From 0cf535b26c8989a60df646f64dfcb14b59de1a86 Mon Sep 17 00:00:00 2001
From: drebs <drebs@leap.se>
Date: Tue, 26 Dec 2017 08:48:18 -0200
Subject: [PATCH] [doc] improve documentation of ciphertext size estimation
function
---
src/leap/soledad/client/_crypto.py | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/src/leap/soledad/client/_crypto.py b/src/leap/soledad/client/_crypto.py
index ce166c94..ab5fe881 100644
--- a/src/leap/soledad/client/_crypto.py
+++ b/src/leap/soledad/client/_crypto.py
@@ -541,9 +541,17 @@ def _ceiling(size):
def get_unarmored_ciphertext_size(cleartext_size):
- # used for blobs stream up (so we can tell the server how much data we are
- # sending before starting to encrypt the stream)
+ """
+ Get the (unarmored) ciphertext size from the cleartext size.
+
+ In some cases (when streaming uploads, for example) we need to tell the
+ server how much data we are sending before starting to encrypt the stream.
+ This function returns the final size of what will be streamed from the
+ total size of the cleartext.
+ """
tag_size = 16 # AES-GCM 16-byte tag appended to ciphertext
separator_size = 1 # space separating content from preamble
size = tag_size + PREAMBLE_SIZE + separator_size
+ # without considering the preamble and tag, the ciphertext size is equal to
+ # the cleartext size.
return cleartext_size + size
--
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