diff --git a/README.md b/README.md
index 7cbe6f6b..bdd46a6f 100644
--- a/README.md
+++ b/README.md
@@ -258,6 +258,11 @@ Usage
        [-u]                       enable udprelay mode,
                                   TPROXY is required in redir mode
 
+       [-U]                       enable UDP relay and disable TCP relay,
+                                  not available in local mode
+
+       [-A]                       enable onetime authentication
+
        [-L <addr>:<port>]         specify destination server address and port
                                   for local port forwarding,
                                   only available in tunnel mode
diff --git a/shadowsocks-libev.8 b/shadowsocks-libev.8
index 252e6470..2bfe08e6 100644
--- a/shadowsocks-libev.8
+++ b/shadowsocks-libev.8
@@ -96,6 +96,9 @@ Setup the name servers for libudns. The default server is fetched from
 .B \-u
 Enable UDP relay.
 .TP
+.B \-A
+Enable onetime authentication.
+.TP
 .B \-v
 Enable verbose mode.
 .TP
diff --git a/src/encrypt.c b/src/encrypt.c
index fd404c07..b337817c 100644
--- a/src/encrypt.c
+++ b/src/encrypt.c
@@ -75,6 +75,7 @@
 
 static uint8_t *enc_table;
 static uint8_t *dec_table;
+static uint8_t auth_key[ONETIMEAUTH_KEYBYTES];
 static uint8_t enc_key[MAX_KEY_LENGTH];
 static int enc_key_len;
 static int enc_iv_len;
@@ -1026,6 +1027,14 @@ static int cipher_context_update(cipher_ctx_t *ctx, uint8_t *output, int *olen,
 #endif
 }
 
+int ss_onetimeauth(char *auth, char *msg, int msg_len) {
+    return crypto_onetimeauth((uint8_t *)auth, (uint8_t *)msg, msg_len, auth_key);
+}
+
+int ss_onetimeauth_verify(char *auth, char *msg, int msg_len) {
+    return crypto_onetimeauth_verify((uint8_t *)auth, (uint8_t *)msg, msg_len, auth_key);
+}
+
 char * ss_encrypt_all(int buf_size, char *plaintext, ssize_t *len, int method)
 {
     if (method > TABLE) {
@@ -1446,6 +1455,7 @@ int enc_init(const char *pass, const char *method)
     } else {
         enc_key_init(m, pass);
     }
+    crypto_generichash(auth_key, ONETIMEAUTH_KEYBYTES, (uint8_t *)pass, strlen(pass), NULL, 0);
     return m;
 }
 
diff --git a/src/encrypt.h b/src/encrypt.h
index df20c3a5..9ee37527 100644
--- a/src/encrypt.h
+++ b/src/encrypt.h
@@ -140,6 +140,9 @@ typedef struct {
 #define SALSA20             15
 #define CHACHA20            16
 
+#define ONETIMEAUTH_BYTES 16U
+#define ONETIMEAUTH_KEYBYTES 32U
+
 #define min(a, b) (((a) < (b)) ? (a) : (b))
 #define max(a, b) (((a) > (b)) ? (a) : (b))
 
@@ -161,4 +164,7 @@ int enc_get_iv_len(void);
 void cipher_context_release(cipher_ctx_t *evp);
 unsigned char *enc_md5(const unsigned char *d, size_t n, unsigned char *md);
 
+int ss_onetimeauth(char *auth, char *msg, int msg_len);
+int ss_onetimeauth_verify(char *auth, char *msg, int msg_len);
+
 #endif // _ENCRYPT_H
diff --git a/src/local.c b/src/local.c
index c0388949..6ca85baa 100644
--- a/src/local.c
+++ b/src/local.c
@@ -94,6 +94,8 @@ static int nofile = 0;
 #endif
 #endif
 
+static int auth = 0;
+
 static void server_recv_cb(EV_P_ ev_io *w, int revents);
 static void server_send_cb(EV_P_ ev_io *w, int revents);
 static void remote_recv_cb(EV_P_ ev_io *w, int revents);
@@ -470,6 +472,12 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
 
                 if (!remote->direct) {
                     memcpy(remote->buf, ss_addr_to_send, addr_len);
+
+                    if (auth) {
+                        ss_onetimeauth(remote->buf + addr_len, ss_addr_to_send, addr_len);
+                        addr_len += ONETIMEAUTH_BYTES;
+                    }
+
                     if (r > 0) {
                         memcpy(remote->buf + addr_len, buf, r);
                     }
@@ -921,10 +929,10 @@ int main(int argc, char **argv)
     USE_TTY();
 
 #ifdef ANDROID
-    while ((c = getopt_long(argc, argv, "f:s:p:l:k:t:m:i:c:b:a:uvV",
+    while ((c = getopt_long(argc, argv, "f:s:p:l:k:t:m:i:c:b:a:uvVA",
                             long_options, &option_index)) != -1) {
 #else
-    while ((c = getopt_long(argc, argv, "f:s:p:l:k:t:m:i:c:b:a:uv",
+    while ((c = getopt_long(argc, argv, "f:s:p:l:k:t:m:i:c:b:a:uvA",
                             long_options, &option_index)) != -1) {
 #endif
         switch (c) {
@@ -979,6 +987,10 @@ int main(int argc, char **argv)
         case 'v':
             verbose = 1;
             break;
+        case 'A':
+            auth = 1;
+            LOGI("onetime authentication enabled");
+            break;
 #ifdef ANDROID
         case 'V':
             vpn = 1;
diff --git a/src/redir.c b/src/redir.c
index 3fa2aee9..0fcfd0c3 100644
--- a/src/redir.c
+++ b/src/redir.c
@@ -83,6 +83,7 @@ static void close_and_free_server(EV_P_ struct server *server);
 int verbose = 0;
 
 static int mode = TCP_ONLY;
+static int auth = 0;
 
 int getdestaddr(int fd, struct sockaddr_storage *destaddr)
 {
@@ -376,6 +377,11 @@ static void remote_send_cb(EV_P_ ev_io *w, int revents)
                 return;
             }
 
