From b385520f21d8fc91964f222906877d24b9f253d1 Mon Sep 17 00:00:00 2001
From: Christoph Wurst <christoph@winzerhof-wurst.at>
Date: Wed, 27 Nov 2024 19:19:36 +0100
Subject: [PATCH] fix(migration): Decrypt ownCloud secrets v2

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>
---
 lib/private/Security/Crypto.php   | 32 ++++++++++++++++++++++++++++---
 tests/lib/Security/CryptoTest.php | 13 +++++++++++++
 2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/lib/private/Security/Crypto.php b/lib/private/Security/Crypto.php
index b03f8a4ddce14..58f921222dd54 100644
--- a/lib/private/Security/Crypto.php
+++ b/lib/private/Security/Crypto.php
@@ -114,6 +114,25 @@ private function decryptWithoutSecret(string $authenticatedCiphertext, string $p
 			throw new Exception('Authenticated ciphertext could not be decoded.');
 		}
 
+		/*
+		 * Rearrange arguments for legacy ownCloud migrations
+		 *
+		 * The original scheme consistent of three parts. Nextcloud added a
+		 * fourth at the end as "2" or later "3", ownCloud added "v2" at the
+		 * beginning.
+		 */
+		$originalParts = $parts;
+		$isOwnCloudV2Migration = $partCount === 4 && $originalParts[0] === 'v2';
+		if ($isOwnCloudV2Migration) {
+			$parts = [
+				$parts[1],
+				$parts[2],
+				$parts[3],
+				'2'
+			];
+		}
+
+		// Convert hex-encoded values to binary
 		$ciphertext = $this->hex2bin($parts[0]);
 		$iv = $parts[1];
 		$hmac = $this->hex2bin($parts[2]);
@@ -124,7 +143,7 @@ private function decryptWithoutSecret(string $authenticatedCiphertext, string $p
 				$iv = $this->hex2bin($iv);
 			}
 
-			if ($version === '3') {
+			if ($version === '3' || $isOwnCloudV2Migration) {
 				$keyMaterial = hash_hkdf('sha512', $password);
 				$encryptionKey = substr($keyMaterial, 0, 32);
 				$hmacKey = substr($keyMaterial, 32);
@@ -133,8 +152,15 @@ private function decryptWithoutSecret(string $authenticatedCiphertext, string $p
 		$this->cipher->setPassword($encryptionKey);
 		$this->cipher->setIV($iv);
 
-		if (!hash_equals($this->calculateHMAC($parts[0] . $parts[1], $hmacKey), $hmac)) {
-			throw new Exception('HMAC does not match.');
+		if ($isOwnCloudV2Migration) {
+			// ownCloud uses the binary IV for HMAC calculation
+			if (!hash_equals($this->calculateHMAC($parts[0] . $iv, $hmacKey), $hmac)) {
+				throw new Exception('HMAC does not match.');
+			}
+		} else {
+			if (!hash_equals($this->calculateHMAC($parts[0] . $parts[1], $hmacKey), $hmac)) {
+				throw new Exception('HMAC does not match.');
+			}
 		}
 
 		$result = $this->cipher->decrypt($ciphertext);
diff --git a/tests/lib/Security/CryptoTest.php b/tests/lib/Security/CryptoTest.php
index b65a9a36985b7..c67c478dd1f2b 100644
--- a/tests/lib/Security/CryptoTest.php
+++ b/tests/lib/Security/CryptoTest.php
@@ -88,6 +88,19 @@ public function testVersion2CiphertextDecryptsToCorrectPlaintext() {
 		);
 	}
 
+	/**
+	 * Test data taken from https://github.com/owncloud/core/blob/9deb8196b20354c8de0cd720ad4d18d52ccc96d8/tests/lib/Security/CryptoTest.php#L56-L60
+	 */
+	public function testOcVersion2CiphertextDecryptsToCorrectPlaintext() {
+		$this->assertSame(
+			'Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt.',
+			$this->crypto->decrypt(
+				'v2|d57dbe4d1317cdf19d4ddc2df807f6b5d63ab1e119c46590ce54bae56a9cd3969168c4ec1600ac9758dd7e7afb9c4c962dd23072c1463add1d9c77c467723b37bb768ef00e3c50898e59247cbb59ce56b74ce5990648ffe9e40d0e95076c27a785bdcf32c219ea4ad5c316b1f12f48c1|6bd21db258a5e406a2c288a444de195f|a19111a4cf1a11ee95fc1734699c20964eaa05bb007e1cecc4cc6872f827a4b7deedc977c13b138d728d68116aa3d82f9673e20c7e447a9788aa3be994b67cd6',
+				'ThisIsAVeryS3cur3P4ssw0rd'
+			)
+		);
+	}
+
 	public function testVersion3CiphertextDecryptsToCorrectPlaintext() {
 		$this->assertSame(
 			'Another plaintext value that will be encrypted with version 3. It addresses the related key issue. Old ciphertexts should be decrypted properly, but only use the better version for encryption.',