diff --git a/examples/companion_radio/MyMesh.cpp b/examples/companion_radio/MyMesh.cpp
index 9de91e45..2dad7866 100644
--- a/examples/companion_radio/MyMesh.cpp
+++ b/examples/companion_radio/MyMesh.cpp
@@ -1294,16 +1294,20 @@ void MyMesh::handleCmdFrame(size_t len) {
 #endif
   } else if (cmd_frame[0] == CMD_IMPORT_PRIVATE_KEY && len >= 65) {
 #if ENABLE_PRIVATE_KEY_IMPORT
-    mesh::LocalIdentity identity;
-    identity.readFrom(&cmd_frame[1], 64);
-    if (_store->saveMainIdentity(identity)) {
-      self_id = identity;
-      writeOKFrame();
-      // re-load contacts, to invalidate ecdh shared_secrets
-      resetContacts();
-      _store->loadContacts(this);
+    if (!mesh::LocalIdentity::validatePrivateKey(&cmd_frame[1])) {
+        writeErrFrame(ERR_CODE_ILLEGAL_ARG); // invalid key
     } else {
-      writeErrFrame(ERR_CODE_FILE_IO_ERROR);
+        mesh::LocalIdentity identity;
+        identity.readFrom(&cmd_frame[1], 64);
+        if (_store->saveMainIdentity(identity)) {
+          self_id = identity;
+          writeOKFrame();
+          // re-load contacts, to invalidate ecdh shared_secrets
+          resetContacts();
+          _store->loadContacts(this);
+        } else {
+          writeErrFrame(ERR_CODE_FILE_IO_ERROR);
+        }
     }
 #else
     writeDisabledFrame();
diff --git a/examples/simple_repeater/MyMesh.cpp b/examples/simple_repeater/MyMesh.cpp
index d926148d..b30072b8 100644
--- a/examples/simple_repeater/MyMesh.cpp
+++ b/examples/simple_repeater/MyMesh.cpp
@@ -744,7 +744,7 @@ void MyMesh::onControlDataRecv(mesh::Packet* packet) {
 MyMesh::MyMesh(mesh::MainBoard &board, mesh::Radio &radio, mesh::MillisecondClock &ms, mesh::RNG &rng,
                mesh::RTCClock &rtc, mesh::MeshTables &tables)
     : mesh::Mesh(radio, ms, rng, rtc, *new StaticPoolPacketManager(32), tables),
-      _cli(board, rtc, sensors, &_prefs, this), telemetry(MAX_PACKET_PAYLOAD - 4), region_map(key_store), temp_map(key_store),
+      _cli(board, rtc, sensors, acl, &_prefs, this), telemetry(MAX_PACKET_PAYLOAD - 4), region_map(key_store), temp_map(key_store),
       discover_limiter(4, 120),  // max 4 every 2 minutes
       anon_limiter(4, 180)   // max 4 every 3 minutes
 #if defined(WITH_RS232_BRIDGE)
@@ -808,7 +808,7 @@ void MyMesh::begin(FILESYSTEM *fs) {
   _fs = fs;
   // load persisted prefs
   _cli.loadPrefs(_fs);
-  acl.load(_fs);
+  acl.load(_fs, self_id);
   // TODO: key_store.begin();
   region_map.load(_fs);
 
@@ -968,7 +968,6 @@ void MyMesh::formatPacketStatsReply(char *reply) {
 }
 
 void MyMesh::saveIdentity(const mesh::LocalIdentity &new_id) {
-  self_id = new_id;
 #if defined(NRF52_PLATFORM) || defined(STM32_PLATFORM)
   IdentityStore store(*_fs, "");
 #elif defined(ESP32)
@@ -978,7 +977,7 @@ void MyMesh::saveIdentity(const mesh::LocalIdentity &new_id) {
 #else
 #error "need to define saveIdentity()"
 #endif
-  store.save("_main", self_id);
+  store.save("_main", new_id);
 }
 
