diff --git a/.env.development b/.env.development
index 989e7f5e9..9626b3a50 100644
--- a/.env.development
+++ b/.env.development
@@ -64,6 +64,15 @@ S3_SECRET_KEY=minioadmin
 
 MANA_AUTH_PORT=3001
 MANA_AUTH_DATABASE_URL=postgresql://mana:devpassword@localhost:5432/mana_platform
+
+# Encryption Vault Key Encryption Key (KEK)
+# Wraps each user's master key in auth.encryption_vaults. In development
+# this can stay empty (a deterministic dev fallback is used + a loud
+# warning is logged at boot). In production it MUST be set to a base64-
+# encoded 32-byte random value: `openssl rand -base64 32`
+# Future: migrate to KMS / Vault — keep the env var for now.
+MANA_AUTH_KEK=
+
 JWT_ACCESS_TOKEN_EXPIRY=15m
 JWT_REFRESH_TOKEN_EXPIRY=7d
 JWT_ISSUER=mana
diff --git a/services/mana-auth/package.json b/services/mana-auth/package.json
index 44e786a3c..d3621ce96 100644
--- a/services/mana-auth/package.json
+++ b/services/mana-auth/package.json
@@ -6,6 +6,7 @@
 	"scripts": {
 		"dev": "bun run --watch src/index.ts",
 		"start": "bun run src/index.ts",
+		"test": "bun test",
 		"db:push": "drizzle-kit push",
 		"db:generate": "drizzle-kit generate",
 		"db:studio": "drizzle-kit studio"
diff --git a/services/mana-auth/sql/002_encryption_vaults.sql b/services/mana-auth/sql/002_encryption_vaults.sql
new file mode 100644
index 000000000..37c1f14c0
--- /dev/null
+++ b/services/mana-auth/sql/002_encryption_vaults.sql
@@ -0,0 +1,78 @@
+-- Migration: encryption_vaults + encryption_vault_audit
+--
+-- Adds the per-user encryption vault that holds each user's master key
+-- (MK) wrapped with a service-wide Key Encryption Key (KEK). The KEK
+-- itself never lives in the database — it is loaded from the
+-- MANA_AUTH_KEK env var (later: a KMS / Vault).
+--
+-- Run this BEFORE deploying the encryption Phase 2 mana-auth release.
+-- After this migration, run `pnpm db:push` from services/mana-auth/
+-- to materialize the Drizzle-defined columns (or just deploy the new
+-- service — Drizzle creates the tables on boot).
+--
+-- The Drizzle schema definition lives in
+-- src/db/schema/encryption-vaults.ts. This SQL file only adds the
+-- bits Drizzle cannot model: row-level security policies + the FORCE
+-- option that makes the policies apply even to the table owner.
+
+-- ─── Tables ───────────────────────────────────────────────────
+-- Table CREATE statements are intentionally idempotent so this file
+-- can be re-run on a partially-migrated database without crashing.
+
+CREATE TABLE IF NOT EXISTS auth.encryption_vaults (
+    user_id         TEXT PRIMARY KEY REFERENCES auth.users(id) ON DELETE CASCADE,
+    wrapped_mk      TEXT NOT NULL,
+    wrap_iv         TEXT NOT NULL,
+    format_version  SMALLINT NOT NULL DEFAULT 1,
+    kek_id          TEXT NOT NULL DEFAULT 'env-v1',
+    created_at      TIMESTAMPTZ NOT NULL DEFAULT now(),
+    rotated_at      TIMESTAMPTZ
+);
+
+CREATE INDEX IF NOT EXISTS encryption_vaults_user_id_idx
+    ON auth.encryption_vaults (user_id);
+
+CREATE TABLE IF NOT EXISTS auth.encryption_vault_audit (
+    id              TEXT PRIMARY KEY,
+    user_id         TEXT NOT NULL REFERENCES auth.users(id) ON DELETE CASCADE,
+    action          TEXT NOT NULL,
+    ip_address      TEXT,
+    user_agent      TEXT,
+    context         TEXT,
+    status          INTEGER NOT NULL,
+    created_at      TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE INDEX IF NOT EXISTS encryption_vault_audit_user_id_idx
+    ON auth.encryption_vault_audit (user_id);
+
+CREATE INDEX IF NOT EXISTS encryption_vault_audit_created_at_idx
+    ON auth.encryption_vault_audit (created_at);
+
+-- ─── Row Level Security ───────────────────────────────────────
+--
+-- Defense-in-depth: even if a future query forgets the WHERE
+-- user_id = $1 clause, the database itself refuses to leak rows
+-- belonging to other users. The vault service wraps every read
+-- and write in a transaction that calls
+--   set_config('app.current_user_id', userId, true)
+-- before touching the table — RLS rejects anything else.
+--
+-- FORCE makes the policy apply to the table owner too, so the
+-- mana-auth service role cannot bypass it via grants alone.
