diff --git a/prisma/seed.ts b/prisma/seed.ts
index 7f937d9..53df83e 100644
--- a/prisma/seed.ts
+++ b/prisma/seed.ts
@@ -8,6 +8,7 @@
  *   Phone: 0876677771  |  Email: hongochai10@icloud.com  |  Password: Velik@2026
  */
 
+import * as crypto from 'node:crypto';
 import { PrismaPg } from '@prisma/adapter-pg';
 import {
   PrismaClient,
@@ -64,6 +65,35 @@ const oneYearLater = new Date(now.getTime() + 365 * 24 * 60 * 60 * 1000);
 // Phase 2 — Users & Identity
 // =============================================================================
 
+/**
+ * Compute the same `phoneHash` / `emailHash` that the runtime
+ * `FieldEncryptionService` writes — HMAC-SHA256 over the lowercased,
+ * trimmed value, keyed by HKDF(FIELD_ENCRYPTION_KEY, "goodgo-field-hash").
+ * If neither key is set, returns `null` (matches dev-mode behaviour
+ * where lookups fall back to plaintext `phone` / `email`).
+ */
+function buildFieldHasher(): (value: string | null | undefined) => string | null {
+  const primaryKey =
+    process.env['FIELD_ENCRYPTION_KEY'] ?? process.env['KYC_ENCRYPTION_KEY'];
+  if (!primaryKey) return () => null;
+  const hmacKey = crypto.hkdfSync(
+    'sha256',
+    Buffer.from(primaryKey, 'hex'),
+    Buffer.alloc(0),
+    Buffer.from('goodgo-field-hash', 'utf8'),
+    32,
+  ) as unknown as Buffer;
+  return (value) => {
+    if (!value) return null;
+    return crypto
+      .createHmac('sha256', hmacKey)
+      .update(value.toLowerCase().trim())
+      .digest('hex');
+  };
+}
+
+const computeFieldHash = buildFieldHasher();
+
 async function seedUsers(passwordHash: string) {
   console.log('🔐 Seeding users...');
 
@@ -79,11 +109,24 @@ async function seedUsers(passwordHash: string) {
   ];
 
   for (const u of users) {
+    const phoneHash = computeFieldHash(u.phone);
+    const emailHash = computeFieldHash(u.email);
     await prisma.user.upsert({
       where: { id: u.id },
-      update: { passwordHash, email: u.email, fullName: u.fullName, role: u.role, kycStatus: u.kycStatus },
+      update: {
+        passwordHash,
+        email: u.email,
+        fullName: u.fullName,
+        role: u.role,
+        kycStatus: u.kycStatus,
+        // Keep search-by-phone/email working when re-running seed against
+        // a freshly migrated DB or after a key rotation.
+        phoneHash,
+        emailHash,
+      },
       create: {
         id: u.id, phone: u.phone, email: u.email, passwordHash,
+        phoneHash, emailHash,
         fullName: u.fullName, role: u.role, kycStatus: u.kycStatus,
         avatarUrl: u.avatarUrl, isActive: true, totpEnabled: false, totpBackupCodes: [],
       },
diff --git a/scripts/backfill-user-pii-hashes.ts b/scripts/backfill-user-pii-hashes.ts
new file mode 100644
index 0000000..aafba2c
--- /dev/null
+++ b/scripts/backfill-user-pii-hashes.ts
@@ -0,0 +1,108 @@
+/**
+ * One-shot backfill: compute `phoneHash` + `emailHash` for User rows
+ * that have phone/email but no hash (legacy seed data from before the
+ * privacy hashing layer was introduced). Without hash, the auth flow
+ * `findUnique({ phoneHash })` returns null → "Số điện thoại hoặc mật
+ * khẩu không đúng" even when password is correct.
+ *
+ *   Usage:
+ *     NODE_OPTIONS="-r dotenv/config" DOTENV_CONFIG_PATH=.env \
+ *       FIELD_ENCRYPTION_KEY=<hex-key-matching-cluster-secret> \
+ *       pnpm tsx scripts/backfill-user-pii-hashes.ts [--dry-run]
+ *
+ *   Hash format MUST match `FieldEncryptionService.computeHash`:
+ *     hmacKey = HKDF-SHA256(primaryKey, "", "goodgo-field-hash", 32)
+ *     phoneHash = HMAC-SHA256(hmacKey, value.toLowerCase().trim())
+ */
+import 'dotenv/config';
+import * as crypto from 'node:crypto';
+import { PrismaPg } from '@prisma/adapter-pg';
+import { PrismaClient } from '@prisma/client';
+import pg from 'pg';
+
+const pool = new pg.Pool({ connectionString: process.env['DATABASE_URL'] });
+const adapter = new PrismaPg(pool);
+const prisma = new PrismaClient({ adapter });
+
+const dryRun = process.argv.includes('--dry-run');
+
+const primaryKey =
+  process.env['FIELD_ENCRYPTION_KEY'] ?? process.env['KYC_ENCRYPTION_KEY'];
+if (!primaryKey) {
+  console.error(
+    '✗ FIELD_ENCRYPTION_KEY (or KYC_ENCRYPTION_KEY) must be set so the hash matches the cluster API.',
+  );
+  process.exit(1);
+}
+
+const hmacKey = crypto.hkdfSync(
+  'sha256',
+  Buffer.from(primaryKey, 'hex'),
+  Buffer.alloc(0),
+  Buffer.from('goodgo-field-hash', 'utf8'),
+  32,
+) as unknown as Buffer;
+
+function hash(value: string): string {
+  return crypto
+    .createHmac('sha256', hmacKey)
+    .update(value.toLowerCase().trim())
+    .digest('hex');
+}
+
+async function main(): Promise<void> {
+  // Re-hash ALL users — earlier backfill used plain SHA-256 instead of
+  // HMAC-SHA256, so even rows that already have a hash need to be
+  // recomputed before they match the runtime API's lookup.
+  const users = await prisma.user.findMany({
+    select: { id: true, phone: true, email: true, phoneHash: true, emailHash: true },
+  });
+
+  console.log(`🔍 Found ${users.length} users missing phoneHash or emailHash:`);
+  for (const u of users) {
+    console.log(
+      `   ${u.id}  phone=${u.phone}  email=${u.email ?? '—'}  phoneHash=${
+        u.phoneHash ? 'set' : 'MISSING'
+      }  emailHash=${u.emailHash ? 'set' : 'MISSING'}`,
+    );
+  }
+
+  if (dryRun) {
+    console.log('💡 --dry-run: no writes performed.');
+    return;
+  }
+  if (users.length === 0) {
+    console.log('✓ Nothing to do.');
+    return;
+  }
+
+  let updated = 0;
+  for (const u of users) {
+    const data: { phoneHash?: string; emailHash?: string | null } = {};
+    if (u.phone) {
+      const newPhoneHash = hash(u.phone);
+      if (newPhoneHash !== u.phoneHash) data.phoneHash = newPhoneHash;
+    }
+    if (u.email) {
+      const newEmailHash = hash(u.email);
+      if (newEmailHash !== u.emailHash) data.emailHash = newEmailHash;
+    } else if (u.emailHash) {
+      // user has hash but no email — clear stale hash
+      data.emailHash = null;
+    }
+    if (Object.keys(data).length === 0) continue;
+    await prisma.user.update({ where: { id: u.id }, data });
+    updated += 1;
+  }
+  console.log(`✓ Updated ${updated} users.`);
+}
+
+main()
+  .catch((err) => {
+    console.error(err);
+    process.exitCode = 1;
+  })
+  .finally(async () => {
+    await prisma.$disconnect();
+    await pool.end();
+  });