 void MyMesh::clearStats() {
diff --git a/examples/simple_repeater/MyMesh.h b/examples/simple_repeater/MyMesh.h
index f930ee7e..282fc8c2 100644
--- a/examples/simple_repeater/MyMesh.h
+++ b/examples/simple_repeater/MyMesh.h
@@ -86,11 +86,11 @@ class MyMesh : public mesh::Mesh, public CommonCLICallbacks {
   unsigned long next_local_advert, next_flood_advert;
   bool _logging;
   NodePrefs _prefs;
+  ClientACL  acl;
   CommonCLI _cli;
   uint8_t reply_data[MAX_PACKET_PAYLOAD];
   uint8_t reply_path[MAX_PATH_SIZE];
   int8_t  reply_path_len;
-  ClientACL  acl;
   TransportKeyStore key_store;
   RegionMap region_map, temp_map;
   RegionEntry* load_stack[8];
diff --git a/examples/simple_room_server/MyMesh.cpp b/examples/simple_room_server/MyMesh.cpp
index d18a802e..bb62e618 100644
--- a/examples/simple_room_server/MyMesh.cpp
+++ b/examples/simple_room_server/MyMesh.cpp
@@ -587,7 +587,7 @@ void MyMesh::onAckRecv(mesh::Packet *packet, uint32_t ack_crc) {
 MyMesh::MyMesh(mesh::MainBoard &board, mesh::Radio &radio, mesh::MillisecondClock &ms, mesh::RNG &rng,
                mesh::RTCClock &rtc, mesh::MeshTables &tables)
     : mesh::Mesh(radio, ms, rng, rtc, *new StaticPoolPacketManager(32), tables),
-      _cli(board, rtc, sensors, &_prefs, this), telemetry(MAX_PACKET_PAYLOAD - 4) {
+      _cli(board, rtc, sensors, acl, &_prefs, this), telemetry(MAX_PACKET_PAYLOAD - 4) {
   last_millis = 0;
   uptime_millis = 0;
   next_local_advert = next_flood_advert = 0;
@@ -637,7 +637,7 @@ void MyMesh::begin(FILESYSTEM *fs) {
   // load persisted prefs
   _cli.loadPrefs(_fs);
 
-  acl.load(_fs);
+  acl.load(_fs, self_id);
 
   radio_set_params(_prefs.freq, _prefs.bw, _prefs.sf, _prefs.cr);
   radio_set_tx_power(_prefs.tx_power_dbm);
@@ -720,7 +720,6 @@ void MyMesh::setTxPower(uint8_t power_dbm) {
 }
 
 void MyMesh::saveIdentity(const mesh::LocalIdentity &new_id) {
-  self_id = new_id;
 #if defined(NRF52_PLATFORM) || defined(STM32_PLATFORM)
   IdentityStore store(*_fs, "");
 #elif defined(ESP32)
@@ -730,7 +729,7 @@ void MyMesh::saveIdentity(const mesh::LocalIdentity &new_id) {
 #else
 #error "need to define saveIdentity()"
 #endif
-  store.save("_main", self_id);
+  store.save("_main", new_id);
 }
 
 void MyMesh::clearStats() {
diff --git a/examples/simple_room_server/MyMesh.h b/examples/simple_room_server/MyMesh.h
index e7f1fee8..f6adf01e 100644
--- a/examples/simple_room_server/MyMesh.h
+++ b/examples/simple_room_server/MyMesh.h
@@ -94,8 +94,8 @@ class MyMesh : public mesh::Mesh, public CommonCLICallbacks {
   unsigned long next_local_advert, next_flood_advert;
   bool _logging;
   NodePrefs _prefs;
-  CommonCLI _cli;
   ClientACL acl;
+  CommonCLI _cli;
   unsigned long dirty_contacts_expiry;
   uint8_t reply_data[MAX_PACKET_PAYLOAD];
   unsigned long next_push;
diff --git a/examples/simple_sensor/SensorMesh.cpp b/examples/simple_sensor/SensorMesh.cpp
index 4995c55f..201532b9 100644
--- a/examples/simple_sensor/SensorMesh.cpp
+++ b/examples/simple_sensor/SensorMesh.cpp
@@ -695,7 +695,7 @@ void SensorMesh::onAckRecv(mesh::Packet* packet, uint32_t ack_crc) {
 
 SensorMesh::SensorMesh(mesh::MainBoard& board, mesh::Radio& radio, mesh::MillisecondClock& ms, mesh::RNG& rng, mesh::RTCClock& rtc, mesh::MeshTables& tables)
      : mesh::Mesh(radio, ms, rng, rtc, *new StaticPoolPacketManager(32), tables),
-      _cli(board, rtc, sensors, &_prefs, this), telemetry(MAX_PACKET_PAYLOAD - 4)
+      _cli(board, rtc, sensors, acl, &_prefs, this), telemetry(MAX_PACKET_PAYLOAD - 4)
 {
   next_local_advert = next_flood_advert = 0;
   dirty_contacts_expiry = 0;
@@ -736,7 +736,7 @@ void SensorMesh::begin(FILESYSTEM* fs) {
   // load persisted prefs
   _cli.loadPrefs(_fs);
 
