diff --git a/application/config/routes.php b/application/config/routes.php
index 25a1923bc..bcd56732f 100644
--- a/application/config/routes.php
+++ b/application/config/routes.php
@@ -68,7 +68,7 @@ $route['Cis/OtherLvPlan/.*'] = 'Cis/OtherLvPlan/index/$1';
 //Route for LV Plan Stg/Semester/Verband/Gruppe
 $route['Cis/StgOrgLvPlan/.*'] = 'Cis/StgOrgLvPlan/index/$1';
 
-$route['Cis/CoodleExternal/.*'] = 'Cis/CoodleExternal/index/$1';
+$route['Cis/CoodleExternal/(:any)/(:any)'] = 'Cis/CoodleExternal/index/$1/$2';
 
 $route['CoodleFreeBusy/(:any)'] = 'api/frontend/v1/coodle/FreeBusy/getCoodleFreeBusy/$1';
 $route['CoodleIcal/encrypted/(:any)'] = 'api/frontend/v1/coodle/CoodleSurvey/getCoodleIcalEncrypted/$1';
diff --git a/application/controllers/api/frontend/v1/coodle/CoodleSurvey.php b/application/controllers/api/frontend/v1/coodle/CoodleSurvey.php
index f29f24422..3eb531262 100644
--- a/application/controllers/api/frontend/v1/coodle/CoodleSurvey.php
+++ b/application/controllers/api/frontend/v1/coodle/CoodleSurvey.php
@@ -60,7 +60,7 @@ class CoodleSurvey extends FHCAPI_Controller
 		$this->load->helper('hlp_sancho_helper');
 
 		$this->coodlePageUrl = APP_ROOT . "cis.php/Cis/Coodle";
-		$this->coodlePageExternalUrl = APP_ROOT . "cis.php/Cis/CoodleExternal/{key}";
+		$this->coodlePageExternalUrl = APP_ROOT . "cis.php/Cis/CoodleExternal/{surveyId}/{accessKey}";
 		$this->coodleIcalUrl = APP_ROOT . "cis.php/CoodleIcal/{uid}";
 		$this->coodleIcalUrlWithEncryptedUid = APP_ROOT . "cis.php/CoodleIcal/encrypted/{encryptedUid}";
 
@@ -119,13 +119,14 @@ class CoodleSurvey extends FHCAPI_Controller
 
 	public function getSurveyForExternalParticipant()
 	{
-		$key = $this->input->post("key");
-		$validatedKey = $this->validateEncryptedExternalParticipantKey($this->safeDecode($key));
-		if (!$validatedKey)
+		$surveyId = $this->input->post("surveyId");
+		$accessKey = $this->input->post("accessKey");
+		$validatedAccessKey = $this->validateExternalParticipantAccessKey($surveyId, $accessKey);
+		if (!$validatedAccessKey)
 			$this->terminateWithError($this->p->t("coodle", "invalid_access_key_error"));
 
-		$survey = $validatedKey["survey"];
-		$externalParticipant = $validatedKey["externalParticipant"];
+		$survey = $validatedAccessKey["survey"];
+		$externalParticipant = $validatedAccessKey["externalParticipant"];
 
 		$timeslots = $this->CoodleSurveyTimeslotModel->getTimeslots($survey->id);
 		$survey->timeslots = $timeslots;
@@ -234,10 +235,8 @@ class CoodleSurvey extends FHCAPI_Controller
 				);
 			}
 
-			$externalParticipants = $this->CoodleSurveyExternalParticipantModel->getExternalParticipants($surveyId);
+			$externalParticipants = $this->CoodleSurveyExternalParticipantModel->getExternalParticipants($surveyId, true);
 			foreach ($externalParticipants as $externalParticipant) {
-				$encryptedAccessKey = $this->safeEncode($this->getEncryptedExternalParticipantKey($externalParticipant));
-
 				sendSanchoMail(
 					"Sancho_Mail_Coodle_Created_Ext",
 					[
@@ -245,7 +244,7 @@ class CoodleSurvey extends FHCAPI_Controller
 						"surveyCreatorName" => $authUserFullName,
 						"org" => CAMPUS_NAME,
 						"surveyTitle" => $survey->title,
-						"surveyHref" => str_replace("{key}", $encryptedAccessKey, $this->coodlePageExternalUrl),
+						"surveyHref" => $this->getUrlForExternalParticipant($externalParticipant),
 					],
 					$externalParticipant->email,
 					"Coodle Umfrage erstellt / Coodle survey created"
@@ -313,10 +312,8 @@ class CoodleSurvey extends FHCAPI_Controller
 				);
 			}
 
