From d739a920c91b8fbc9ce39e11e84e76d54dc5531e Mon Sep 17 00:00:00 2001
From: "Kyle J. McKay" <mackyle@gmail.com>
Date: Mon, 28 Jan 2019 23:35:25 -0700
Subject: [PATCH] User.pm: kindly suggest too large keys are unfriendly

There's no compelling reason to allow keys larger than 16384 bits
in length.  In fact, an RSA key of 15360 bits in length provides
an equivalent security strength of 256 bits; perhaps that should
be the maximum, but some software does round up and allow 16384 bits
so we'll go ahead and allow up to that long.

The handshake for very long keys imposes a computational burden on
the server so it behooves us to put a maximum in place to avoid
any unfortunate DOS attacks with regard to that.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>
---
 Girocco/User.pm | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Girocco/User.pm b/Girocco/User.pm
index a1d9dfe..c2d88fe 100644
--- a/Girocco/User.pm
+++ b/Girocco/User.pm
@@ -293,6 +293,13 @@ EOT
 Your ssh key ("$keyval") appears to be of type dsa but only rsa keys are
 supported - please generate an rsa key (starts with ssh-rsa) and try again
 EOT
+		} elsif ($bits > 16384) {
+			my $keyval = CGI::escapeHTML($key);
+			$gcgi->err(<<EOT);
+Your ssh key ("$keyval") appears to have more than 16384 bits, please don't
+unnecessarily overburden our processors - please limit yourself to keys of
+16384 bits or less.
+EOT
 		} elsif ($Girocco::Config::min_key_length && $bits < $Girocco::Config::min_key_length) {
 			my $keyval = CGI::escapeHTML($key);
 			$gcgi->err(<<EOT);
-- 
2.11.4.GIT