-  acl.load(_fs);
+  acl.load(_fs, self_id);
 
   radio_set_params(_prefs.freq, _prefs.bw, _prefs.sf, _prefs.cr);
   radio_set_tx_power(_prefs.tx_power_dbm);
@@ -765,7 +765,6 @@ bool SensorMesh::formatFileSystem() {
 }
 
 void SensorMesh::saveIdentity(const mesh::LocalIdentity& new_id) {
-  self_id = new_id;
 #if defined(NRF52_PLATFORM) || defined(STM32_PLATFORM)
   IdentityStore store(*_fs, "");
 #elif defined(ESP32)
@@ -775,7 +774,7 @@ void SensorMesh::saveIdentity(const mesh::LocalIdentity& new_id) {
 #else
   #error "need to define saveIdentity()"
 #endif
-  store.save("_main", self_id);
+  store.save("_main", new_id);
 }
 
 void SensorMesh::applyTempRadioParams(float freq, float bw, uint8_t sf, uint8_t cr, int timeout_mins) {
diff --git a/examples/simple_sensor/SensorMesh.h b/examples/simple_sensor/SensorMesh.h
index c320eb44..6046a1df 100644
--- a/examples/simple_sensor/SensorMesh.h
+++ b/examples/simple_sensor/SensorMesh.h
@@ -133,9 +133,9 @@ private:
   FILESYSTEM* _fs;
   unsigned long next_local_advert, next_flood_advert;
   NodePrefs _prefs;
+  ClientACL  acl;
   CommonCLI _cli;
   uint8_t reply_data[MAX_PACKET_PAYLOAD];
-  ClientACL  acl;
   unsigned long dirty_contacts_expiry;
   CayenneLPP telemetry;
   uint32_t last_read_time;
diff --git a/src/Identity.cpp b/src/Identity.cpp
index 83298928..ea546274 100644
--- a/src/Identity.cpp
+++ b/src/Identity.cpp
@@ -48,6 +48,50 @@ LocalIdentity::LocalIdentity(RNG* rng) {
   ed25519_create_keypair(pub_key, prv_key, seed);
 }
 
+bool LocalIdentity::validatePrivateKey(const uint8_t prv[64]) {
+    uint8_t pub[32];
+    ed25519_derive_pub(pub, prv); // derive public key from given private key
+
+    // disallow 00 or FF prefixed public keys
+    if (pub[0] == 0x00 || pub[0] == 0xFF) return false;
+
+    // known good test client keypair
+    const uint8_t test_client_prv[64] = {
+      0x70, 0x65, 0xe1, 0x8f, 0xd9, 0xfa, 0xbb, 0x70,
+      0xc1, 0xed, 0x90, 0xdc, 0xa1, 0x99, 0x07, 0xde,
+      0x69, 0x8c, 0x88, 0xb7, 0x09, 0xea, 0x14, 0x6e,
+      0xaf, 0xd9, 0x3d, 0x9b, 0x83, 0x0c, 0x7b, 0x60,
+      0xc4, 0x68, 0x11, 0x93, 0xc7, 0x9b, 0xbc, 0x39,
+      0x94, 0x5b, 0xa8, 0x06, 0x41, 0x04, 0xbb, 0x61,
+      0x8f, 0x8f, 0xd7, 0xa8, 0x4a, 0x0a, 0xf6, 0xf5,
+      0x70, 0x33, 0xd6, 0xe8, 0xdd, 0xcd, 0x64, 0x71
+    };
+    const uint8_t test_client_pub[32] = {
+      0x1e, 0xc7, 0x71, 0x75, 0xb0, 0x91, 0x8e, 0xd2,
+      0x06, 0xf9, 0xae, 0x04, 0xec, 0x13, 0x6d, 0x6d,
+      0x5d, 0x43, 0x15, 0xbb, 0x26, 0x30, 0x54, 0x27,
+      0xf6, 0x45, 0xb4, 0x92, 0xe9, 0x35, 0x0c, 0x10
+    };
+
+    uint8_t ss1[32], ss2[32];
+
+    // shared secret we calculte from test client pubkey and given private key
+    ed25519_key_exchange(ss1, test_client_pub, prv);
+
+    // shared secret they calculate from our derived public key and test client private key
+    ed25519_key_exchange(ss2, pub, test_client_prv);
+
+    // check that both shared secrets match
+    if (memcmp(ss1, ss2, 32) != 0) return false;
+
+    // reject all-zero shared secret
+    for (int i = 0; i < 32; i++) {
+        if (ss1[i] != 0) return true;
+    }
+
+    return false;
+}
+
 bool LocalIdentity::readFrom(Stream& s) {
   bool success = (s.readBytes(pub_key, PUB_KEY_SIZE) == PUB_KEY_SIZE);
   success = success && (s.readBytes(prv_key, PRV_KEY_SIZE) == PRV_KEY_SIZE);
diff --git a/src/Identity.h b/src/Identity.h
index 60e8783b..c3ffcd75 100644
--- a/src/Identity.h
+++ b/src/Identity.h
@@ -76,6 +76,13 @@ public:
   */
   void calcSharedSecret(uint8_t* secret, const uint8_t* other_pub_key) const;
 