-			$externalParticipants = $this->CoodleSurveyExternalParticipantModel->getExternalParticipants($surveyId);
+			$externalParticipants = $this->CoodleSurveyExternalParticipantModel->getExternalParticipants($surveyId, true);
 			foreach ($externalParticipants as $externalParticipant) {
-				$encryptedAccessKey = $this->safeEncode($this->getEncryptedExternalParticipantKey($externalParticipant));
-
 				sendSanchoMail(
 					"Sancho_Mail_Coodle_Updated_Ext",
 					[
@@ -324,7 +321,7 @@ class CoodleSurvey extends FHCAPI_Controller
 						"surveyCreatorName" => $authUserFullName,
 						"org" => CAMPUS_NAME,
 						"surveyTitle" => $survey->title,
-						"surveyHref" => str_replace("{key}", $encryptedAccessKey, $this->coodlePageExternalUrl),
+						"surveyHref" => $this->getUrlForExternalParticipant($externalParticipant),
 					],
 					$externalParticipant->email,
 					"Coodle Umfrage modifiziert / Coodle survey modified"
@@ -401,16 +398,16 @@ class CoodleSurvey extends FHCAPI_Controller
 
 	public function submitExternalParticipantSelection()
 	{
-		$key = $this->input->post("key");
+		$surveyId = $this->input->post("surveyId");
+		$accessKey = $this->input->post("accessKey");
 		$selection = $this->input->post("selection");
 
-		$key = $this->input->post("key");
-		$validatedKey = $this->validateEncryptedExternalParticipantKey($this->safeDecode($key));
-		if (!$validatedKey)
+		$validatedAccessKey = $this->validateExternalParticipantAccessKey($surveyId, $accessKey);
+		if (!$validatedAccessKey)
 			$this->terminateWithError($this->p->t("coodle", "invalid_access_key_error"));
 
-		$survey = $validatedKey["survey"];
-		$externalParticipant = $validatedKey["externalParticipant"];
+		$survey = $validatedAccessKey["survey"];
+		$externalParticipant = $validatedAccessKey["externalParticipant"];
 
 		if ($survey->completed_at || $survey->canceled_at) {
 			$this->terminateWithError("You can no longer vote in this survey!");
@@ -459,7 +456,7 @@ class CoodleSurvey extends FHCAPI_Controller
 		if ($shouldInformParticipants) {
 			$survey = $this->CoodleSurveyModel->getSurvey($surveyId);
 			$participants = $this->CoodleSurveyParticipantModel->getParticipants($surveyId);
-			$externalParticipants = $this->CoodleSurveyExternalParticipantModel->getExternalParticipants($surveyId);
+			$externalParticipants = $this->CoodleSurveyExternalParticipantModel->getExternalParticipants($surveyId, true);
 			$authUserFullName = getData($this->PersonModel->getFullName(getAuthUID()));
 
 			foreach ($participants as $participant) {
@@ -477,8 +474,6 @@ class CoodleSurvey extends FHCAPI_Controller
 			}
 
 			foreach ($externalParticipants as $externalParticipant) {
-				$encryptedAccessKey = $this->safeEncode($this->getEncryptedExternalParticipantKey($externalParticipant));
-
 				sendSanchoMail(
 					"Sancho_Mail_Coodle_Canceled_Ext",
 					[
@@ -486,7 +481,7 @@ class CoodleSurvey extends FHCAPI_Controller
 						"surveyCreatorName" => $authUserFullName,
 						"org" => CAMPUS_NAME,
 						"surveyTitle" => $survey->title,
-						"surveyHref" => str_replace("{key}", $encryptedAccessKey, $this->coodlePageExternalUrl),
+						"surveyHref" => $this->getUrlForExternalParticipant($externalParticipant),
 					],
 					$externalParticipant->email,
 					'Coodle Umfrage storniert / Coodle survey canceled'
@@ -544,7 +539,7 @@ class CoodleSurvey extends FHCAPI_Controller
 		if ($shouldInformParticipants) {
 			$survey = $this->CoodleSurveyModel->getSurvey($surveyId);
 			$participants = $this->CoodleSurveyParticipantModel->getParticipants($surveyId);
-			$externalParticipants = $this->CoodleSurveyExternalParticipantModel->getExternalParticipants($surveyId);
+			$externalParticipants = $this->CoodleSurveyExternalParticipantModel->getExternalParticipants($surveyId, true);
 			$authUserFullName = getData($this->PersonModel->getFullName(getAuthUID()));
 
