diff --git a/backend/src/routes/oauth2/authorize.ts b/backend/src/routes/oauth2/authorize.ts
index e05ed80..3316b8b 100644
--- a/backend/src/routes/oauth2/authorize.ts
+++ b/backend/src/routes/oauth2/authorize.ts
@@ -7,6 +7,7 @@ import { ParamError, ScopeError } from '../../errors';
 import type { MyFastifyInstance, StudentsMode } from '../../types';
 
 import {
+  createKey,
   getSessionData, isObject, parseScopeParam, validateOptionalParam, validateParam,
 } from '../../utils';
 
@@ -79,6 +80,7 @@ export default function registerAuthorize(server: MyFastifyInstance): void {
             value: request.query.code_challenge,
           },
           studentsMode,
+          promptSecret: createKey(),
         });
 
         await reply.redirect(urlJoin(websitePrefix, `/authenticate-prompt?prompt_id=${promptId}`));
diff --git a/backend/src/routes/website-api/resolvers/login-resolver.ts b/backend/src/routes/website-api/resolvers/login-resolver.ts
index 8a2b4cc..0cce8ce 100644
--- a/backend/src/routes/website-api/resolvers/login-resolver.ts
+++ b/backend/src/routes/website-api/resolvers/login-resolver.ts
@@ -6,7 +6,7 @@ import {
   Arg, Ctx, Mutation, Resolver,
 } from 'type-graphql';
 import {
-  encryptSymmetrical, encryptWithPublicKey, generatePrivatePublicPair, isObject, requireEnvHex,
+  encryptSymmetrical, encryptWithPublicKey, generatePrivatePublicPair, isObject,
 } from '../../../utils';
 import { InvalidVulcanCredentialsError, UnknownPromptError } from '../errors';
 import LoginResult from '../models/login-result';
@@ -39,7 +39,7 @@ export default class LoginResolver {
     const { privateKey, publicKey } = await generatePrivatePublicPair();
     const encryptedPrivateKey = encryptSymmetrical(
       privateKey,
-      requireEnvHex('CREDENTIALS_PRIVATE_KEY_ENCRYPT_KEY'),
+      prompt.promptSecret,
     );
     const encryptedPassword = encryptWithPublicKey(password, publicKey);
     console.log(diaryList.map((e) => e.serialized.info));
diff --git a/backend/src/types.ts b/backend/src/types.ts
index 753b14f..08da259 100644
--- a/backend/src/types.ts
+++ b/backend/src/types.ts
@@ -24,6 +24,7 @@ export interface Prompt {
     method: 'plain' | 'S256';
   };
   studentsMode: StudentsMode;
+  promptSecret: Buffer;
   loginInfo?: {
     host: string;
     username: string;
diff --git a/backend/src/utils/crypto.ts b/backend/src/utils/crypto.ts
index 3b4d0dd..a9beab3 100644
--- a/backend/src/utils/crypto.ts
+++ b/backend/src/utils/crypto.ts
@@ -18,6 +18,10 @@ export function generatePrivatePublicPair(): Promise<{
   });
 }
 
+export function createKey(): Buffer {
+  return crypto.randomBytes(32);
+}
+
 export function encryptSymmetrical(value: string, key: Buffer): string {
   const ivBuffer = crypto.randomBytes(16);
   const cipher = crypto.createCipheriv('aes-256-cbc', key, ivBuffer);
diff --git a/backend/src/utils/index.ts b/backend/src/utils/index.ts
index 5e8f700..c740007 100644
--- a/backend/src/utils/index.ts
+++ b/backend/src/utils/index.ts
@@ -11,8 +11,8 @@ export function requireEnv(name: string): string {
   return value;
 }
 
-export function requireEnvHex(name: string): Buffer {
-  return Buffer.from(requireEnv(name), 'hex');
+export function requireEnvBase64(name: string): Buffer {
+  return Buffer.from(requireEnv(name), 'base64');
 }
 
 export function parseIntStrict(value: string, radix = 10): number {