Credit Emilia Käsper for the placeholder idea.

1 files changed, 10 insertions, 4 deletions

diff --git a/src/ht.erl b/src/ht.erl
index cd4e57c..7051b9e 100644
--- a/src/ht.erl
+++ b/src/ht.erl
@@ -6,18 +6,24 @@
 %%% follows RFC 6962 and differs from [0] only in how non-full trees
 %%% are handled.
 %%%
-%%% [0] https://www.usenix.org/event/sec09/tech/full_papers/crosby.pdf
+%%% The idea with placeholder nodes on incomplete layers is borrowed
+%%% from Emilia Käspers implementation in Google's
+%%% certificate-transparency project.
 %%%
-%%% Hashes of inner nodes and leaves are stored in arrays, one per
-%%% layer with layer 0 being where the leaves are. The total number of
-%%% arrays is equal to the depth of the tree. The depth of the tree is
+%%% Hashes of inner nodes and leaves are stored in whatever
+%%% datastructure the ts module uses, one per layer. Layer 0 is where
+%%% the leaves are. The total number of datastructures used in ts is
+%%% equal to the depth of the tree. The depth of the tree is
 %%% ceil(lg2(number of leaves)).
+%%%
 %%% Let {r,i} denote the hash with index i on layer r. The first leaf
 %%% is {0,0}, second is {0,1} and n:th is {0,n-1}.
 %%% The parent of {r,i} is {r+1,floor(i/2)} (not strictly true because
 %%% of "placeholder nodes", see update_parent/4).
 %%% The sibling of {r,i} is {r,i+1} when i is even and {r,i-1} when i
 %%% is odd.
+%%%
+%%% [0] https://www.usenix.org/event/sec09/tech/full_papers/crosby.pdf
 
 -module(ht).
 -behaviour(gen_server).