 			if ($selectedTimeslot) {
@@ -597,8 +592,6 @@ class CoodleSurvey extends FHCAPI_Controller
 				}
 
 				foreach ($externalParticipants as $externalParticipant) {
-					$encryptedAccessKey = $this->safeEncode($this->getEncryptedExternalParticipantKey($externalParticipant));
-
 					sendSanchoMail(
 						"Sancho_Mail_Coodle_Completed_Ext",
 						[
@@ -607,7 +600,7 @@ class CoodleSurvey extends FHCAPI_Controller
 							"org" => CAMPUS_NAME,
 							"surveyTitle" => $survey->title,
 							"selectedSurveyTimeslot" => $formattedTimeslot,
-							"surveyHref" => str_replace("{key}", $encryptedAccessKey, $this->coodlePageExternalUrl),
+							"surveyHref" => $this->getUrlForExternalParticipant($externalParticipant),
 						],
 						$externalParticipant->email,
 						"Coodle Umfrage vollendet / Coodle survey completed",
@@ -642,8 +635,6 @@ class CoodleSurvey extends FHCAPI_Controller
 				}
 
 				foreach ($externalParticipants as $externalParticipant) {
-					$encryptedAccessKey = $this->safeEncode($this->getEncryptedExternalParticipantKey($externalParticipant));
-
 					sendSanchoMail(
 						"Sancho_Mail_Coodle_Cmpltd_No_Ext",
 						[
@@ -651,7 +642,7 @@ class CoodleSurvey extends FHCAPI_Controller
 							"surveyParticipantName" => $externalParticipant->name,
 							"org" => CAMPUS_NAME,
 							"surveyTitle" => $survey->title,
-							"surveyHref" => str_replace("{key}", $encryptedAccessKey, $this->coodlePageExternalUrl),
+							"surveyHref" => $this->getUrlForExternalParticipant($externalParticipant),
 						],
 						$externalParticipant->email,
 						"Coodle Umfrage vollendet / Coodle survey completed"
@@ -682,7 +673,7 @@ class CoodleSurvey extends FHCAPI_Controller
 			}
 		);
 
-		$externalParticipants = $this->CoodleSurveyExternalParticipantModel->getExternalParticipants($surveyId);
+		$externalParticipants = $this->CoodleSurveyExternalParticipantModel->getExternalParticipants($surveyId, true);
 		$externalParticipantsWithoutVote = array_filter(
 			$externalParticipants,
 			function ($externalParticipant) {
@@ -711,8 +702,6 @@ class CoodleSurvey extends FHCAPI_Controller
 		}
 
 		foreach ($externalParticipantsWithoutVote as $externalParticipant) {
-			$encryptedAccessKey = $this->safeEncode($this->getEncryptedExternalParticipantKey($externalParticipant));
-
 			sendSanchoMail(
 				"Sancho_Mail_Coodle_Reminder_Ext",
 				[
@@ -720,7 +709,7 @@ class CoodleSurvey extends FHCAPI_Controller
 					"surveyParticipantName" => $externalParticipant->name,
 					"org" => CAMPUS_NAME,
 					"surveyTitle" => $survey->title,
-					"surveyHref" => str_replace("{key}", $encryptedAccessKey, $this->coodlePageExternalUrl),
+					"surveyHref" => $this->getUrlForExternalParticipant($externalParticipant),
 				],
 				$externalParticipant->email,
 				"Coodle Umfrage Erinnerung / Coodle survey reminder"
@@ -1023,26 +1012,24 @@ class CoodleSurvey extends FHCAPI_Controller
 		return $decodedValue;
 	}
 
