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diff --git a/native/media/encryption-utils.js b/native/media/encryption-utils.js
new file mode 100644
--- /dev/null
+++ b/native/media/encryption-utils.js
@@ -0,0 +1,191 @@
+// @flow
+
+import filesystem from 'react-native-fs';
+
+import { base64FromIntArray, hexToUintArray } from 'lib/media/data-utils.js';
+import { fileInfoFromData, readableFilename } from 'lib/media/file-utils.js';
+import type { MediaMissionFailure } from 'lib/types/media-types.js';
+import { getMessageForException } from 'lib/utils/errors.js';
+import { unpad } from 'lib/utils/pkcs7-padding.js';
+
+import { temporaryDirectoryPath } from './file-utils.js';
+import { getFetchableURI } from './identifier-utils.js';
+import * as AES from '../utils/aes-crypto-module.js';
+
+const PADDING_THRESHOLD = 5_000_000; // we don't pad files larger than this
+
+type DecryptFileStep =
+ | {
+ +step: 'fetch_file',
+ +file: string,
+ +time: number,
+ +success: boolean,
+ +exceptionMessage: ?string,
+ }
+ | {
+ +step: 'decrypt_data',
+ +dataSize: number,
+ +time: number,
+ +isPadded: boolean,
+ +success: boolean,
+ +exceptionMessage: ?string,
+ }
+ | {
+ +step: 'write_file',
+ +file: string,
+ +mimeType: string,
+ +time: number,
+ +success: boolean,
+ +exceptionMessage: ?string,
+ }
+ | {
+ +step: 'create_data_uri',
+ +mimeType: string,
+ +time: number,
+ +success: boolean,
+ +exceptionMessage: ?string,
+ };
+type DecryptionFailure =
+ | MediaMissionFailure
+ | {
+ +success: false,
+ +reason:
+ | 'fetch_file_failed'
+ | 'decrypt_data_failed'
+ | 'write_file_failed',
+ +exceptionMessage: ?string,
+ };
+
+async function decryptMedia(
+ holder: string,
+ encryptionKey: string,
+ options: { +destination: 'file' | 'data_uri' },
+): Promise<{
+ steps: $ReadOnlyArray<DecryptFileStep>,
+ result: DecryptionFailure | { success: true, uri: string },
+}> {
+ let success = true,
+ exceptionMessage;
+ const steps: DecryptFileStep[] = [];
+
+ // Step 1. Fetch the file and convert it to a Uint8Array
+ const fetchStartTime = Date.now();
+ let data;
+ try {
+ const response = await fetch(getFetchableURI(holder));
+ const buf = await response.arrayBuffer();
+ data = new Uint8Array(buf);
+ } catch (e) {
+ success = false;
+ exceptionMessage = getMessageForException(e);
+ }
+ steps.push({
+ step: 'fetch_file',
+ file: holder,
+ time: Date.now() - fetchStartTime,
+ success,
+ exceptionMessage,
+ });
+ if (!success || !data) {
+ return {
+ steps,
+ result: { success: false, reason: 'fetch_file_failed', exceptionMessage },
+ };
+ }
+
+ // Step 2. Decrypt the data
+ const decryptionStartTime = Date.now();
+ let plaintextData, decryptedData, isPadded;
+ try {
+ const key = hexToUintArray(encryptionKey);
+ plaintextData = AES.decrypt(key, data);
+ isPadded = plaintextData.byteLength <= PADDING_THRESHOLD;
+ decryptedData = isPadded ? unpad(plaintextData) : plaintextData;
+ } catch (e) {
+ success = false;
+ exceptionMessage = getMessageForException(e);
+ }
+ steps.push({
+ step: 'decrypt_data',
+ dataSize: decryptedData?.byteLength ?? -1,
+ isPadded: !!isPadded,
+ time: Date.now() - decryptionStartTime,
+ success,
+ exceptionMessage,
+ });
+
+ if (!success || !decryptedData) {
+ return {
+ steps,
+ result: {
+ success: false,
+ reason: 'decrypt_data_failed',
+ exceptionMessage,
+ },
+ };
+ }
+
+ // Step 3. Write the file to disk or create a data URI
+ let uri;
+ const writeStartTime = Date.now();
+ // we need extension for react-native-video to work
+ const { mime } = fileInfoFromData(decryptedData);
+ if (!mime) {
+ return {
+ steps,
+ result: {
+ success: false,
+ reason: 'mime_check_failed',
+ mime,
+ },
+ };
+ }
+ const base64 = base64FromIntArray(decryptedData);
+ if (options.destination === 'file') {
+ // if holder is a URL, then we use the last part of the path as the filename
+ const holderSuffix = holder.substring(holder.lastIndexOf('/') + 1);
+ const filename = readableFilename(holderSuffix, mime) || holderSuffix;
+ const targetPath = `${temporaryDirectoryPath}${Date.now()}-${filename}`;
+ try {
+ await filesystem.writeFile(targetPath, base64, 'base64');
+ } catch (e) {
+ success = false;
+ exceptionMessage = getMessageForException(e);
+ }
+ uri = `file://${targetPath}`;
+ steps.push({
+ step: 'write_file',
+ file: uri,
+ mimeType: mime,
+ time: Date.now() - writeStartTime,
+ success,
+ exceptionMessage,
+ });
+ if (!success) {
+ return {
+ steps,
+ result: {
+ success: false,
+ reason: 'write_file_failed',
+ exceptionMessage,
+ },
+ };
+ }
+ } else {
+ uri = `data:${mime};base64,${base64}`;
+ steps.push({
+ step: 'create_data_uri',
+ mimeType: mime,
+ time: Date.now() - writeStartTime,
+ success,
+ exceptionMessage,
+ });
+ }
+
+ return {
+ steps,
+ result: { success: true, uri },
+ };
+}
+
+export { decryptMedia };

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