From 1a2d1484823cc4170b3da85bf8d7a08f287dab3b Mon Sep 17 00:00:00 2001
From: Audric Ackermann <audric@loki.network>
Date: Fri, 5 Mar 2021 16:55:25 +1100
Subject: [PATCH] add attachment padding

---
 ts/receiver/attachments.ts      | 14 ++++++--
 ts/session/utils/Attachments.ts | 57 +++++++++++++++++++++++++++++++--
 2 files changed, 66 insertions(+), 5 deletions(-)

diff --git a/ts/receiver/attachments.ts b/ts/receiver/attachments.ts
index c67497594..598436dec 100644
--- a/ts/receiver/attachments.ts
+++ b/ts/receiver/attachments.ts
@@ -3,6 +3,7 @@ import _ from 'lodash';
 import { MessageModel } from '../models/message';
 import { saveMessage } from '../../ts/data/data';
 import { fromBase64ToArrayBuffer } from '../session/utils/String';
+import { AttachmentUtils } from '../session/utils';
 
 export async function downloadAttachment(attachment: any) {
   const serverUrl = new URL(attachment.url).origin;
@@ -70,9 +71,16 @@ export async function downloadAttachment(attachment: any) {
     );
 
     if (!size || size !== data.byteLength) {
-      throw new Error(
-        `downloadAttachment: Size ${size} did not match downloaded attachment size ${data.byteLength}`
-      );
+      // we might have padding, check that all the remaining bytes are padding bytes
+      // otherwise we have an error.
+      if (AttachmentUtils.isLeftOfBufferPaddingOnly(data, size)) {
+        // we can safely remove the padding
+        data = data.slice(0, size);
+      } else {
+        throw new Error(
+          `downloadAttachment: Size ${size} did not match downloaded attachment size ${data.byteLength}`
+        );
+      }
     }
   }
 
diff --git a/ts/session/utils/Attachments.ts b/ts/session/utils/Attachments.ts
index f81ec0625..97e99b4e5 100644
--- a/ts/session/utils/Attachments.ts
+++ b/ts/session/utils/Attachments.ts
@@ -14,6 +14,7 @@ interface UploadParams {
   openGroup?: OpenGroup;
   isAvatar?: boolean;
   isRaw?: boolean;
+  shouldPad?: boolean;
 }
 
 interface RawPreview {
@@ -37,6 +38,8 @@ interface RawQuote {
 
 // tslint:disable-next-line: no-unnecessary-class
 export class AttachmentUtils {
+  public static readonly PADDING_BYTE = 0;
+
   private constructor() {}
 
   public static getDefaultServer(): LokiAppDotNetServerInterface {
@@ -44,7 +47,13 @@ export class AttachmentUtils {
   }
 
   public static async upload(params: UploadParams): Promise<AttachmentPointer> {
-    const { attachment, openGroup, isAvatar = false, isRaw = false } = params;
+    const {
+      attachment,
+      openGroup,
+      isAvatar = false,
+      isRaw = false,
+      shouldPad = false,
+    } = params;
     if (typeof attachment !== 'object' || attachment == null) {
       throw new Error('Invalid attachment passed.');
     }
@@ -83,8 +92,12 @@ export class AttachmentUtils {
       server = this.getDefaultServer();
       pointer.key = new Uint8Array(crypto.randomBytes(64));
       const iv = new Uint8Array(crypto.randomBytes(16));
+
+      const dataToEncrypt = !shouldPad
+        ? attachment.data
+        : AttachmentUtils.addAttachmentPadding(attachment.data);
       const data = await window.textsecure.crypto.encryptAttachment(
-        attachment.data,
+        dataToEncrypt,
         pointer.key.buffer,
         iv.buffer
       );
@@ -126,6 +139,7 @@ export class AttachmentUtils {
       this.upload({
         attachment,
         openGroup,
+        shouldPad: true,
       })
     );
 
@@ -181,4 +195,43 @@ export class AttachmentUtils {
       attachments,
     };
   }
+
+  public static isLeftOfBufferPaddingOnly(
+    data: ArrayBuffer,
+    unpaddedExpectedSize: number
+  ): boolean {
+    // to have a padding we must have a strictly longer length expected
+    if (data.byteLength <= unpaddedExpectedSize) {
+      return false;
+    }
+    const dataUint = new Uint8Array(data);
+    for (let i = unpaddedExpectedSize; i < data.byteLength; i++) {
+      if (dataUint[i] !== this.PADDING_BYTE) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  private static addAttachmentPadding(data: ArrayBuffer): ArrayBuffer {
+    const originalUInt = new Uint8Array(data);
+
+    const paddedSize = Math.max(
+      541,
+      Math.floor(
+        Math.pow(
+          1.05,
+          Math.ceil(Math.log(originalUInt.length) / Math.log(1.05))
+        )
+      )
+    );
+    const paddedData = new ArrayBuffer(paddedSize);
+    const paddedUInt = new Uint8Array(paddedData);
+
+    paddedUInt.fill(AttachmentUtils.PADDING_BYTE, originalUInt.length);
+    paddedUInt.set(originalUInt);
+
+    return paddedUInt.buffer;
+  }
 }