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authorJakob Unterwurzacher2019-01-04 19:31:41 +0100
committerJakob Unterwurzacher2019-01-04 19:31:41 +0100
commit8c18fb5db9544486412c697a90ad55710639b36a (patch)
treea128c9c1a3793365e0eadff63aea6779225c0ac5
parent28584d0d2c829fa1824bebc13e446968ebdee6b6 (diff)
file-format.md: document AES-SIV block layout
Fixes https://github.com/rfjakob/gocryptfs/issues/299
-rw-r--r--Documentation/file-format.md8
1 files changed, 7 insertions, 1 deletions
diff --git a/Documentation/file-format.md b/Documentation/file-format.md
index ad1fb3f..5699f9e 100644
--- a/Documentation/file-format.md
+++ b/Documentation/file-format.md
@@ -6,12 +6,18 @@ Header
2 bytes header version (big endian uint16, currently 2)
16 bytes file id
-Data block
+Data block, default AES-GCM mode
16 bytes GCM IV (nonce)
1-4096 bytes encrypted data
16 bytes GHASH
+Data block, AES-SIV mode (used in reverse mode, or when explicitely enabled with `-init -aessiv`)
+
+ 16 bytes nonce
+ 16 bytes SIV
+ 1-4096 bytes encrypted data
+
Full block overhead = 32/4096 = 1/128 = 0.78125 %
Example: 1-byte file