+
+ALTER TABLE auth.encryption_vaults ENABLE ROW LEVEL SECURITY;
+ALTER TABLE auth.encryption_vaults FORCE ROW LEVEL SECURITY;
+
+DROP POLICY IF EXISTS encryption_vaults_user_isolation ON auth.encryption_vaults;
+CREATE POLICY encryption_vaults_user_isolation ON auth.encryption_vaults
+    USING (user_id = current_setting('app.current_user_id', true))
+    WITH CHECK (user_id = current_setting('app.current_user_id', true));
+
+ALTER TABLE auth.encryption_vault_audit ENABLE ROW LEVEL SECURITY;
+ALTER TABLE auth.encryption_vault_audit FORCE ROW LEVEL SECURITY;
+
+DROP POLICY IF EXISTS encryption_vault_audit_user_isolation ON auth.encryption_vault_audit;
+CREATE POLICY encryption_vault_audit_user_isolation ON auth.encryption_vault_audit
+    USING (user_id = current_setting('app.current_user_id', true))
+    WITH CHECK (user_id = current_setting('app.current_user_id', true));
diff --git a/services/mana-auth/src/config.ts b/services/mana-auth/src/config.ts
index 1619be43b..75b3c9b03 100644
--- a/services/mana-auth/src/config.ts
+++ b/services/mana-auth/src/config.ts
@@ -11,28 +11,51 @@ export interface Config {
 	manaCreditsUrl: string;
 	manaSubscriptionsUrl: string;
 	synapseOidcClientSecret: string;
+	/** Base64-encoded 32-byte AES-256 key encryption key (KEK). Wraps each
+	 *  user's master key in auth.encryption_vaults. Required in production
+	 *  — in development a deterministic dev KEK is auto-generated so the
+	 *  service still boots, with a loud warning. */
+	encryptionKek: string;
 }
 
 export function loadConfig(): Config {
 	const env = (key: string, fallback?: string) => process.env[key] || fallback || '';
+	const nodeEnv = env('NODE_ENV', 'development');
+
+	// Encryption KEK: in production a missing/short value is fatal — the
+	// vault service refuses to mint or unwrap any master keys without a
+	// real KEK. In development we auto-fill with a deterministic dev key
+	// so contributors can run the service without setting up a secret.
+	let encryptionKek = env('MANA_AUTH_KEK');
+	if (!encryptionKek) {
+		if (nodeEnv === 'production') {
+			throw new Error(
+				'mana-auth: MANA_AUTH_KEK env var is required in production. ' +
+					'Set it to a base64-encoded 32-byte random value: ' +
+					'`openssl rand -base64 32`'
+			);
+		}
+		// 32 zero bytes — deterministic, obviously not for production. The
+		// vault service logs a loud warning at startup when it sees this.
+		encryptionKek = 'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=';
+	}
+
 	return {
 		port: parseInt(env('PORT', '3001'), 10),
-		databaseUrl: env(
-			'DATABASE_URL',
-			'postgresql://mana:devpassword@localhost:5432/mana_platform'
-		),
+		databaseUrl: env('DATABASE_URL', 'postgresql://mana:devpassword@localhost:5432/mana_platform'),
 		syncDatabaseUrl: env(
 			'SYNC_DATABASE_URL',
 			'postgresql://mana:devpassword@localhost:5432/mana_sync'
 		),
 		baseUrl: env('BASE_URL', 'http://localhost:3001'),
 		cookieDomain: env('COOKIE_DOMAIN'),
-		nodeEnv: env('NODE_ENV', 'development'),
+		nodeEnv,
 		serviceKey: env('MANA_SERVICE_KEY', 'dev-service-key'),
 		cors: { origins: env('CORS_ORIGINS', 'http://localhost:5173').split(',') },
 		manaNotifyUrl: env('MANA_NOTIFY_URL', 'http://localhost:3013'),
 		manaCreditsUrl: env('MANA_CREDITS_URL', 'http://localhost:3061'),
 		manaSubscriptionsUrl: env('MANA_SUBSCRIPTIONS_URL', 'http://localhost:3063'),
 		synapseOidcClientSecret: env('SYNAPSE_OIDC_CLIENT_SECRET'),
+		encryptionKek,
 	};
 }
diff --git a/services/mana-auth/src/db/schema/encryption-vaults.ts b/services/mana-auth/src/db/schema/encryption-vaults.ts
new file mode 100644
index 000000000..b5bcfd722
--- /dev/null
+++ b/services/mana-auth/src/db/schema/encryption-vaults.ts
@@ -0,0 +1,100 @@
+import { text, timestamp, smallint, integer, index } from 'drizzle-orm/pg-core';
+import { authSchema, users } from './auth';
+
+/**
+ * Per-user encryption vault.
+ *
+ * Holds the user's master key (MK) — wrapped with the service-wide Key
+ * Encryption Key (KEK). The MK itself is never stored in plaintext.
+ * Browsers fetch the unwrapped MK at login via `GET /api/v1/me/encryption-key`
+ * and keep it in sessionStorage for the duration of the session.
+ *
+ * Wire format of the wrapped key:
+ *   AES-GCM-256 over the raw 32-byte MK, with the KEK as key.
+ *   wrapped_mk = AES-GCM-encrypt(MK, KEK, wrap_iv) → ciphertext + 16-byte auth tag.
+ *   The auth tag is appended to wrapped_mk by the Web Crypto / Bun crypto API.
+ *
+ * Why a separate table (and not a column on users)?
+ *   - Lifecycle is independent: a user can rotate their vault without
+ *     touching the user record, and vice versa.
+ *   - Permissions: only the dedicated vault service touches this table,
+ *     so it's easy to grant minimal access via row-level security and
+ *     restrict the audit surface.
+ *   - Future-proofing: when we add per-device sub-keys or recovery wraps,
+ *     they sit naturally next to the master entry.
+ *
+ * RLS is added via raw SQL in the migration file alongside the table.
+ * The migration enables ROW LEVEL SECURITY + FORCE so that even the
+ * mana-auth service role cannot read another user's vault entry without
+ * going through `set_config('app.current_user_id', ...)` first.
+ */
+export const encryptionVaults = authSchema.table(
+	'encryption_vaults',
+	{
+		userId: text('user_id')
+			.primaryKey()
+			.references(() => users.id, { onDelete: 'cascade' }),
+
+		/** AES-GCM ciphertext of the raw 32-byte master key. Includes the
+		 *  16-byte authentication tag at the tail (Web Crypto convention). */
+		wrappedMk: text('wrapped_mk').notNull(),
+
+		/** 12-byte IV used for the wrap operation. Stored base64. */
+		wrapIv: text('wrap_iv').notNull(),
+
+		/** Wire format version. Lets us migrate to a different KDF or AEAD
+		 *  later without rewriting every existing row at once. */
+		formatVersion: smallint('format_version').notNull().default(1),
+
+		/** KEK identifier — currently always 'env-v1' (the env-loaded KEK).
