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-rw-r--r--Documentation/file-format.md36
1 files changed, 30 insertions, 6 deletions
diff --git a/Documentation/file-format.md b/Documentation/file-format.md
index 04bd2fe..7cce72c 100644
--- a/Documentation/file-format.md
+++ b/Documentation/file-format.md
@@ -18,22 +18,46 @@ Data block, AES-SIV mode (used in reverse mode, or when explicitly enabled with
16 bytes SIV
1-4096 bytes encrypted data
-Full block overhead = 32/4096 = 1/128 = 0.78125 %
+Data block, XChaCha20-Poly1305 (enabled via `-init -xchacha`)
-Example: 1-byte file
---------------------
+ 24 bytes nonce
+ 1-4096 bytes encrypted data
+ 16 bytes Poly1305 tag
+
+Full block overhead (AES-GCM and AES-SIV mode) = 32/4096 = 1/128 = 0.78125 %
+
+Full block overhead (XChaCha20-Poly1305 mode) = 40/4096 = \~1 %
+
+Example: 1-byte file, AES-GCM and AES-SIV mode
+----------------------------------------------
Header 18 bytes
Data block 33 bytes
Total: 51 bytes
-
-Example: 5000-byte file
------------------------
+Example: 5000-byte file, , AES-GCM and AES-SIV mode
+---------------------------------------------------
Header 18 bytes
Data block 4128 bytes
Data block 936 bytes
Total: 5082 bytes
+
+Example: 1-byte file, XChaCha20-Poly1305 mode
+----------------------------------------------
+
+ Header 18 bytes
+ Data block 41 bytes
+
+Total: 59 bytes
+
+Example: 5000-byte file, XChaCha20-Poly1305 mode
+----------------------------------------------
+
+ Header 18 bytes
+ Data block 4136 bytes
+ Data block 944 bytes
+
+Total: 5098 bytes