Commit f1d669aee994b28e1afcfe974680565932d25b70 added support for
AES_256_GCM_SHA384 cipher suites as specified in RFC5289. However, it
did not take the arbitrary hash function into account in the TLS client
handshake when using client certificates.
The hashForClientCertificate method always returned SHA256 as its
hashing function, even if it actually used a different one to calculate
its digest. Setting up the connection would eventually fail with the
error "tls: failed to sign handshake with client certificate:
crypto/rsa: input must be hashed message".
Included is an additional test for this specific situation that uses the
SHA384 hash.
Fixes#9808
Change-Id: Iccbf4ab225633471ef897907c208ad31f92855a3
Reviewed-on: https://go-review.googlesource.com/7040
Reviewed-by: Adam Langley <agl@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>
Generalizes PRF calculation for TLS 1.2 to support arbitrary hashes (SHA-384 instead of SHA-256).
Testdata were all updated to correspond with the new cipher suites in the handshake.
Change-Id: I3d9fc48c19d1043899e38255a53c80dc952ee08f
Reviewed-on: https://go-review.googlesource.com/3265
Reviewed-by: Adam Langley <agl@golang.org>
ECDSA is unsafe to use if an entropy source produces predictable
output for the ephemeral nonces. E.g., [Nguyen]. A simple
countermeasure is to hash the secret key, the message, and
entropy together to seed a CSPRNG, from which the ephemeral key
is derived.
Fixes#9452
--
This is a minimalist (in terms of patch size) solution, though
not the most parsimonious in its use of primitives:
- csprng_key = ChopMD-256(SHA2-512(priv.D||entropy||hash))
- reader = AES-256-CTR(k=csprng_key)
This, however, provides at most 128-bit collision-resistance,
so that Adv will have a term related to the number of messages
signed that is significantly worse than plain ECDSA. This does
not seem to be of any practical importance.
ChopMD-256(SHA2-512(x)) is used, rather than SHA2-256(x), for
two sets of reasons:
*Practical:* SHA2-512 has a larger state and 16 more rounds; it
is likely non-generically stronger than SHA2-256. And, AFAIK,
cryptanalysis backs this up. (E.g., [Biryukov] gives a
distinguisher on 47-round SHA2-256 with cost < 2^85.) This is
well below a reasonable security-strength target.
*Theoretical:* [Coron] and [Chang] show that Chop-MD(F(x)) is
indifferentiable from a random oracle for slightly beyond the
birthday barrier. It seems likely that this makes a generic
security proof that this construction remains UF-CMA is
possible in the indifferentiability framework.
--
Many thanks to Payman Mohassel for reviewing this construction;
any mistakes are mine, however. And, as he notes, reusing the
private key in this way means that the generic-group (non-RO)
proof of ECDSA's security given in [Brown] no longer directly
applies.
--
[Brown]: http://www.cacr.math.uwaterloo.ca/techreports/2000/corr2000-54.ps
"Brown. The exact security of ECDSA. 2000"
[Coron]: https://www.cs.nyu.edu/~puniya/papers/merkle.pdf
"Coron et al. Merkle-Damgard revisited. 2005"
[Chang]: https://www.iacr.org/archive/fse2008/50860436/50860436.pdf
"Chang and Nandi. Improved indifferentiability security analysis
of chopMD hash function. 2008"
[Biryukov]: http://www.iacr.org/archive/asiacrypt2011/70730269/70730269.pdf
"Biryukov et al. Second-order differential collisions for reduced
SHA-256. 2011"
[Nguyen]: ftp://ftp.di.ens.fr/pub/users/pnguyen/PubECDSA.ps
"Nguyen and Shparlinski. The insecurity of the elliptic curve
digital signature algorithm with partially known nonces. 2003"
New tests:
TestNonceSafety: Check that signatures are safe even with a
broken entropy source.
TestINDCCA: Check that signatures remain non-deterministic
with a functional entropy source.
Updated "golden" KATs in crypto/tls/testdata that use ECDSA suites.
Change-Id: I55337a2fbec2e42a36ce719bd2184793682d678a
Reviewed-on: https://go-review.googlesource.com/3340
Reviewed-by: Adam Langley <agl@golang.org>
A new attack on CBC padding in SSLv3 was released yesterday[1]. Go only
supports SSLv3 as a server, not as a client. An easy fix is to change
the default minimum version to TLS 1.0 but that seems a little much
this late in the 1.4 process as it may break some things.
Thus this patch adds server support for TLS_FALLBACK_SCSV[2] -- a
mechanism for solving the fallback problem overall. Chrome has
implemented this since February and Google has urged others to do so in
light of yesterday's news.
With this change, clients can indicate that they are doing a fallback
connection and Go servers will be able to correctly reject them.
[1] http://googleonlinesecurity.blogspot.com/2014/10/this-poodle-bites-exploiting-ssl-30.html
[2] https://tools.ietf.org/html/draft-ietf-tls-downgrade-scsv-00
LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/157090043
Currently an ECDHE handshake uses the client's curve preference. This
generally means that we use P-521. However, P-521's strength is
mismatched with the rest of the cipher suite in most cases and we have
a fast, constant-time implementation of P-256.
With this change, Go servers will use P-256 where the client supports
it although that can be overridden in the Config.
LGTM=bradfitz
R=bradfitz
CC=golang-codereviews
https://golang.org/cl/66060043
The renegotiation extension was introduced[1] due to an attack by Ray in
which a client's handshake was spliced into a connection that was
renegotiating, thus giving an attacker the ability to inject an
arbitary prefix into the connection.
Go has never supported renegotiation as a server and so this attack
doesn't apply. As a client, it's possible that at some point in the
future the population of servers will be sufficiently updated that
it'll be possible to reject connections where the server hasn't
demonstrated that it has been updated to address this problem.
We're not at that point yet, but it's good for Go servers to support
the extension so that it might be possible to do in the future.
[1] https://tools.ietf.org/search/rfc5746
R=golang-codereviews, mikioh.mikioh
CC=golang-codereviews
https://golang.org/cl/48580043
The practice of storing reference connections for testing has worked
reasonably well, but the large blocks of literal data in the .go files
is ugly and updating the tests is a real problem because their number
has grown.
This CL changes the way that reference tests work. It's now possible to
automatically update the tests and the test data is now stored in
testdata/. This should make it easier to implement changes that affect
all connections, like implementing the renegotiation extension.
R=golang-codereviews, r
CC=golang-codereviews
https://golang.org/cl/42060044