+		 *  Will become a KMS key ARN / Vault path / etc. when we move
+		 *  off the env-var KEK. Stored so a future rotation knows which
+		 *  KEK to unwrap with. */
+		kekId: text('kek_id').notNull().default('env-v1'),
+
+		createdAt: timestamp('created_at', { withTimezone: true }).defaultNow().notNull(),
+		rotatedAt: timestamp('rotated_at', { withTimezone: true }),
+	},
+	(table) => [index('encryption_vaults_user_id_idx').on(table.userId)]
+);
+
+export type EncryptionVault = typeof encryptionVaults.$inferSelect;
+export type NewEncryptionVault = typeof encryptionVaults.$inferInsert;
+
+/**
+ * Append-only audit trail of vault accesses (init, fetch, rotate). Used
+ * for security investigations and compliance reporting. Not exposed to
+ * users — only the admin endpoints can read this.
+ *
+ * Why a separate table instead of dumping into a generic audit log?
+ *   - Encryption vault access is the highest-sensitivity operation in
+ *     the entire system; a dedicated table makes the threat-monitoring
+ *     query trivial ("show me all fetches in the last 24h grouped by
+ *     IP / user-agent").
+ *   - Retention can be tuned independently (longer than ordinary auth
+ *     logs to support late-discovered breaches).
+ */
+export const encryptionVaultAudit = authSchema.table(
+	'encryption_vault_audit',
+	{
+		id: text('id').primaryKey(), // nanoid
+		userId: text('user_id')
+			.references(() => users.id, { onDelete: 'cascade' })
+			.notNull(),
+		action: text('action').notNull(), // 'init' | 'fetch' | 'rotate' | 'failed_fetch'
+		ipAddress: text('ip_address'),
+		userAgent: text('user_agent'),
+		/** Free-form context (e.g. failure reason, format version touched). */
+		context: text('context'),
+		/** HTTP status returned to the client — useful for spotting probing. */
+		status: integer('status').notNull(),
+		createdAt: timestamp('created_at', { withTimezone: true }).defaultNow().notNull(),
+	},
+	(table) => [
+		index('encryption_vault_audit_user_id_idx').on(table.userId),
+		index('encryption_vault_audit_created_at_idx').on(table.createdAt),
+	]
+);
+
+export type EncryptionVaultAudit = typeof encryptionVaultAudit.$inferSelect;
+export type NewEncryptionVaultAudit = typeof encryptionVaultAudit.$inferInsert;
diff --git a/services/mana-auth/src/db/schema/index.ts b/services/mana-auth/src/db/schema/index.ts
index fae636ca4..b2d3ad7b7 100644
--- a/services/mana-auth/src/db/schema/index.ts
+++ b/services/mana-auth/src/db/schema/index.ts
@@ -2,3 +2,4 @@ export * from './auth';
 export * from './organizations';
 export * from './api-keys';
 export * from './login-attempts';
+export * from './encryption-vaults';
diff --git a/services/mana-auth/src/index.ts b/services/mana-auth/src/index.ts
index 737d7dfa3..9d5c6a47d 100644
--- a/services/mana-auth/src/index.ts
+++ b/services/mana-auth/src/index.ts
@@ -17,10 +17,13 @@ import { SecurityEventsService, AccountLockoutService } from './services/securit
 import { SignupLimitService } from './services/signup-limit';
 import { ApiKeysService } from './services/api-keys';
 import { UserDataService } from './services/user-data';
+import { EncryptionVaultService } from './services/encryption-vault';
+import { loadKek } from './services/encryption-vault/kek';
 import { createAuthRoutes } from './routes/auth';
 import { createGuildRoutes } from './routes/guilds';
 import { createApiKeyRoutes, createApiKeyValidationRoute } from './routes/api-keys';
 import { createMeRoutes } from './routes/me';
+import { createEncryptionVaultRoutes } from './routes/encryption-vault';
 import { createSettingsRoutes } from './routes/settings';
 import { createAdminRoutes } from './routes/admin';
 
@@ -30,12 +33,18 @@ const config = loadConfig();
 const db = getDb(config.databaseUrl);
 const auth = createBetterAuth(config.databaseUrl);
 
+// Load the Key Encryption Key before any vault operation can run.
+// Top-level await is supported by Bun. Throws if MANA_AUTH_KEK is
+// missing in production or malformed in any environment.
+await loadKek(config.encryptionKek);
+
 // Initialize services
 const security = new SecurityEventsService(db);
 const lockout = new AccountLockoutService(db);
 const signupLimit = new SignupLimitService(db);
 const apiKeysService = new ApiKeysService(db);
 const userDataService = new UserDataService(db, config);
+const encryptionVaultService = new EncryptionVaultService(db);
 
 // ─── App ────────────────────────────────────────────────────
 
@@ -83,6 +92,11 @@ app.route('/api/v1/api-keys', createApiKeyValidationRoute(apiKeysService));
 app.use('/api/v1/me/*', jwtAuth(config.baseUrl));
 app.route('/api/v1/me', createMeRoutes(userDataService));
 
+// ─── Encryption vault (per-user master key custody) ────────
+// Mounted under /me so it inherits the JWT middleware above and shows
+// up in the same self-service surface as the GDPR endpoints.
