Right now, all our curve25519 backends ignore the high bit of the
public key. But possibly, others could treat the high bit of the
public key as encoding out-of-bounds values, or as something to be
preserved. This could be used to distinguish clients with different
backends, at the cost of killing a circuit.
As a workaround, let's just clear the high bit of each public key
indiscriminately before we use it. Fix for bug 8121, reported by
rransom. Bugfix on 0.2.4.8-alpha.
Previously, we only used the strong OS entropy source as part of
seeding OpenSSL's RNG. But with curve25519, we'll have occasion to
want to generate some keys using extremely-good entopy, as well as the
means to do so. So let's!
This patch refactors the OS-entropy wrapper into its own
crypto_strongest_rand() function, and makes our new
curve25519_secret_key_generate function try it as appropriate.
We want to use donna-c64 when we have a GCC with support for
64x64->uint128_t multiplying. If not, we want to use libnacl if we
can, unless it's giving us the unsafe "ref" implementation. And if
that isn't going to work, we'd like to use the
portable-and-safe-but-slow 32-bit "donna" implementation.
We might need more library searching for the correct libnacl,
especially once the next libnacl release is out -- it's likely to have
bunches of better curve25519 implementations.
I also define a set of curve25519 wrapper functions, though it really
shouldn't be necessary.
We should eventually make the -donna*.c files get build with
-fomit-frame-pointer, since that can make a difference.
This is a customizable extract-and-expand HMAC-KDF for deriving keys.
It derives from RFC5869, which derives its rationale from Krawczyk,
H., "Cryptographic Extraction and Key Derivation: The HKDF Scheme",
Proceedings of CRYPTO 2010, 2010, <http://eprint.iacr.org/2010/264>.
I'm also renaming the existing KDF, now that Tor has two of them.
This is the key derivation scheme specified in ntor.
There are also unit tests.
This is part of what's needed to build without warnings on mingw64:
it was warning about the cast from void* to long that happened in
the places we were using test_{n,}eq on pointers.
The alternative here would have been to broaden tt_int_op to accept
a long long or an intptr_t, but that's less correct (since pointers
aren't integers), and would hurt the portability of tinytest a
little.
Fixes part of 7260.
To solve bug 4779, we want to avoid OpenSSL 1.0.0's counter mode.
But Fedora (and maybe others) lie about the actual OpenSSL version,
so we can't trust the header to tell us if it's safe.
Instead, let's do a run-time test to see whether it's safe, and if
not, use our built-in version.
fermenthor contributed a pretty essential fixup to this patch. Thanks!
When we added the check for key size, we required that the keys be
128 bytes. But RSA_size (which defers to BN_num_bytes) will return
128 for keys of length 1017..1024. This patch adds a new
crypto_pk_num_bits() that returns the actual number of significant
bits in the modulus, and uses that to enforce key sizes.
Also, credit the original bug3318 in the changes file.
Most instances were dead code; for those, I removed the assignments.
Some were pieces of info we don't currently plan to use, but which
we might in the future. For those, I added an explicit cast-to-void
to indicate that we know that the thing's unused. Finally, one was
a case where we were testing the wrong variable in a unit test.
That one I fixed.
This resolves bug 3208.
Our regular DH parameters that we use for circuit and rendezvous
crypto are unchanged. This is yet another small step on the path of
protocol fingerprinting resistance.
See task 1114. The most plausible explanation for someone sending us weak
DH keys is that they experiment with their Tor code or implement a new Tor
client. Usually, we don't care about such events, especially not on warn
level. If we really care about someone not following the Tor protocol, we
can set ProtocolWarnings to 1.
