file-format.md: document AES-SIV block layout

Fixes https://github.com/rfjakob/gocryptfs/issues/299
This commit is contained in:
Jakob Unterwurzacher 2019-01-04 19:31:41 +01:00
parent 28584d0d2c
commit 8c18fb5db9
1 changed files with 7 additions and 1 deletions

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@ -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