+app.route('/api/v1/me/encryption-vault', createEncryptionVaultRoutes(encryptionVaultService));
+
 // ─── Settings ──────────────────────────────────────────────
 
 app.use('/api/v1/settings/*', jwtAuth(config.baseUrl));
diff --git a/services/mana-auth/src/routes/encryption-vault.ts b/services/mana-auth/src/routes/encryption-vault.ts
new file mode 100644
index 000000000..1ed1de4c8
--- /dev/null
+++ b/services/mana-auth/src/routes/encryption-vault.ts
@@ -0,0 +1,119 @@
+/**
+ * Encryption vault routes — `/api/v1/me/encryption-vault/*`
+ *
+ * The browser fetches its master key from these endpoints at login and
+ * stashes the result in sessionStorage. All routes require a valid JWT
+ * via the standard jwt-auth middleware — there is no admin or service-
+ * to-service variant. The vault is a strictly per-user resource.
+ *
+ * Routes:
+ *   POST /init       → Mints a fresh MK if none exists, then returns it.
+ *                      Idempotent — calling twice is safe and returns
+ *                      the existing key on the second call.
+ *   GET  /key        → Returns the existing MK. 404 if not initialised
+ *                      (client should call /init).
+ *   POST /rotate     → Mints a new MK, replaces the existing wrap. Caller
+ *                      MUST handle re-encryption of any data sealed with
+ *                      the old key.
+ *
+ * The master key crosses the wire as base64 — never as raw bytes — so
+ * a JSON-aware client (browser, curl, jq) can deserialise it without
+ * worrying about binary content.
+ *
+ * Audit logging is the service's job; the route just passes ip + UA in
+ * via AuditContext.
+ */
+
+import { Hono, type Context } from 'hono';
+import type { AuthUser } from '../middleware/jwt-auth';
+import {
+	EncryptionVaultService,
+	VaultNotFoundError,
+	type AuditContext,
+} from '../services/encryption-vault';
+
+type AppContext = Context<{ Variables: { user: AuthUser } }>;
+
+export function createEncryptionVaultRoutes(vaultService: EncryptionVaultService) {
+	const app = new Hono<{ Variables: { user: AuthUser } }>();
+
+	// ─── POST /init ──────────────────────────────────────────
+	// Idempotent. First call creates a vault row; subsequent calls
+	// return the existing master key. The client uses this on first
+	// login per device — `init` is also a safe fallback if `/key`
+	// returns 404 because the user has somehow never been initialised.
+	app.post('/init', async (c) => {
+		const user = c.get('user');
+		const ctx = readAuditContext(c);
+
+		const result = await vaultService.init(user.userId, ctx);
+
+		return c.json({
+			masterKey: bytesToBase64(result.masterKey),
+			formatVersion: result.formatVersion,
+			kekId: result.kekId,
+		});
+	});
+
+	// ─── GET /key ────────────────────────────────────────────
+	// The hot path: every Phase 3 client calls this immediately after
+	// login. Returns the unwrapped MK as base64 over HTTPS. The vault
+	// service writes a `fetch` audit row on success, `failed_fetch` on
+	// any error path.
+	app.get('/key', async (c) => {
+		const user = c.get('user');
+		const ctx = readAuditContext(c);
+
+		try {
+			const result = await vaultService.getMasterKey(user.userId, ctx);
+			return c.json({
+				masterKey: bytesToBase64(result.masterKey),
+				formatVersion: result.formatVersion,
+				kekId: result.kekId,
+			});
+		} catch (err) {
+			if (err instanceof VaultNotFoundError) {
+				return c.json({ error: 'vault not initialised', code: 'VAULT_NOT_INITIALISED' }, 404);
+			}
+			throw err; // 500 via global error handler + audit row already written
+		}
+	});
+
+	// ─── POST /rotate ────────────────────────────────────────
+	// Destructive. Mints a fresh MK and overwrites the wrap. The old MK
+	// is gone forever. Routes do NOT enforce a 2FA challenge here —
+	// that's a UX decision the front-end has to enforce before calling.
+	// (Future: add a `requires2fa: true` flag and short-circuit here if
+	// the JWT lacks a recent step-up claim.)
+	app.post('/rotate', async (c) => {
+		const user = c.get('user');
+		const ctx = readAuditContext(c);
+
+		const result = await vaultService.rotate(user.userId, ctx);
+		return c.json({
+			masterKey: bytesToBase64(result.masterKey),
+			formatVersion: result.formatVersion,
+			kekId: result.kekId,
+		});
+	});
+
+	return app;
+}
+
+// ─── Helpers ─────────────────────────────────────────────────
+
+function readAuditContext(c: AppContext): AuditContext {
+	return {
+		ipAddress:
+			c.req.header('x-forwarded-for')?.split(',')[0]?.trim() ||
+			c.req.header('x-real-ip') ||
+			undefined,
+		userAgent: c.req.header('user-agent') || undefined,
+	};
+}
+
+function bytesToBase64(bytes: Uint8Array): string {
+	let bin = '';
+	for (let i = 0; i < bytes.length; i++) bin += String.fromCharCode(bytes[i]);
+	return btoa(bin);
+}
diff --git a/services/mana-auth/src/services/encryption-vault/index.ts b/services/mana-auth/src/services/encryption-vault/index.ts
new file mode 100644
index 000000000..4b55ab63b
--- /dev/null
+++ b/services/mana-auth/src/services/encryption-vault/index.ts
@@ -0,0 +1,249 @@
+/**
+ * EncryptionVaultService — server-side master key custody.
+ *
+ * Responsibilities:
+ *   - init(userId): mint a fresh per-user master key, wrap it with the
+ *     KEK, and store it. Idempotent: returns the existing vault if one
+ *     already exists for this user.
+ *   - getMasterKey(userId): unwrap the stored MK and return the raw 32
+ *     bytes ready for HTTPS transit to the browser.
+ *   - rotate(userId): mint a fresh MK, replace the existing wrap. The
+ *     old MK is GONE — the caller must ensure all encrypted data is
+ *     re-encrypted (or accepted as lost) before invoking rotate.