-	private function getEncryptedExternalParticipantKey($externalParticipant)
+	private function getUrlForExternalParticipant($externalParticipant)
 	{
-		$value = "coodleExt_" . $externalParticipant->survey_id . "_" . $externalParticipant->id;
-		return $this->cryptlib->RIJNDAEL_256_ECB(str_pad($value, 32, chr(0)), LVPLAN_CYPHER_KEY, true);
+		return str_replace(
+			["{surveyId}", "{accessKey}"],
+			[$externalParticipant->survey_id, $externalParticipant->access_key],
+			$this->coodlePageExternalUrl
+		);
 	}
 
-	private function validateEncryptedExternalParticipantKey($encryptedKey)
+	private function validateExternalParticipantAccessKey($surveyId, $accessKey)
 	{
-		$decryptedKey = trim($this->cryptlib->RIJNDAEL_256_ECB_DECRYPT($encryptedKey, LVPLAN_CYPHER_KEY, true));
-		$values = explode("_", $decryptedKey);
-		if (count($values) !== 3 || $values[0] !== "coodleExt")
+		if (!$surveyId || !$accessKey)
 			return null;
 
-		$surveyId = $values[1];
-		$externalParticipantId = $values[2];
-
 		$survey = $this->CoodleSurveyModel->getSurvey($surveyId);
-		$externalParticipant = $this->CoodleSurveyExternalParticipantModel->getExternalParticipant($externalParticipantId);
+		$externalParticipant = $this->CoodleSurveyExternalParticipantModel->getExternalParticipantByAccessKey($surveyId, $accessKey);
 
-		if (!$survey || !$externalParticipant || $survey->id !== $externalParticipant->survey_id)
+		if (!$survey || !$externalParticipant)
 			return null;
 
 		return [
diff --git a/application/models/ressource/CoodleSurveyExternalParticipant_model.php b/application/models/ressource/CoodleSurveyExternalParticipant_model.php
index d3ee005ba..cd6ba9906 100644
--- a/application/models/ressource/CoodleSurveyExternalParticipant_model.php
+++ b/application/models/ressource/CoodleSurveyExternalParticipant_model.php
@@ -16,17 +16,19 @@ class CoodleSurveyExternalParticipant_model extends DB_Model
 		$this->_ci =& get_instance();
 	}
 
-	public function getExternalParticipants($surveyId)
+	public function getExternalParticipants($surveyId, $includeAccessKeys = false)
 	{
-		$query = "SELECT *
+		$selectedColumns = $includeAccessKeys ? "*" : "id, survey_id, name, email, selection";
+		$query = "SELECT $selectedColumns
 				FROM $this->dbTable
 				WHERE survey_id = $surveyId
 		";
 		return $this->execQuery($query)->retval;
 	}
 
-	public function getExternalParticipant($externalParticipantId)
+	public function getExternalParticipant($externalParticipantId, $includeAccessKey = false)
 	{
+		$selectedColumns = $includeAccessKey ? "*" : "id, survey_id, name, email, selection";
 		$query = "SELECT *
 			FROM $this->dbTable
 			WHERE id = $externalParticipantId
@@ -35,6 +37,16 @@ class CoodleSurveyExternalParticipant_model extends DB_Model
 		return $this->execQuery($query)->retval[0];
 	}
 
+	public function getExternalParticipantByAccessKey($surveyId, $accessKey)
+	{
+		$query = "SELECT *
+			FROM $this->dbTable
+			WHERE survey_id = $surveyId AND access_key = '$accessKey'
+			LIMIT 1
+		";
+		return $this->execQuery($query)->retval[0];
+	}
+
 	public function updateExternalParticipants($surveyId, $externalParticipants, $timeslots)
 	{
 		$oldExternalParticipants = $this->getExternalParticipants($surveyId);
@@ -82,12 +94,13 @@ class CoodleSurveyExternalParticipant_model extends DB_Model
 				function ($newExternalParticipant) use ($surveyId) {
 					$name = $newExternalParticipant["name"];
 					$email = $newExternalParticipant["email"];
-					return "($surveyId, '$name', '$email', NULL)";
+					$accessKey = uniqid();
+					return "($surveyId, '$name', '$email', '$accessKey', NULL)";
 				},
 				$newExternalParticipants
 			);
 			$insertValues = implode(", ", $insertValues);
-			$insertQuery = "INSERT INTO $this->dbTable (survey_id, name, email, selection) VALUES $insertValues";
+			$insertQuery = "INSERT INTO $this->dbTable (survey_id, name, email, access_key, selection) VALUES $insertValues";
 			$this->execQuery($insertQuery);
 		}
 
