diff --git a/apps/backend/src/config.ts b/apps/backend/src/config.ts
index cd713b4..cab146f 100644
--- a/apps/backend/src/config.ts
+++ b/apps/backend/src/config.ts
@@ -15,6 +15,18 @@ export const EnvSchema = z.object({
   JWT_SECRET: z.string().min(1, 'JWT_SECRET is required'),
   PORT: z.coerce.number().int('PORT must be an integer').positive('PORT must be positive'),
   TOKEN_TRANSFER_CONTRACT_ID: z.string().min(1, 'TOKEN_TRANSFER_CONTRACT_ID is required'),
+  S3_ENDPOINT: z.string().optional(),
+  S3_REGION: z.string().optional(),
+  S3_ACCESS_KEY_ID: z.string().optional(),
+  S3_SECRET_ACCESS_KEY: z.string().optional(),
+  S3_BUCKET: z.string().optional(),
+  S3_FORCE_PATH_STYLE: z
+    .preprocess((val) => {
+      if (val === 'true' || val === true) return true;
+      if (val === 'false' || val === false) return false;
+      return undefined;
+    }, z.boolean())
+    .optional(),
   OBJECT_STORE_ENDPOINT: z.string().min(1, 'OBJECT_STORE_ENDPOINT is required'),
   OBJECT_STORE_BUCKET: z.string().min(1, 'OBJECT_STORE_BUCKET is required'),
   OBJECT_STORE_ACCESS_KEY: z.string().min(1, 'OBJECT_STORE_ACCESS_KEY is required'),
diff --git a/apps/backend/src/routes/files.ts b/apps/backend/src/routes/files.ts
index 76c354b..c8f5cf8 100644
--- a/apps/backend/src/routes/files.ts
+++ b/apps/backend/src/routes/files.ts
@@ -4,6 +4,7 @@ import { eq, and } from 'drizzle-orm';
 import { db } from '../db/index.js';
 import { messages, conversationMembers, files } from '../db/schema.js';
 import { requireAuth, type AuthRequest } from '../middleware/auth.js';
+import { objectStore } from '../lib/objectStore.js';
 import { S3Client, GetObjectCommand, PutObjectCommand } from '@aws-sdk/client-s3';
 import { getSignedUrl } from '@aws-sdk/s3-request-presigner';
 import { randomUUID } from 'node:crypto';
@@ -148,7 +149,7 @@ filesRouter.get('/:fileId', async (req: AuthRequest, res) => {
       Key: fileRecord.storageKey,
     });
     // Short-lived URL: 5 minutes
-    const presignedUrl = await getSignedUrl(s3, command, { expiresIn: 300 });
+    const presignedUrl = await objectStore.getDownloadUrl(fileId, 300);
     res.json({ url: presignedUrl });
   } catch {
     res.status(500).json({ error: 'Failed to generate download URL' });