+ *
+ * All reads and writes go through `withUserScope(userId, fn)` so the
+ * row-level-security policy on `auth.encryption_vaults` and
+ * `auth.encryption_vault_audit` is satisfied. The transaction sets
+ * `app.current_user_id` via `set_config(..., true)` (LOCAL scope) so
+ * even if a future bug forgets the WHERE clause, the database refuses
+ * to expose another user's vault entry.
+ *
+ * The audit table records every action — successful and failed — with
+ * IP, user-agent, and HTTP status. Routes pass these in via the
+ * AuditContext shape.
+ */
+
+import { eq, sql } from 'drizzle-orm';
+import { nanoid } from 'nanoid';
+import type { Database } from '../../db/connection';
+import {
+	encryptionVaults,
+	encryptionVaultAudit,
+	type EncryptionVault,
+} from '../../db/schema/encryption-vaults';
+import { wrapMasterKey, unwrapMasterKey, generateMasterKey, activeKekId } from './kek';
+
+/** Per-request metadata used for audit log entries. */
+export interface AuditContext {
+	ipAddress?: string;
+	userAgent?: string;
+}
+
+export interface VaultFetchResult {
+	/** Raw 32 bytes of the unwrapped master key. Caller must base64-encode
+	 *  before placing in the JSON response body. */
+	masterKey: Uint8Array;
+	/** Format version of the wrap currently in storage — bumps if we ever
+	 *  migrate the wire format. The client doesn't usually care, but the
+	 *  rotate flow uses it to know whether a re-wrap is needed. */
+	formatVersion: number;
+	/** Which KEK produced the wrapped value. */
+	kekId: string;
+}
+
+export class EncryptionVaultService {
+	constructor(private db: Database) {}
+
+	// ─── Public API ──────────────────────────────────────────
+
+	/**
+	 * Idempotent vault initialisation. Returns the existing vault row if
+	 * one already exists for this user, otherwise mints a fresh master
+	 * key, wraps it with the KEK, and inserts.
+	 *
+	 * Returns the unwrapped master key bytes either way so the client
+	 * can stash them immediately after the call.
+	 */
+	async init(userId: string, ctx: AuditContext = {}): Promise<VaultFetchResult> {
+		return this.withUserScope(userId, async (tx) => {
+			const existing = await tx
+				.select()
+				.from(encryptionVaults)
+				.where(eq(encryptionVaults.userId, userId))
+				.limit(1);
+
+			if (existing.length > 0) {
+				// Already initialised — fall through to a regular fetch.
+				const masterKey = await unwrapMasterKey(existing[0].wrappedMk, existing[0].wrapIv);
+				await this.writeAudit(tx, userId, 'init', ctx, 200, 'already-exists');
+				return {
+					masterKey,
+					formatVersion: existing[0].formatVersion,
+					kekId: existing[0].kekId,
+				};
+			}
+
+			const mkBytes = generateMasterKey();
+			const { wrappedMk, wrapIv } = await wrapMasterKey(mkBytes);
+
+			await tx.insert(encryptionVaults).values({
+				userId,
+				wrappedMk,
+				wrapIv,
+				formatVersion: 1,
+				kekId: activeKekId(),
+			});
+
+			await this.writeAudit(tx, userId, 'init', ctx, 201, 'created');
+
+			return { masterKey: mkBytes, formatVersion: 1, kekId: activeKekId() };
+		});
+	}
+
+	/**
+	 * Fetches the current master key for a user. Throws if no vault has
+	 * been initialised yet — the route handler converts that to a 404 so
+	 * the client can call init() to bootstrap.
+	 */
+	async getMasterKey(userId: string, ctx: AuditContext = {}): Promise<VaultFetchResult> {
+		return this.withUserScope(userId, async (tx) => {
+			const rows = await tx
+				.select()
+				.from(encryptionVaults)
+				.where(eq(encryptionVaults.userId, userId))
+				.limit(1);
+
+			if (rows.length === 0) {
+				await this.writeAudit(tx, userId, 'failed_fetch', ctx, 404, 'not-initialised');
+				throw new VaultNotFoundError(userId);
+			}
+
+			const row = rows[0];
+			let masterKey: Uint8Array;
+			try {
+				masterKey = await unwrapMasterKey(row.wrappedMk, row.wrapIv);
+			} catch (err) {
+				// Auth-tag mismatch, wrong KEK, malformed row — all the same
+				// to the caller (500), but we want a clear audit trail.
+				await this.writeAudit(
+					tx,
+					userId,
+					'failed_fetch',
+					ctx,
+					500,
+					`unwrap-failed: ${(err as Error).message}`
+				);
+				throw err;
+			}
+
+			await this.writeAudit(tx, userId, 'fetch', ctx, 200, null);
+			return { masterKey, formatVersion: row.formatVersion, kekId: row.kekId };
+		});
+	}
+
+	/**
+	 * Rotates a user's master key. The old MK is permanently lost — the
+	 * caller is responsible for re-encrypting any data that was sealed
+	 * with it BEFORE calling this method, or accepting the loss.
+	 *
+	 * Use cases:
+	 *   - Suspected device compromise → rotate + force logout all
+	 *     sessions + tell user "your old data needs re-syncing"
+	 *   - Periodic best-practice rotation (rare in this design — the
+	 *     KEK can rotate without touching the MK)
+	 */
+	async rotate(userId: string, ctx: AuditContext = {}): Promise<VaultFetchResult> {
+		return this.withUserScope(userId, async (tx) => {
+			const mkBytes = generateMasterKey();
+			const { wrappedMk, wrapIv } = await wrapMasterKey(mkBytes);
+
+			const updated = await tx
+				.update(encryptionVaults)
+				.set({
+					wrappedMk,
+					wrapIv,
+					kekId: activeKekId(),
+					rotatedAt: new Date(),
+				})
+				.where(eq(encryptionVaults.userId, userId))
+				.returning();
+
+			if (updated.length === 0) {
+				// No existing vault — treat rotate as init.
