From 91d3b30c1c813a56ae057a373f045803fb788d60 Mon Sep 17 00:00:00 2001 From: Jakob Unterwurzacher Date: Thu, 26 Aug 2021 08:43:41 +0200 Subject: [PATCH] doc: file-format.md: describe XChaCha20-Poly1305 Different nonce size. --- Documentation/file-format.md | 36 ++++++++++++++++++++++++++++++------ 1 file 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