diff --git a/.gitignore b/.gitignore
index c5cb917..48246a4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,5 @@ conversations/
 .env
 .env.local
 .env.*.local
+# 세션 서명용 자동 생성 시크릿. 절대 커밋 금지.
+.session-secret
diff --git a/src/server/app.ts b/src/server/app.ts
index 014358e..a47b367 100644
--- a/src/server/app.ts
+++ b/src/server/app.ts
@@ -1,10 +1,12 @@
 import express from 'express'
 import session from 'express-session'
 import path from 'node:path'
+import fs from 'node:fs'
 import fsp from 'node:fs/promises'
+import crypto from 'node:crypto'
 import {
   manifestRootPath, manifestDirPath, manifestTermsDirPath,
-  fileDirPath, viewsDirPath, publicDirPath
+  fileDirPath, viewsDirPath, publicDirPath, projectRoot
 } from '../shared/paths.js'
 import {
   ensurePackTermsDir, isPublicTermsFile, listTermsWithLabels, loadPackDefinition
@@ -38,8 +40,28 @@ app.use((_req, res, next) => {
   next()
 })
 
+// 세션 시크릿: 환경변수 우선, 없으면 하드코딩(위조 위험) 대신 영구 랜덤 시크릿을
+// 파일로 생성/보관한다(재시작해도 세션 유지). 파일 접근 불가 시엔 프로세스 수명 동안만
+// 유효한 랜덤값으로 폴백(그래도 하드코딩보다 안전).
+function resolveSessionSecret(): string {
+  const fromEnv = process.env.SESSION_SECRET
+  if (fromEnv && fromEnv.length >= 16) return fromEnv
+  const secretPath = path.join(projectRoot, '.session-secret')
+  try {
+    if (fs.existsSync(secretPath)) {
+      const existing = fs.readFileSync(secretPath, 'utf8').trim()
+      if (existing.length >= 16) return existing
+    }
+    const generated = crypto.randomBytes(32).toString('hex')
+    fs.writeFileSync(secretPath, generated, { mode: 0o600 })
+    return generated
+  } catch {
+    return crypto.randomBytes(32).toString('hex')
+  }
+}
+
 app.use(session({
-  secret: process.env.SESSION_SECRET ?? 'music-quiz-installer-dev-secret',
+  secret: resolveSessionSecret(),
   resave: false,
   saveUninitialized: false,
   cookie: {
diff --git a/src/server/password.ts b/src/server/password.ts
new file mode 100644
index 0000000..e9a5247
--- /dev/null
+++ b/src/server/password.ts
@@ -0,0 +1,48 @@
+import crypto from 'node:crypto'
+
+// 운영자 비밀번호 저장/검증. 외부 의존성 없이 Node 내장 scrypt 사용.
+// 저장 형식: `scrypt$<saltHex>$<hashHex>`. 검증은 항상 상수시간 비교.
+// 기존 account.json 의 평문 비밀번호는 verifyPassword 가 그대로 검증할 수 있고,
+// 로그인 성공 시 호출측에서 hashPassword 로 재저장(자동 업그레이드)한다.
+
+const SCHEME = 'scrypt'
+const KEY_LEN = 32
+const SALT_LEN = 16
+
+export function hashPassword(plain: string): string {
+  const salt = crypto.randomBytes(SALT_LEN)
+  const hash = crypto.scryptSync(plain, salt, KEY_LEN)
+  return `${SCHEME}$${salt.toString('hex')}$${hash.toString('hex')}`
+}
+
+export function isHashed(stored: string): boolean {
+  return typeof stored === 'string' && stored.startsWith(`${SCHEME}$`)
+}
+
+export function verifyPassword(plain: string, stored: string): boolean {
+  if (typeof stored !== 'string' || stored.length === 0) return false
+  if (isHashed(stored)) {
+    const parts = stored.split('$')
+    if (parts.length !== 3) return false
+    let salt: Buffer
+    let expected: Buffer
+    try {
+      salt = Buffer.from(parts[1], 'hex')
+      expected = Buffer.from(parts[2], 'hex')
+    } catch {
+      return false
+    }
+    if (expected.length === 0) return false
+    let derived: Buffer
+    try {
+      derived = crypto.scryptSync(plain, salt, expected.length)
+    } catch {
+      return false
+    }
+    return derived.length === expected.length && crypto.timingSafeEqual(derived, expected)
+  }
+  // 레거시 평문: 길이 노출을 피하려 양쪽을 sha256 으로 고정 길이화한 뒤 상수시간 비교.
+  const a = crypto.createHash('sha256').update(plain, 'utf8').digest()
+  const b = crypto.createHash('sha256').update(stored, 'utf8').digest()
+  return crypto.timingSafeEqual(a, b)
+}
diff --git a/src/server/routes/op.ts b/src/server/routes/op.ts
index 0e9caf3..48b450a 100644
--- a/src/server/routes/op.ts
+++ b/src/server/routes/op.ts
@@ -22,8 +22,10 @@ import {
   saveTerm,
   savePackList,
   setPackPublic,
-  setTermVisibility
+  setTermVisibility,
+  writeAccounts
 } from '../../shared/store.js'
+import { hashPassword, isHashed, verifyPassword } from '../password.js'
 import { fetchReleaseVersions } from '../../shared/mojang.js'
 import { fetchPlaylistEntries, fetchVideoMeta, YtDlpUnavailableError } from '../youtube.js'
 import { requireAuth } from '../middleware/auth.js'
@@ -58,11 +60,20 @@ opRouter.post('/op', async (req, res, next) => {
   try {
     const password = pickFirstValue(req.body.password)
     const accounts = await readAccounts()
-    const matched = accounts.find((entry) => entry.password === password)
+    const matched = accounts.find((entry) => verifyPassword(password, entry.password))
     if (!matched) {
       res.status(401).render('op/login', { error: t('login.wrongPassword') })
       return
     }
+    // 평문으로 저장돼 있던 비밀번호는 로그인 성공 시 scrypt 해시로 자동 업그레이드.
+    if (!isHashed(matched.password)) {
+      try {
+        matched.password = hashPassword(password)
+        await writeAccounts(accounts)
+      } catch {
+        // 업그레이드 실패는 로그인 자체에 영향 주지 않음.
+      }
+    }
     req.session.userId = matched.id
     res.redirect('/op/dashboard')
   } catch (error) {
diff --git a/src/shared/store.ts b/src/shared/store.ts
index 3b76027..a795400 100644
--- a/src/shared/store.ts
+++ b/src/shared/store.ts
@@ -789,3 +789,7 @@ export async function readAccounts(): Promise<AccountEntry[]> {
     throw error
   }
 }
+
+export async function writeAccounts(accounts: AccountEntry[]): Promise<void> {
+  await fsp.writeFile(accountFilePath, `${JSON.stringify(accounts, null, 2)}\n`, 'utf8')
+}