X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/25936864e19fb2749046c93e6e93148b758b89bc..f654f4218ac36981a1174b1f09823997239b0358:/papers/rand.tex

diff --git a/papers/rand.tex b/papers/rand.tex
index eda970e..1c489cc 100644
--- a/papers/rand.tex
+++ b/papers/rand.tex
@@ -1,6 +1,6 @@
 %%% -*-latex-*-
 %%%
-%%% $Id: rand.tex,v 1.2 1999/10/12 21:00:34 mdw Exp $
+%%% $Id: rand.tex,v 1.3 1999/10/15 21:05:56 mdw Exp $
 %%%
 %%% Description of Catacomb's random number generator
 %%%
@@ -29,6 +29,9 @@
 %%%----- Revision history ---------------------------------------------------
 %%%
 %%% $Log: rand.tex,v $
+%%% Revision 1.3  1999/10/15 21:05:56  mdw
+%%% Add a little more explanatory text for the pool and buffer sizes.
+%%%
 %%% Revision 1.2  1999/10/12 21:00:34  mdw
 %%% Updated.  Almost finished, in fact. ;-)
 %%%
@@ -200,13 +203,24 @@ The Catacomb implementation of the generator uses the following parameters:
 \item The hash function used in the one-way transformation is RIPEMD-160
   \cite{rmd160}; the block cipher is Blowfish, using a 160-bit key.
 \item The input pool size $N_I$ is 128 bytes.  The output buffer size $N_O$
-  is also 128 bytes.  The size $N_S$ of the secret part of the output buffer
+  is 512 bytes.  The size $N_S$ of the secret part of the output buffer
   is 160 bits (20 bytes).
 \item The polynomial $P(x)$ used for mixing in new input is
   $1 + x + x^2 + x^7 + x^{128}$.
 \end{itemize}
 The hash and block cipher are well-known and respected cryptographic
-primitives.  
+primitives.
+
+The input pool is rater larger than it strictly needs to be to contain
+`enough' entropy to bring the generator up to the strength of its
+cryptographic primitives.  The pool is large to reduce the effect of
+asymptotic behaviour in the amount of entropy in the pool.
+
+The output buffer is large simply to improve performance: Blowfish has a
+heavy key schedule, so it pays to perform fewer rekeyings per byte of data.
+The precise size of 512 bytes was chosen empirically as being about where the
+performance improvement stops being linear with the buffer size on my
+machine.
 
 \begin{thebibliography}{99}
   
