From 2b7cf212bb2e179294a4190745dbe003d971bc46 Mon Sep 17 00:00:00 2001
From: Roeland Jago Douma <roeland@famdouma.nl>
Date: Tue, 9 Feb 2021 16:42:21 +0100
Subject: [PATCH 1/2] Move to AES-256-GCM for openssl_seal/open

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>
---
 apps/encryption/lib/Crypto/Crypt.php | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/apps/encryption/lib/Crypto/Crypt.php b/apps/encryption/lib/Crypto/Crypt.php
index f8ba3d69b80f8..dbbd8df1dc8ec 100644
--- a/apps/encryption/lib/Crypto/Crypt.php
+++ b/apps/encryption/lib/Crypto/Crypt.php
@@ -707,11 +707,25 @@ public function multiKeyDecrypt($encKeyFile, $shareKey, $privateKey) {
 			throw new MultiKeyDecryptException('Cannot multikey decrypt empty plain content');
 		}
 
+		$prev = null;
+
+		// We need to be able to extract the IV
+		if (strlen($encKeyFile) > 12) {
+			$iv = substr($encKeyFile, -12);
+			$encrypted = substr($encKeyFile, 0, -12);
+
+			if (openssl_open($encrypted, $plainContent, $shareKey, $privateKey, 'aes-256-gcm', $iv)) {
+				return $plainContent;
+			}
+
+			$prev = new MultiKeyDecryptException('multikeydecrypt with share key failed (aes-256-gcm):' . openssl_error_string());
+		}
+
 		if (openssl_open($encKeyFile, $plainContent, $shareKey, $privateKey, 'RC4')) {
 			return $plainContent;
-		} else {
-			throw new MultiKeyDecryptException('multikeydecrypt with share key failed:' . openssl_error_string());
 		}
+
+		throw new MultiKeyDecryptException('multikeydecrypt with share key failed (rc4):' . openssl_error_string(), '', 0, $prev);
 	}
 
 	/**
@@ -732,7 +746,8 @@ public function multiKeyEncrypt($plainContent, array $keyFiles) {
 		$shareKeys = [];
 		$mappedShareKeys = [];
 
-		if (openssl_seal($plainContent, $sealed, $shareKeys, $keyFiles, 'RC4')) {
+		$iv = \random_bytes(12);
+		if (openssl_seal($plainContent, $sealed, $shareKeys, $keyFiles, 'aes-256-gcm', $iv)) {
 			$i = 0;
 
 			// Ensure each shareKey is labelled with its corresponding key id
@@ -742,12 +757,11 @@ public function multiKeyEncrypt($plainContent, array $keyFiles) {
 			}
 
 			return [
-				'keys' => $mappedShareKeys,
+				'keys' => $mappedShareKeys . $iv,
 				'data' => $sealed
 			];
-		} else {
-			throw new MultiKeyEncryptException('multikeyencryption failed ' . openssl_error_string());
 		}
+		throw new MultiKeyEncryptException('multikeyencryption failed ' . openssl_error_string());
 	}
 
 	public function useLegacyBase64Encoding(): bool {

From 905e6d8d8d5f474490922e062c2f014a31d05ed0 Mon Sep 17 00:00:00 2001
From: Roeland Jago Douma <roeland@famdouma.nl>
Date: Tue, 9 Feb 2021 19:33:05 +0100
Subject: [PATCH 2/2] fixup! Move to AES-256-GCM for openssl_seal/open

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>
---
 apps/encryption/lib/Crypto/Crypt.php | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/apps/encryption/lib/Crypto/Crypt.php b/apps/encryption/lib/Crypto/Crypt.php
index dbbd8df1dc8ec..16d4c24f22866 100644
--- a/apps/encryption/lib/Crypto/Crypt.php
+++ b/apps/encryption/lib/Crypto/Crypt.php
@@ -757,8 +757,8 @@ public function multiKeyEncrypt($plainContent, array $keyFiles) {
 			}
 
 			return [
-				'keys' => $mappedShareKeys . $iv,
-				'data' => $sealed
+				'keys' => $mappedShareKeys,
+				'data' => $sealed . $iv,
 			];
 		}
 		throw new MultiKeyEncryptException('multikeyencryption failed ' . openssl_error_string());