+            if (auth) {
+                ss_onetimeauth(ss_addr_to_send + addr_len, ss_addr_to_send, addr_len);
+                addr_len += ONETIMEAUTH_BYTES;
+            }
+
             int s = send(remote->fd, ss_addr_to_send, addr_len, 0);
             free(ss_addr_to_send);
 
@@ -614,7 +620,7 @@ int main(int argc, char **argv)
 
     opterr = 0;
 
-    while ((c = getopt(argc, argv, "f:s:p:l:k:t:m:c:b:a:uUv")) != -1) {
+    while ((c = getopt(argc, argv, "f:s:p:l:k:t:m:c:b:a:uUvA")) != -1) {
         switch (c) {
         case 's':
             if (remote_num < MAX_REMOTE_NUM) {
@@ -659,6 +665,10 @@ int main(int argc, char **argv)
         case 'v':
             verbose = 1;
             break;
+        case 'A':
+            auth = 1;
+            LOGI("onetime authentication enabled");
+            break;
         }
     }
 
diff --git a/src/server.c b/src/server.c
index 3c7e29a2..c10b8665 100644
--- a/src/server.c
+++ b/src/server.c
@@ -109,6 +109,7 @@ int verbose = 0;
 
 static int acl = 0;
 static int mode = TCP_ONLY;
+static int auth = 0;
 
 static int fast_open = 0;
 #ifdef HAVE_SETRLIMIT
@@ -639,6 +640,16 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
 
         offset += 2;
 
+        if (auth) {
+            if (ss_onetimeauth_verify(server->buf + offset, server->buf, offset)) {
+                LOGE("authentication error %d", atyp);
+                report_addr(server->fd);
+                close_and_free_server(EV_A_ server);
+                return;
+            };
+            offset += ONETIMEAUTH_BYTES;
+        }
+
         if (verbose) {
             LOGI("connect to: %s:%d", host, ntohs(port));
         }
@@ -1193,7 +1204,7 @@ int main(int argc, char **argv)
 
     USE_TTY();
 
-    while ((c = getopt_long(argc, argv, "f:s:p:l:k:t:m:c:i:d:a:uUv",
+    while ((c = getopt_long(argc, argv, "f:s:p:l:k:t:m:c:i:d:a:uUvA",
                             long_options, &option_index)) != -1) {
         switch (c) {
         case 0:
@@ -1250,6 +1261,10 @@ int main(int argc, char **argv)
         case 'v':
             verbose = 1;
             break;
+        case 'A':
+            auth = 1;
+            LOGI("onetime authentication enabled");
+            break;
         }
     }
 
diff --git a/src/tunnel.c b/src/tunnel.c
index ee8b781a..d44a0e00 100644
--- a/src/tunnel.c
+++ b/src/tunnel.c
@@ -91,6 +91,7 @@ int vpn = 0;
 int verbose = 0;
 
 static int mode = TCP_ONLY;
+static int auth = 0;
 
 #ifndef __MINGW32__
 static int setnonblocking(int fd)
@@ -418,6 +419,11 @@ static void remote_send_cb(EV_P_ ev_io *w, int revents)
                 return;
             }
 
+            if (auth) {
+                ss_onetimeauth(ss_addr_to_send + addr_len, ss_addr_to_send, addr_len);
+                addr_len += ONETIMEAUTH_BYTES;
+            }
+
             int s = send(remote->fd, ss_addr_to_send, addr_len, 0);
             free(ss_addr_to_send);
 
@@ -668,9 +674,9 @@ int main(int argc, char **argv)
     USE_TTY();
 
 #ifdef ANDROID
-    while ((c = getopt(argc, argv, "f:s:p:l:k:t:m:i:c:b:L:a:uUvV")) != -1) {
+    while ((c = getopt(argc, argv, "f:s:p:l:k:t:m:i:c:b:L:a:uUvVA")) != -1) {
 #else
-    while ((c = getopt(argc, argv, "f:s:p:l:k:t:m:i:c:b:L:a:uUv")) != -1) {
+    while ((c = getopt(argc, argv, "f:s:p:l:k:t:m:i:c:b:L:a:uUvA")) != -1) {
 #endif
         switch (c) {
         case 's':
@@ -722,6 +728,10 @@ int main(int argc, char **argv)
         case 'v':
             verbose = 1;
             break;
+        case 'A':
+            auth = 1;
+            LOGI("onetime authentication enabled");
+            break;
 #ifdef ANDROID
         case 'V':
             vpn = 1;
diff --git a/src/utils.c b/src/utils.c
index a78b1891..fd277d2c 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -247,6 +247,9 @@ void usage()
     printf(
         "                                  not available in local mode\n");
     printf("\n");
+    printf(
+        "       [-A]                       enable onetime authentication\n");
+    printf("\n");
     printf(
         "       [-L <addr>:<port>]         specify destination server address and port\n");
     printf(