48e40a26de954d06ae7"
+dependencies = [
+ "getrandom 0.2.2",
 ]
 
 [[package]]
@@ -1070,7 +1113,16 @@ version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ca3129af7b92a17112d59ad498c6f81eaf463253766b90396d39ea7a39d6613c"
 dependencies = [
- "rand_core",
+ "rand_core 0.5.1",
+]
+
+[[package]]
+name = "rand_hc"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3190ef7066a446f2e7f42e239d161e905420ccab01eb967c9eb27d21b2322a73"
+dependencies = [
+ "rand_core 0.6.2",
 ]
 
 [[package]]
@@ -1085,7 +1137,7 @@ version = "0.3.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "de0737333e7a9502c789a36d7c7fa6092a49895d4faa31ca5df163857ded2e9d"
 dependencies = [
- "getrandom",
+ "getrandom 0.1.15",
  "redox_syscall",
  "rust-argon2",
 ]
@@ -1502,6 +1554,12 @@ version = "0.9.0+wasi-snapshot-preview1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cccddf32554fecc6acb585f82a32a72e28b48f8c4c1883ddfeeeaa96f7d8e519"
 
+[[package]]
+name = "wasi"
+version = "0.10.2+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fd6fbd9a79829dd1ad0cc20627bf1ed606756a7f77edff7b66b7064f9cb327c6"
+
 [[package]]
 name = "wasm-bindgen"
 version = "0.2.68"
diff --git a/Cargo.toml b/Cargo.toml
index f48d688..2ee84bd 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -25,6 +25,7 @@ mac_address = "1.1"
 whoami = "0.9"
 base64 = "0.13"
 cryptoxide = "0.3"
+rand = "0.8"
 
 [build-dependencies]
 hbb_common = { path = "libs/hbb_common" }
diff --git a/src/lic.rs b/src/lic.rs
index 68cf5f3..6b7b78e 100644
--- a/src/lic.rs
+++ b/src/lic.rs
@@ -2,6 +2,7 @@ use hbb_common::{bail, log, ResultType};
 use serde_derive::{Deserialize, Serialize};
 use std::io::prelude::*;
 use std::path::Path;
+use rand::Rng;
 
 #[derive(Debug, PartialEq, Default, Serialize, Deserialize, Clone)]
 pub struct Machine {
@@ -25,6 +26,8 @@ pub struct Post {
     version: String,
     #[serde(default)]
     next_check_time: u64,
+    #[serde(default)]
+    nonce: String,
 }
 
 const LICENSE_FILE: &'static str = ".license.txt";
@@ -90,12 +93,16 @@ fn write_lic(lic: &str) {
 
 fn check_email(machine: String, email: String, version: String) -> ResultType<u64> {
     log::info!("Checking email with the license server ...");
+    let mut rng = rand::thread_rng();
+    let nonce: usize = rng.gen();
+    let nonce = nonce.to_string();
     let resp = minreq::post("http://rustdesk.com/api/check-email")
         .with_body(
             serde_json::to_string(&Post {
                 machine: machine.clone(),
                 version,
                 email,
+                nonce: nonce.clone(),
                 ..Default::default()
             })
             .unwrap(),
@@ -106,10 +113,15 @@ fn check_email(machine: String, email: String, version: String) -> ResultType<u6
         if !p.status.is_empty() {
             bail!("{}", p.status);
         }
-        if !verify(&p.machine, &machine) {
+        if !verify(&p.nonce, &nonce) {
             bail!("Verification failure");
         }
-        write_lic(&p.machine);
+        if !machine.is_empty() {
+            if !verify(&p.machine, &machine) {
+                bail!("Verification failure");
+            }
+            write_lic(&p.machine);
+        }
         log::info!("License OK");
         let mut wait = p.next_check_time;
         if wait == 0 {