The old 'Bignum' data type is gone completely, and so is sshbn.c. In
its place is a new thing called 'mp_int', handled by an entirely new
library module mpint.c, with API differences both large and small.
The main aim of this change is that the new library should be free of
timing- and cache-related side channels. I've written the code so that
it _should_ - assuming I haven't made any mistakes - do all of its
work without either control flow or memory addressing depending on the
data words of the input numbers. (Though, being an _arbitrary_
precision library, it does have to at least depend on the sizes of the
numbers - but there's a 'formal' size that can vary separately from
the actual magnitude of the represented integer, so if you want to
keep it secret that your number is actually small, it should work fine
to have a very long mp_int and just happen to store 23 in it.) So I've
done all my conditionalisation by means of computing both answers and
doing bit-masking to swap the right one into place, and all loops over
the words of an mp_int go up to the formal size rather than the actual
size.
I haven't actually tested the constant-time property in any rigorous
way yet (I'm still considering the best way to do it). But this code
is surely at the very least a big improvement on the old version, even
if I later find a few more things to fix.
I've also completely rewritten the low-level elliptic curve arithmetic
from sshecc.c; the new ecc.c is closer to being an adjunct of mpint.c
than it is to the SSH end of the code. The new elliptic curve code
keeps all coordinates in Montgomery-multiplication transformed form to
speed up all the multiplications mod the same prime, and only converts
them back when you ask for the affine coordinates. Also, I adopted
extended coordinates for the Edwards curve implementation.
sshecc.c has also had a near-total rewrite in the course of switching
it over to the new system. While I was there, I've separated ECDSA and
EdDSA more completely - they now have separate vtables, instead of a
single vtable in which nearly every function had a big if statement in
it - and also made the externally exposed types for an ECDSA key and
an ECDH context different.
A minor new feature: since the new arithmetic code includes a modular
square root function, we can now support the compressed point
representation for the NIST curves. We seem to have been getting along
fine without that so far, but it seemed a shame not to put it in,
since it was suddenly easy.
In sshrsa.c, one major change is that I've removed the RSA blinding
step in rsa_privkey_op, in which we randomise the ciphertext before
doing the decryption. The purpose of that was to avoid timing leaks
giving away the plaintext - but the new arithmetic code should take
that in its stride in the course of also being careful enough to avoid
leaking the _private key_, which RSA blinding had no way to do
anything about in any case.
Apart from those specific points, most of the rest of the changes are
more or less mechanical, just changing type names and translating code
into the new API.
This is a heavily rewritten version of a patch originally by Lorenz
Diener; it was tidied up somewhat by Christian Brabandt, and then
tidied up more by me. The basic idea is to add to the termchar
structure a pair of small structs encoding 24-bit RGB values, each
with a flag indicating whether it's turned on; if it is, it overrides
any other specification of fg or bg colour for that character cell.
I've added a test line to colours.txt containing a few example colours
from /usr/share/X11/rgb.txt. In fact it makes quite a good demo to run
the whole of rgb.txt through this treatment, with a command such as
perl -pe 's!^\s*(\d+)\s+(\d+)\s+(\d+).*$!\e[38;2;$1;$2;$3m$&\e[m!' rgb.txt
I generated these as a by-product of using afl-fuzz on the testbn
executable. I'd hoped it would find interesting bugs in the bignum
code itself, but in fact it mostly found bugs in the parsing code in
the test main(). However, even so, it did produce a list of tests
which reach as much of the code as afl-fuzz was able to, and that
seems like a useful thing to save.
Also, of course, just having a place to put explicitly specified
bignum tests is a good thing anyway, because then we can put
regression tests on the end of it every time we fix bugs.
I'm about to rewrite the division code, so it'll be useful to have a
way to test it directly, particularly one which exercises difficult
cases such as extreme values of the leading word and remainders just
above and below zero.
mostly so I can valgrind both and make sure they free all their
workspace - a memory leak in this code would be not merely an
inconvenience but a security hazard.
[originally from svn r9101]
testdata/bignum.py is twice the size of the rest of the PuTTY source
put together, so I'm not checking it in.
This reveals bugs in the new multiplication code, which I have yet to
fix.
[originally from svn r9097]
incorrect. I must have written that binary search idiom a hundred
times, so it's rather embarrassing that I can't _automatically_ get
it right! This was causing all kinds of characters to be classified
as ON when they should have been various other classes.
Also while I'm here, I've added another test case to utf8.txt (a
small piece of Arabic within a predominantly L->R line), and also
supplied a means to compile minibidi.c with -DTEST_GETTYPE to
produce a command-line character class lookup tool. (Not sure what
use that'll be _other_ than debugging this precise problem, but I
don't like to throw it away now I've written it :-)
[originally from svn r5016]
going through the line and working out which bits need to be redrawn
is now in a separate loop from the subsequent activity of actually
going through and doing the redraws. This _should_ enable me to
tinker with the which-bits-to-redraw data in between the two, thus
fixing `font-overflow'. However, I thought it would be sensible to
break the work up into two commits so we can track bugs in the
restructuring separately from bugs introduced by the new feature.
Also added a couple more terminal test files.
[originally from svn r5001]