diff --git a/public/js/api/factory/coodle.js b/public/js/api/factory/coodle.js
index ec5fa683f..940cdfd75 100644
--- a/public/js/api/factory/coodle.js
+++ b/public/js/api/factory/coodle.js
@@ -55,12 +55,13 @@ export default {
 			},
 		};
 	},
-	getSurveyForExternalParticipant(key) {
+	getSurveyForExternalParticipant(surveyId, accessKey) {
 		return {
 			method: "post",
 			url: "/api/frontend/v1/coodle/CoodleSurvey/getSurveyForExternalParticipant",
 			params: {
-				key,
+				surveyId,
+				accessKey,
 			},
 		};
 	},
@@ -86,12 +87,13 @@ export default {
 			},
 		};
 	},
-	submitExternalParticipantSelection(key, selection) {
+	submitExternalParticipantSelection(surveyId, accessKey, selection) {
 		return {
 			method: "post",
 			url: "/api/frontend/v1/coodle/CoodleSurvey/submitExternalParticipantSelection",
 			params: {
-				key,
+				surveyId,
+				accessKey,
 				selection,
 			},
 		};
diff --git a/public/js/apps/Cis/Cis.js b/public/js/apps/Cis/Cis.js
index 0a6b55823..f67a9de18 100644
--- a/public/js/apps/Cis/Cis.js
+++ b/public/js/apps/Cis/Cis.js
@@ -228,7 +228,7 @@ const router = VueRouter.createRouter({
 			props: true
 		},
 		{
-			path: `/Cis/CoodleExternal/:key`,
+			path: `/Cis/CoodleExternal/:surveyId/:accessKey`,
 			name: 'CoodleExternal',
 			component: CoodleExternal,
 			props: true
diff --git a/public/js/components/Cis/Coodle/Components/CoodleSurvey/CoodleSurveyVotingTable.js b/public/js/components/Cis/Coodle/Components/CoodleSurvey/CoodleSurveyVotingTable.js
index 64ed1db68..b244eec87 100644
--- a/public/js/components/Cis/Coodle/Components/CoodleSurvey/CoodleSurveyVotingTable.js
+++ b/public/js/components/Cis/Coodle/Components/CoodleSurvey/CoodleSurveyVotingTable.js
@@ -263,7 +263,8 @@ export default {
 			if (this.$props.authExternalParticipantId) {
 				selectionSubmissionResponse = await this.$api.call(
 					CoodleApi.submitExternalParticipantSelection(
-						this.$route.params.key,
+						this.$route.params.surveyId,
+						this.$route.params.accessKey,
 						selection,
 					),
 				);
diff --git a/public/js/components/Cis/Coodle/CoodleExternal.js b/public/js/components/Cis/Coodle/CoodleExternal.js
index 7ee2032a6..1bf34f197 100644
--- a/public/js/components/Cis/Coodle/CoodleExternal.js
+++ b/public/js/components/Cis/Coodle/CoodleExternal.js
@@ -15,7 +15,8 @@ export default {
 		async fetchSurvey() {
 			const surveyResponse = await this.$api.call(
 				CoodleApi.getSurveyForExternalParticipant(
-					this.$route.params.key,
+					this.$route.params.surveyId,
+					this.$route.params.accessKey,
 				),
 			);
 
diff --git a/system/dbupdate_3.4/77174_cis4_coodle_tables.php b/system/dbupdate_3.4/77174_cis4_coodle_tables.php
index 11ddd176d..8bae74f8e 100644
--- a/system/dbupdate_3.4/77174_cis4_coodle_tables.php
+++ b/system/dbupdate_3.4/77174_cis4_coodle_tables.php
@@ -102,6 +102,7 @@ if (!$result = @$db->db_query("SELECT 1 FROM campus.tbl_coodle_survey_external_p
 		survey_id int NOT NULL,
 		name varchar(255) NOT NULL,
 		email varchar(255) NOT NULL,
+		access_key varchar(64),
 		selection varchar(255),
 		CONSTRAINT tbl_coodle_surveys_external_participants_id_pk PRIMARY KEY(id),
 		CONSTRAINT tbl_coodle_survey_external_participants_survey_id_fk FOREIGN KEY (survey_id) REFERENCES campus.tbl_coodle_surveys(id)