diff --git a/src/app.module.ts b/src/app.module.ts
index bbfc776..56b53c3 100644
--- a/src/app.module.ts
+++ b/src/app.module.ts
@@ -1,4 +1,5 @@
 import { Module } from '@nestjs/common';
+import { APP_GUARD } from '@nestjs/core';
 import { TypeOrmModule } from '@nestjs/typeorm';
 import { buildTypeOrmConfig } from './database.config';
 import { HealthController } from './common/health.controller';
@@ -7,15 +8,24 @@ import { MetricsService } from './common/metrics.service';
 import { AuthModule } from './auth/auth.module';
 import { NodesModule } from './nodes/nodes.module';
 import { AuditModule } from './audit/audit.module';
+import { CenterApiKeyGuard } from './common/center-api-key.guard';
+import { GuildNode } from './entities/guild-node.entity';
 
 @Module({
   imports: [
     TypeOrmModule.forRoot(buildTypeOrmConfig()),
+    TypeOrmModule.forFeature([GuildNode]),
     AuditModule,
     AuthModule,
     NodesModule,
   ],
   controllers: [HealthController, MetricsController],
-  providers: [MetricsService],
+  providers: [
+    MetricsService,
+    {
+      provide: APP_GUARD,
+      useClass: CenterApiKeyGuard,
+    },
+  ],
 })
 export class AppModule {}
diff --git a/src/common/center-api-key.guard.ts b/src/common/center-api-key.guard.ts
new file mode 100644
index 0000000..b53ad25
--- /dev/null
+++ b/src/common/center-api-key.guard.ts
@@ -0,0 +1,43 @@
+import { CanActivate, ExecutionContext, Injectable, UnauthorizedException } from '@nestjs/common';
+import { InjectRepository } from '@nestjs/typeorm';
+import { Repository } from 'typeorm';
+import * as bcrypt from 'bcryptjs';
+import { GuildNode } from '../entities/guild-node.entity';
+
+@Injectable()
+export class CenterApiKeyGuard implements CanActivate {
+  constructor(
+    @InjectRepository(GuildNode)
+    private readonly nodeRepo: Repository<GuildNode>,
+  ) {}
+
+  async canActivate(context: ExecutionContext): Promise<boolean> {
+    const req = context.switchToHttp().getRequest<{
+      path?: string;
+      method?: string;
+      headers: Record<string, string | string[] | undefined>;
+    }>();
+
+    const path = req.path ?? '';
+    const method = (req.method ?? 'GET').toUpperCase();
+
+    // only guild registration is exempt from API key; it is protected by HMAC secret
+    if (method === 'POST' && (path === '/nodes/register' || path.endsWith('/nodes/register'))) {
+      return true;
+    }
+
+    const received = req.headers['x-api-key'];
+    const apiKey = Array.isArray(received) ? received[0] : received;
+    if (!apiKey) throw new UnauthorizedException('missing api key');
+
+    const nodes = await this.nodeRepo.find({ where: { status: 'active' } });
+    for (const node of nodes) {
+      if (!node.apiKeyHash) continue;
+      const ok = await bcrypt.compare(apiKey, node.apiKeyHash);
+      if (ok) return true;
+    }
+
+    throw new UnauthorizedException('invalid api key');
+  }
+}
+
diff --git a/src/entities/guild-node.entity.ts b/src/entities/guild-node.entity.ts
index a79c2ba..92ca27e 100644
--- a/src/entities/guild-node.entity.ts
+++ b/src/entities/guild-node.entity.ts
@@ -20,6 +20,9 @@ export class GuildNode {
   @Column()
   endpoint!: string;
 
+  @Column({ type: 'varchar', length: 255, nullable: true })
+  apiKeyHash!: string | null;
+
   @Column({
     type: 'enum',
     enum: ['active', 'offline', 'revoked'],
diff --git a/src/nodes/nodes.controller.ts b/src/nodes/nodes.controller.ts
index b150778..3f73188 100644
--- a/src/nodes/nodes.controller.ts
+++ b/src/nodes/nodes.controller.ts
@@ -16,6 +16,8 @@ import {
 } from '@nestjs/common';
 import { InjectRepository } from '@nestjs/typeorm';
 import { Repository } from 'typeorm';
+import * as bcrypt from 'bcryptjs';
+import { randomBytes } from 'crypto';
 import { GuildNode } from '../entities/guild-node.entity';
 import { AuditService } from '../audit/audit.service';
 import { RegisterNodeDto } from './dto.register-node.dto';
@@ -95,7 +97,10 @@ export class NodesController {
       name: body.name,
       endpoint: body.endpoint,
       status: 'active',
+      apiKeyHash: null,
     });
+    const rawApiKey = `gk_${randomBytes(24).toString('hex')}`;
+    node.apiKeyHash = await bcrypt.hash(rawApiKey, 10);
     const saved = await this.nodeRepo.save(node);
     await this.audit.write({
       action: 'node.register',
@@ -114,6 +119,7 @@ export class NodesController {
         endpoint: saved.endpoint,
         status: saved.status,
       },
+      apiKey: rawApiKey,
     };
   }