+  /**
+   * \brief  Validates that a given private key can be used for ECDH / shared-secret operations.
+   * \param  prv IN - the private key to validate (must be PRV_KEY_SIZE bytes)
+   * \returns true, if the private key is valid for login.
+  */
+  static bool validatePrivateKey(const uint8_t prv[64]);
+
   bool readFrom(Stream& s);
   bool writeTo(Stream& s) const;
   void printTo(Stream& s) const;
diff --git a/src/helpers/ClientACL.cpp b/src/helpers/ClientACL.cpp
index 4ea19fd2..55b70ca5 100644
--- a/src/helpers/ClientACL.cpp
+++ b/src/helpers/ClientACL.cpp
@@ -11,7 +11,8 @@ static File openWrite(FILESYSTEM* _fs, const char* filename) {
   #endif
 }
 
-void ClientACL::load(FILESYSTEM* _fs) {
+void ClientACL::load(FILESYSTEM* fs, const mesh::LocalIdentity& self_id) {
+  _fs = fs;
   num_clients = 0;
   if (_fs->exists("/s_contacts")) {
   #if defined(RP2040_PLATFORM)
@@ -34,11 +35,12 @@ void ClientACL::load(FILESYSTEM* _fs) {
         success = success && (file.read(unused, 2) == 2);
         success = success && (file.read((uint8_t *)&c.out_path_len, 1) == 1);
         success = success && (file.read(c.out_path, 64) == 64);
-        success = success && (file.read(c.shared_secret, PUB_KEY_SIZE) == PUB_KEY_SIZE);
+        success = success && (file.read(c.shared_secret, PUB_KEY_SIZE) == PUB_KEY_SIZE); // will be recalculated below
 
         if (!success) break; // EOF
 
         c.id = mesh::Identity(pub_key);
+        self_id.calcSharedSecret(c.shared_secret, pub_key);  // recalculate shared secrets in case our private key changed
         if (num_clients < MAX_CLIENTS) {
           clients[num_clients++] = c;
         } else {
@@ -50,7 +52,8 @@ void ClientACL::load(FILESYSTEM* _fs) {
   }
 }
 
-void ClientACL::save(FILESYSTEM* _fs, bool (*filter)(ClientInfo*)) {
+void ClientACL::save(FILESYSTEM* fs, bool (*filter)(ClientInfo*)) {
+  _fs = fs;
   File file = openWrite(_fs, "/s_contacts");
   if (file) {
     uint8_t unused[2];
@@ -74,6 +77,16 @@ void ClientACL::save(FILESYSTEM* _fs, bool (*filter)(ClientInfo*)) {
   }
 }
 
+bool ClientACL::clear() {
+  if (!_fs) return false; // no filesystem, nothing to clear
+  if (_fs->exists("/s_contacts")) {
+    _fs->remove("/s_contacts");
+  }
+  memset(clients, 0, sizeof(clients));
+  num_clients = 0;
+  return true;
+}
+
 ClientInfo* ClientACL::getClient(const uint8_t* pubkey, int key_len) {
   for (int i = 0; i < num_clients; i++) {
     if (memcmp(pubkey, clients[i].id.pub_key, key_len) == 0) return &clients[i];  // already known
diff --git a/src/helpers/ClientACL.h b/src/helpers/ClientACL.h
index 1b650edd..dfbc3fce 100644
--- a/src/helpers/ClientACL.h
+++ b/src/helpers/ClientACL.h
@@ -36,6 +36,7 @@ struct ClientInfo {
 #endif
 
 class ClientACL {
+  FILESYSTEM* _fs;
   ClientInfo clients[MAX_CLIENTS];
   int num_clients;
 
