Changes between Version 15 and Version 16 of help/en/howto/cryptomator

Timestamp:

Jan 9, 2017 12:43:04 PM (3 years ago)

Author:

yla

Comment:

--

help/en/howto/cryptomator

@@ -11 +11 @@
 Compared to other client-side-encryption solutions the [https://cryptomator.org Cryptomator] based approach yields a few crucial advantages:
 
-* in addition to file content encryption also filenames are encrypted and directory structures obfuscated
+* in addition to file content encryption also file and directory names are encrypted and directory structures obfuscated
 * no online services, no subscriptions, no accounts
 * no need to share your cloud storage provider credentials
@@ -24 +24 @@
  Both keys are encrypted using RFC 3394 key wrapping with a KEK derived from the user's password using scrypt.
 
-The wrapped keys are stored in a JSON file named `masterkey.cryptomator` located in the root directory of a vault.
-
-
+The wrapped keys (with some additional metadata) are remotely stored in a JSON file named `masterkey.cryptomator` located in the root directory of a vault.
 
 === Filename Encryption ===
-TBD.
-=== File Content Encryption ===
-TBD.
+ Cryptomator uses AES-SIV to encrypt file as well as directory names. Additionally to the name, a unique directory ID of its parent directory is passed as associated data. This prevents undetected moving of files between directories.
+
+=== File Header Encryption ===
+
+ The file header stores certain metadata, which is needed for file content encryption. It consists of 88 bytes.
+
+ * 16 bytes nonce used during header payload encryption
+ * 40 bytes AES-CTR encrypted payload consisting of:
+ * 8 bytes filled with 1 for future use (formerly used for file size)
+ * 32 bytes file content key
+ * 32 bytes header MAC of the previous 56 bytes
+
+ === File Content Encryption ===
+
+ The cleartext is broken down into multiple chunks, each up to 32 KiB + 48 bytes consisting of:
+
+ * 16 bytes nonce
+ * up to 32 KiB encrypted payload using AES-CTR with the file content key
+ * 32 bytes MAC of
+  * file header nonce (to bind this chunk to the file header)
+  * chunk number as 8 byte big endian integer (to prevent undetected reordering)
+  * nonce
+  * encrypted payload
 
 == Create new Vault ==