From 02482b695aa6589ccd4426bdeaaadf1ba05998d7 Mon Sep 17 00:00:00 2001 From: Daira Hopwood Date: Thu, 8 Feb 2018 01:18:31 +0000 Subject: [PATCH] Add note about endianness of repr_J. Signed-off-by: Daira Hopwood --- protocol/protocol.tex | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/protocol/protocol.tex b/protocol/protocol.tex index 6221d5e3..c5885bcd 100644 --- a/protocol/protocol.tex +++ b/protocol/protocol.tex @@ -4264,6 +4264,12 @@ Define $\reprJ \typecolon \GroupJ \rightarrow \bitseq{\ellJ}$ such that $\reprJ(u, \varv) = \ItoLEBSP{256}(\varv + 2^{255} \smult \tilde{u})$, where $\tilde{u} = u \bmod 2$. +\todo{Representing this as a bit string is problematic because we normally encode +most-significant-bit first within a byte, so that would result in the wrong +(i.e. non-standard) encoding as a byte sequence. It's a tricky specification +problem that we get away with elsewhere in the spec mostly by luck. Maybe keep +the representation as an integer?} + Let $\abstJ \typecolon \bitseq{\ellJ} \rightarrow \GroupJ \union \setof{\bot}$ be the left inverse of $\reprJ$ such that if $S$ is not in the range of $\reprJ$, then $\abstJ(S) = \bot$.