+				await tx.insert(encryptionVaults).values({
+					userId,
+					wrappedMk,
+					wrapIv,
+					formatVersion: 1,
+					kekId: activeKekId(),
+				});
+				await this.writeAudit(tx, userId, 'rotate', ctx, 201, 'init-on-rotate');
+			} else {
+				await this.writeAudit(tx, userId, 'rotate', ctx, 200, null);
+			}
+
+			return { masterKey: mkBytes, formatVersion: 1, kekId: activeKekId() };
+		});
+	}
+
+	// ─── Internals ───────────────────────────────────────────
+
+	/**
+	 * Wraps `fn` in a transaction with `app.current_user_id` set to the
+	 * given userId via `set_config(..., true)`. RLS policies on
+	 * encryption_vaults and encryption_vault_audit then admit only rows
+	 * matching that userId — defense in depth on top of the explicit
+	 * WHERE clauses.
+	 *
+	 * `set_config(name, value, true)` is the parameterised equivalent of
+	 * `SET LOCAL` (which can't take bind parameters). The `true` flag
+	 * scopes the setting to the current transaction.
+	 */
+	private async withUserScope<T>(
+		userId: string,
+		fn: (tx: Parameters<Parameters<Database['transaction']>[0]>[0]) => Promise<T>
+	): Promise<T> {
+		if (!userId) {
+			throw new Error('mana-auth/vault: userId is required for vault operations');
+		}
+		return this.db.transaction(async (tx) => {
+			await tx.execute(sql`SELECT set_config('app.current_user_id', ${userId}, true)`);
+			return fn(tx);
+		});
+	}
+
+	private async writeAudit(
+		tx: Parameters<Parameters<Database['transaction']>[0]>[0],
+		userId: string,
+		action: 'init' | 'fetch' | 'rotate' | 'failed_fetch',
+		ctx: AuditContext,
+		status: number,
+		context: string | null
+	): Promise<void> {
+		await tx.insert(encryptionVaultAudit).values({
+			id: nanoid(),
+			userId,
+			action,
+			ipAddress: ctx.ipAddress ?? null,
+			userAgent: ctx.userAgent ?? null,
+			context,
+			status,
+		});
+	}
+}
+
+/**
+ * Thrown when a fetch is attempted against a user who hasn't called
+ * init() yet. Routes catch this specifically to convert it to a 404
+ * (so the client can react with init() instead of treating it as a
+ * server error).
+ */
+export class VaultNotFoundError extends Error {
+	constructor(public userId: string) {
+		super(`encryption vault not initialised for user ${userId}`);
+		this.name = 'VaultNotFoundError';
+	}
+}
+
+/** Re-export the type for route handlers. */
+export type { EncryptionVault };
diff --git a/services/mana-auth/src/services/encryption-vault/kek.test.ts b/services/mana-auth/src/services/encryption-vault/kek.test.ts
new file mode 100644
index 000000000..3632f610b
--- /dev/null
+++ b/services/mana-auth/src/services/encryption-vault/kek.test.ts
@@ -0,0 +1,134 @@
+/**
+ * KEK (Key Encryption Key) helper tests.
+ *
+ * Pure crypto — no Postgres or Drizzle dependency. Run with `bun test`.
+ *
+ * The EncryptionVaultService itself is tested via integration tests
+ * against a real Postgres instance because the row-level-security
+ * behaviour cannot be faithfully reproduced with pg-mem or sqlite.
+ * Those integration tests live alongside the existing mana-sync test
+ * pattern (separate test database, set up in CI before the run).
+ */
+
+import { describe, it, expect, beforeEach } from 'bun:test';
+import {
+	loadKek,
+	wrapMasterKey,
+	unwrapMasterKey,
+	generateMasterKey,
+	activeKekId,
+	_resetForTesting,
+} from './kek';
+
+// Deterministic 32-byte test KEK (NOT the dev fallback — that's all
+// zeros, which would trigger the warning every test run).
+const TEST_KEK_BASE64 = 'AQIDBAUGBwgJCgsMDQ4PEBESExQVFhcYGRobHB0eHyA=';
+
+beforeEach(async () => {
+	_resetForTesting();
+	await loadKek(TEST_KEK_BASE64);
+});
+
+describe('loadKek', () => {
+	it('imports a valid 32-byte base64 KEK', () => {
+		expect(activeKekId()).toBe('env-v1');
+	});
+
+	it('rejects a base64 string that decodes to the wrong length', async () => {
+		_resetForTesting();
+		// 16 bytes — half the size of an AES-256 KEK
+		await expect(loadKek('AAAAAAAAAAAAAAAAAAAAAA==')).rejects.toThrow(/expected 32 bytes/);
+	});
+
+	it('is idempotent — second call is a no-op', async () => {
+		// Already loaded in beforeEach. A second call should not throw.
