nhyatt/putty-source
1
0
Fork 0
mirror of https://git.tartarus.org/simon/putty.git synced 2025-07-17 19:11:00 -05:00
Code Issues Projects Releases Wiki Activity

Replace random_byte() with random_read().

Browse Source 
This is in preparation for a PRNG revamp which will want to have a
well defined boundary for any given request-for-randomness, so that it
can destroy the evidence afterwards. So no more looping round calling
random_byte() and then stopping when we feel like it: now you say up
front how many random bytes you want, and call random_read() which
gives you that many in one go.

Most of the call sites that had to be fixed are fairly mechanical, and
quite a few ended up more concise afterwards. A few became more
cumbersome, such as mp_random_bits, in which the new API doesn't let
me load the random bytes directly into the target integer without
triggering undefined behaviour, so instead I have to allocate a
separate temporary buffer.

The _most_ interesting call site was in the PKCS#1 v1.5 padding code
in sshrsa.c (used in SSH-1), in which you need a stream of _nonzero_
random bytes. The previous code just looped on random_byte, retrying
if it got a zero. Now I'm doing a much more interesting thing with an
mpint, essentially scaling a binary fraction repeatedly to extract a
number in the range [0,255) and then adding 1 to it.
This commit is contained in:
Simon Tatham
2019-01-22 19:43:27 +00:00
parent 76aa3f6f7a
commit 628e794832
21 changed files with 108 additions and 101 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
sshecc.c
View File

@ -1269,8 +1269,8 @@ static void ssh_ecdhkex_w_setup(ecdh_key *dh)
static void ssh_ecdhkex_m_setup(ecdh_key *dh)
{
strbuf *bytes = strbuf_new();
for (size_t i = 0; i < dh->curve->fieldBytes; ++i)
put_byte(bytes, random_byte());
random_read(strbuf_append(bytes, dh->curve->fieldBytes),
dh->curve->fieldBytes);
bytes->u[0] &= 0xF8;
bytes->u[bytes->len-1] &= 0x7F;