diff --git a/keyserver/src/uploads/uploads.js b/keyserver/src/uploads/uploads.js
--- a/keyserver/src/uploads/uploads.js
+++ b/keyserver/src/uploads/uploads.js
@@ -57,6 +57,17 @@
 
   const inputLoop = !!(files.length === 1 && body.loop);
 
+  const inputEncryptionKey =
+    files.length === 1 && body.encryptionKey ? body.encryptionKey : null;
+  if (inputEncryptionKey && typeof inputEncryptionKey !== 'string') {
+    throw new ServerError('invalid_parameters');
+  }
+  const inputMimeType =
+    files.length === 1 && body.mimeType ? body.mimeType : null;
+  if (inputMimeType && typeof inputMimeType !== 'string') {
+    throw new ServerError('invalid_parameters');
+  }
+
   const validationResults = await Promise.all(
     files.map(({ buffer, size, originalname }) =>
       validateAndConvert(
diff --git a/lib/actions/upload-actions.js b/lib/actions/upload-actions.js
--- a/lib/actions/upload-actions.js
+++ b/lib/actions/upload-actions.js
@@ -13,7 +13,11 @@
   abortHandler: (abort: () => void) => void,
   uploadBlob: UploadBlob,
 }>;
-export type MultimediaUploadExtras = Shape<{ ...Dimensions, loop: boolean }>;
+export type MultimediaUploadExtras = Shape<{
+  ...Dimensions,
+  loop: boolean,
+  encryptionKey?: string,
+}>;
 
 const uploadMultimedia =
   (
@@ -38,6 +42,14 @@
     if (extras.loop) {
       stringExtras.loop = '1';
     }
+    if (extras.encryptionKey) {
+      stringExtras.encryptionKey = extras.encryptionKey;
+    }
+
+    // also pass MIME type if available
+    if (multimedia.type && typeof multimedia.type === 'string') {
+      stringExtras.mimeType = multimedia.type;
+    }
 
     const response = await callServerEndpoint(
       'upload_multimedia',