+		await loadKek(TEST_KEK_BASE64);
+		expect(activeKekId()).toBe('env-v1');
+	});
+
+	it('refuses to expose kekId before loadKek is called', () => {
+		_resetForTesting();
+		expect(() => activeKekId()).toThrow(/loadKek\(\) not called/);
+	});
+});
+
+describe('generateMasterKey', () => {
+	it('returns 32 bytes of cryptographic randomness', () => {
+		const a = generateMasterKey();
+		const b = generateMasterKey();
+		expect(a).toBeInstanceOf(Uint8Array);
+		expect(a.length).toBe(32);
+		expect(b.length).toBe(32);
+		// Two consecutive calls should virtually never collide
+		expect(Buffer.from(a).toString('hex')).not.toBe(Buffer.from(b).toString('hex'));
+	});
+});
+
+describe('wrapMasterKey / unwrapMasterKey roundtrip', () => {
+	it('roundtrips a freshly generated master key', async () => {
+		const mk = generateMasterKey();
+		const { wrappedMk, wrapIv } = await wrapMasterKey(mk);
+
+		expect(typeof wrappedMk).toBe('string');
+		expect(typeof wrapIv).toBe('string');
+		expect(wrappedMk.length).toBeGreaterThan(0);
+		expect(wrapIv.length).toBeGreaterThan(0);
+
+		const recovered = await unwrapMasterKey(wrappedMk, wrapIv);
+		expect(Buffer.from(recovered).toString('hex')).toBe(Buffer.from(mk).toString('hex'));
+	});
+
+	it('produces a different ciphertext for the same MK on each call', async () => {
+		const mk = generateMasterKey();
+		const a = await wrapMasterKey(mk);
+		const b = await wrapMasterKey(mk);
+		const c = await wrapMasterKey(mk);
+		expect(a.wrappedMk).not.toBe(b.wrappedMk);
+		expect(b.wrappedMk).not.toBe(c.wrappedMk);
+		expect(a.wrapIv).not.toBe(b.wrapIv);
+		// All three still unwrap correctly
+		expect(Buffer.from(await unwrapMasterKey(a.wrappedMk, a.wrapIv)).toString('hex')).toBe(
+			Buffer.from(mk).toString('hex')
+		);
+		expect(Buffer.from(await unwrapMasterKey(b.wrappedMk, b.wrapIv)).toString('hex')).toBe(
+			Buffer.from(mk).toString('hex')
+		);
+	});
+
+	it('rejects a master key of the wrong length', async () => {
+		await expect(wrapMasterKey(new Uint8Array(16))).rejects.toThrow(/32-byte master key/);
+		await expect(wrapMasterKey(new Uint8Array(64))).rejects.toThrow(/32-byte master key/);
+	});
+});
+
+describe('unwrapMasterKey error paths', () => {
+	it('throws on tampered ciphertext (auth tag mismatch)', async () => {
+		const mk = generateMasterKey();
+		const { wrappedMk, wrapIv } = await wrapMasterKey(mk);
+		// Flip the last base64 character to corrupt the auth tag
+		const lastChar = wrappedMk.charAt(wrappedMk.length - 1);
+		const swapped = lastChar === 'A' ? 'B' : 'A';
+		const tampered = wrappedMk.slice(0, -1) + swapped;
+		await expect(unwrapMasterKey(tampered, wrapIv)).rejects.toThrow();
+	});
+
+	it('throws on a wrong-length IV', async () => {
+		const mk = generateMasterKey();
+		const { wrappedMk } = await wrapMasterKey(mk);
+		const badIv = 'AAAAAAAA'; // 6 bytes after base64 decode
+		await expect(unwrapMasterKey(wrappedMk, badIv)).rejects.toThrow(/12-byte IV/);
+	});
+
+	it('throws when a different KEK was used to wrap', async () => {
+		// Wrap with the test KEK
+		const mk = generateMasterKey();
+		const { wrappedMk, wrapIv } = await wrapMasterKey(mk);
+
+		// Reload with a different KEK
+		_resetForTesting();
+		const otherKek = 'IB8eHRwbGhkYFxYVFBMSERAPDg0MCwoJCAcGBQQDAgE=';
+		await loadKek(otherKek);
+
+		await expect(unwrapMasterKey(wrappedMk, wrapIv)).rejects.toThrow();
+	});
+});
diff --git a/services/mana-auth/src/services/encryption-vault/kek.ts b/services/mana-auth/src/services/encryption-vault/kek.ts
new file mode 100644
index 000000000..7080b94bf
--- /dev/null
+++ b/services/mana-auth/src/services/encryption-vault/kek.ts
@@ -0,0 +1,180 @@
+/**
+ * Key Encryption Key (KEK) loader and AES-GCM wrap/unwrap helpers.
+ *
+ * The KEK is a 32-byte AES-256 key loaded from the MANA_AUTH_KEK env
+ * var (base64). It wraps each user's master key (MK) before storage in
+ * `auth.encryption_vaults.wrapped_mk`. The KEK itself NEVER touches the
+ * database — it lives only in process memory and is sourced from a
+ * single environment variable that must be provisioned out of band
+ * (Docker secret, KMS-injected, etc.).
+ *
+ * Why a separate AES-GCM wrap instead of e.g. libsodium SecretBox?
+ *   - Both Bun and the browser ship native Web Crypto AES-GCM, so the
+ *     wire format is portable across the future "client-side wrap"
+ *     scenario without bundling extra crypto deps.
+ *   - The encryption-vault rows live behind row-level security and
+ *     are never exposed; the threat model here is "what if an
+ *     attacker dumps the auth DB?", which AES-GCM-256 with a 256-bit
+ *     KEK fully addresses.
+ *
+ * Future migration to KMS / Vault:
+ *   The KEK loader is a single function. When we move to AWS KMS or
+ *   Hashicorp Vault, only `loadKek()` changes. The `wrapMasterKey` /
+ *   `unwrapMasterKey` callers stay identical, and the wrapped_mk
+ *   column gets a new `kek_id` value to mark which KEK produced it.
+ */
+
+const KEK_LENGTH_BYTES = 32; // AES-256
+const IV_LENGTH_BYTES = 12; // AES-GCM standard
+const MK_LENGTH_BYTES = 32; // user master key is also AES-256
+
+let _kek: CryptoKey | null = null;
+let _kekId: string | null = null;
+
+/**
+ * Loads the KEK from a base64 string and prepares it for use as an
+ * AES-GCM key. Idempotent: subsequent calls with the same string are
+ * no-ops. Throws if the input is not exactly 32 bytes after decoding.
