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Co-authored-by: Fedor Indutnyy <indutny@signal.org>

ts/Crypto.ts

@@ -454,8 +454,8 @@ export function decryptAttachment(
 }
 
 export function encryptAttachment(
-  plaintext: Uint8Array,
-  keys: Uint8Array
+  plaintext: Readonly<Uint8Array>,
+  keys: Readonly<Uint8Array>
 ): EncryptedAttachment {
   if (!(plaintext instanceof Uint8Array)) {
     throw new TypeError(
@@ -485,6 +485,24 @@ export function encryptAttachment(
   };
 }
 
+export function getAttachmentSizeBucket(size: number): number {
+  return Math.max(
+    541,
+    Math.floor(1.05 ** Math.ceil(Math.log(size) / Math.log(1.05)))
+  );
+}
+
+export function padAndEncryptAttachment(
+  data: Readonly<Uint8Array>,
+  keys: Readonly<Uint8Array>
+): EncryptedAttachment {
+  const size = data.byteLength;
+  const paddedSize = getAttachmentSizeBucket(size);
+  const padding = getZeroes(paddedSize - size);
+
+  return encryptAttachment(Bytes.concatenate([data, padding]), keys);
+}
+
 export function encryptProfile(data: Uint8Array, key: Uint8Array): Uint8Array {
   const iv = getRandomBytes(PROFILE_IV_LENGTH);
   if (key.byteLength !== PROFILE_KEY_LENGTH) {