@@ -44,8 +45,9 @@ public:
     memset(clients, 0, sizeof(clients));
     num_clients = 0;
   }
-  void load(FILESYSTEM* _fs);
+  void load(FILESYSTEM* _fs, const mesh::LocalIdentity& self_id);
   void save(FILESYSTEM* _fs, bool (*filter)(ClientInfo*)=NULL);
+  bool clear();
 
   ClientInfo* getClient(const uint8_t* pubkey, int key_len);
   ClientInfo* putClient(const mesh::Identity& id, uint8_t init_perms);
diff --git a/src/helpers/CommonCLI.cpp b/src/helpers/CommonCLI.cpp
index 6dac9fff..a8dd9d09 100644
--- a/src/helpers/CommonCLI.cpp
+++ b/src/helpers/CommonCLI.cpp
@@ -443,17 +443,18 @@ void CommonCLI::handleCommand(uint32_t sender_timestamp, const char* command, ch
         StrHelper::strncpy(_prefs->guest_password, &config[15], sizeof(_prefs->guest_password));
         savePrefs();
         strcpy(reply, "OK");
-      } else if (sender_timestamp == 0 &&
-                 memcmp(config, "prv.key ", 8) == 0) { // from serial command line only
+      } else if (memcmp(config, "prv.key ", 8) == 0) {
         uint8_t prv_key[PRV_KEY_SIZE];
         bool success = mesh::Utils::fromHex(prv_key, PRV_KEY_SIZE, &config[8]);
-        if (success) {
+        // only allow rekey if key is valid
+        if (success && mesh::LocalIdentity::validatePrivateKey(prv_key)) {
           mesh::LocalIdentity new_id;
           new_id.readFrom(prv_key, PRV_KEY_SIZE);
           _callbacks->saveIdentity(new_id);
-          strcpy(reply, "OK");
+          strcpy(reply, "OK, reboot to apply! New pubkey: ");
+          mesh::Utils::toHex(&reply[33], new_id.pub_key, PUB_KEY_SIZE);
         } else {
-          strcpy(reply, "Error, invalid key");
+          strcpy(reply, "Error, bad key");
         }
       } else if (memcmp(config, "name ", 5) == 0) {
         if (isValidName(&config[5])) {
diff --git a/src/helpers/CommonCLI.h b/src/helpers/CommonCLI.h
index 3b1d05f9..b0530102 100644
--- a/src/helpers/CommonCLI.h
+++ b/src/helpers/CommonCLI.h
@@ -3,6 +3,7 @@
 #include "Mesh.h"
 #include <helpers/IdentityStore.h>
 #include <helpers/SensorManager.h>
+#include <helpers/ClientACL.h>
 
 #if defined(WITH_RS232_BRIDGE) || defined(WITH_ESPNOW_BRIDGE)
 #define WITH_BRIDGE
@@ -94,6 +95,7 @@ class CommonCLI {
   CommonCLICallbacks* _callbacks;
   mesh::MainBoard* _board;
   SensorManager* _sensors;
+  ClientACL* _acl;
   char tmp[PRV_KEY_SIZE*2 + 4];
 
   mesh::RTCClock* getRTCClock() { return _rtc; }
@@ -101,8 +103,8 @@ class CommonCLI {
   void loadPrefsInt(FILESYSTEM* _fs, const char* filename);
 
 public:
-  CommonCLI(mesh::MainBoard& board, mesh::RTCClock& rtc, SensorManager& sensors, NodePrefs* prefs, CommonCLICallbacks* callbacks)
-      : _board(&board), _rtc(&rtc), _sensors(&sensors), _prefs(prefs), _callbacks(callbacks) { }
+  CommonCLI(mesh::MainBoard& board, mesh::RTCClock& rtc, SensorManager& sensors, ClientACL& acl, NodePrefs* prefs, CommonCLICallbacks* callbacks)
+      : _board(&board), _rtc(&rtc), _sensors(&sensors), _acl(&acl), _prefs(prefs), _callbacks(callbacks) { }
 
   void loadPrefs(FILESYSTEM* _fs);
   void savePrefs(FILESYSTEM* _fs);