+ *
+ * Call this once at boot from `index.ts` after `loadConfig()` has run.
+ */
+export async function loadKek(base64: string): Promise<void> {
+	if (_kek) return;
+
+	const raw = base64ToBytes(base64);
+	if (raw.length !== KEK_LENGTH_BYTES) {
+		throw new Error(
+			`mana-auth/kek: expected ${KEK_LENGTH_BYTES} bytes after base64 decode, got ${raw.length}. ` +
+				'Generate a fresh key with `openssl rand -base64 32`.'
+		);
+	}
+
+	// Loud warning if the dev fallback KEK (32 zero bytes) is in use —
+	// catches accidental production deploys without a real secret.
+	if (raw.every((b) => b === 0)) {
+		console.warn(
+			'\n⚠️  mana-auth: USING DEV KEK (32 zero bytes). ' +
+				'Set MANA_AUTH_KEK to a real value before production.\n'
+		);
+	}
+
+	_kek = await crypto.subtle.importKey(
+		'raw',
+		toBufferSource(raw),
+		{ name: 'AES-GCM', length: 256 },
+		false,
+		['encrypt', 'decrypt']
+	);
+
+	// kek_id format lets us distinguish env-loaded keys from future
+	// KMS-loaded ones at unwrap time. The `v1` suffix gives us a path
+	// for in-place rotation: a new KEK gets `env-v2`, old vault rows
+	// keep working until a background rotator re-wraps them.
+	_kekId = 'env-v1';
+}
+
+/** Returns the kek_id stamp written to encryption_vaults.kek_id. */
+export function activeKekId(): string {
+	if (!_kekId) throw new Error('mana-auth/kek: loadKek() not called yet');
+	return _kekId;
+}
+
+/**
+ * Wraps a 32-byte master key with the KEK. Returns the base64 IV and
+ * base64 ciphertext (which includes the 16-byte AES-GCM auth tag at
+ * the tail). Both pieces are written to `encryption_vaults`.
+ */
+export async function wrapMasterKey(
+	mkBytes: Uint8Array
+): Promise<{ wrappedMk: string; wrapIv: string }> {
+	if (mkBytes.length !== MK_LENGTH_BYTES) {
+		throw new Error(
+			`mana-auth/kek: expected ${MK_LENGTH_BYTES}-byte master key, got ${mkBytes.length}`
+		);
+	}
+	const kek = requireKek();
+	const iv = crypto.getRandomValues(new Uint8Array(IV_LENGTH_BYTES));
+	const ct = await crypto.subtle.encrypt(
+		{ name: 'AES-GCM', iv: toBufferSource(iv) },
+		kek,
+		toBufferSource(mkBytes)
+	);
+	return {
+		wrappedMk: bytesToBase64(new Uint8Array(ct)),
+		wrapIv: bytesToBase64(iv),
+	};
+}
+
+/**
+ * Unwraps a stored master key. Returns the raw 32 bytes ready to be
+ * sent to the client (over HTTPS) and re-imported as a CryptoKey by
+ * the browser.
+ *
+ * Throws on tampered ciphertext (auth tag mismatch), wrong IV length,
+ * wrong KEK, or any AES-GCM failure. The caller (vault service)
+ * surfaces these as 500s and writes a `failed_fetch` audit row.
+ */
+export async function unwrapMasterKey(wrappedMk: string, wrapIv: string): Promise<Uint8Array> {
+	const kek = requireKek();
+	const iv = base64ToBytes(wrapIv);
+	if (iv.length !== IV_LENGTH_BYTES) {
+		throw new Error(`mana-auth/kek: expected ${IV_LENGTH_BYTES}-byte IV, got ${iv.length}`);
+	}
+	const ct = base64ToBytes(wrappedMk);
+	const plain = await crypto.subtle.decrypt(
+		{ name: 'AES-GCM', iv: toBufferSource(iv) },
+		kek,
+		toBufferSource(ct)
+	);
+	const out = new Uint8Array(plain);
+	if (out.length !== MK_LENGTH_BYTES) {
+		throw new Error(
+			`mana-auth/kek: unwrapped key has wrong length ${out.length} (expected ${MK_LENGTH_BYTES})`
+		);
+	}
+	return out;
+}
+
+/**
+ * Generates a fresh 32-byte master key. Used by the vault service at
+ * vault initialisation time and during rotation.
+ */
+export function generateMasterKey(): Uint8Array {
+	return crypto.getRandomValues(new Uint8Array(MK_LENGTH_BYTES));
+}
+
+// ─── Internals ────────────────────────────────────────────────
+
+function requireKek(): CryptoKey {
+	if (!_kek) {
+		throw new Error('mana-auth/kek: loadKek() must be called before any wrap/unwrap operation');
+	}
+	return _kek;
+}
+
+function bytesToBase64(bytes: Uint8Array): string {
+	let bin = '';
+	for (let i = 0; i < bytes.length; i++) bin += String.fromCharCode(bytes[i]);
+	return btoa(bin);
+}
+
+function base64ToBytes(b64: string): Uint8Array {
+	const bin = atob(b64);
+	const out = new Uint8Array(bin.length);
+	for (let i = 0; i < bin.length; i++) out[i] = bin.charCodeAt(i);
+	return out;
+}
+
+/** TS 5.7 compat — Uint8Array<ArrayBufferLike> isn't assignable to BufferSource. */
+function toBufferSource(bytes: Uint8Array): ArrayBuffer {
+	const buf = new ArrayBuffer(bytes.length);
+	new Uint8Array(buf).set(bytes);
+	return buf;
+}
+
+// Test-only reset hook so vitest can reload the KEK between tests
+// without re-running the whole module. Not exported from any barrel.
+export function _resetForTesting(): void {
+	_kek = null;
+	_kekId = null;
+}