| commit | 12d9ed670da3edd64ce8175cfe0e091982989c18 | [log] [tgz] |
|---|---|---|
| author | David Benjamin <davidben@google.com> | Fri Jun 14 17:06:52 2019 -0400 |
| committer | Adam Langley <agl@google.com> | Wed Jun 19 17:19:04 2019 +0000 |
| tree | 57bb48f000fd501a044e7f92484287fc5a517747 | |
| parent | cef9d3f38d72f13412c79157c25753e22cb05f7e [diff] |
Avoid leaking intermediate states in point doubling special case. Point addition formulas for short Weierstrass curves are often incomplete and do not work for P + P. EC implementations usually rely on constant-time operations never hitting this case, or at least it being rare[0]. However, the condition checks several values. Our C functions use && and ||, and the P-256 assembly also branches. This can leak intermediate values via a small side channel. Thanks to David Schrammel and Samuel Weiser for reporting this. nistz256 base point multiplication (keygen, ECDSA signing) is unaffected due to ecp_nistz256_point_add_affine lacking a doubling case. nistp224 and nistp256 base point multiplication, on some compilers, are saved by quirks of the "mixed" path. The generic code's base point multiplication and all methods' arbitrary point multiplication (ECDH; ephemeral keys makes this less interesting) are affected. Fix the branches in the nistz256 assembly, and use bit operations in C. Note the C versions are all different because P-224 believes true is 1, P-256 believes true is any non-zero value, and the generic code believes true is 0xf...f. This should be double-checked when reviewing. Aside: The nistz256 assembly also special-cases nontrivial P + (-P) in arbitrary point multiplication. Fortunately, the formulas in util.c hold there and I believe one can show P + (-P) is unreachable for all curves. Still, it would be nice to omit the branch if we can verify the assembly works anyway. [0] https://github.com/openssl/openssl/blob/03da376ff7504c63a1d00d57cf41bd7b7e93ff65/crypto/ec/ecp_nistp521.c#L1259 Change-Id: I8958624cd6b5272e5076c6c1605ab089e85f4cb7 Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/36465 Reviewed-by: Adam Langley <agl@google.com> Commit-Queue: Adam Langley <agl@google.com>
BoringSSL is a fork of OpenSSL that is designed to meet Google's needs.
Although BoringSSL is an open source project, it is not intended for general use, as OpenSSL is. We don't recommend that third parties depend upon it. Doing so is likely to be frustrating because there are no guarantees of API or ABI stability.
Programs ship their own copies of BoringSSL when they use it and we update everything as needed when deciding to make API changes. This allows us to mostly avoid compromises in the name of compatibility. It works for us, but it may not work for you.
BoringSSL arose because Google used OpenSSL for many years in various ways and, over time, built up a large number of patches that were maintained while tracking upstream OpenSSL. As Google's product portfolio became more complex, more copies of OpenSSL sprung up and the effort involved in maintaining all these patches in multiple places was growing steadily.
Currently BoringSSL is the SSL library in Chrome/Chromium, Android (but it's not part of the NDK) and a number of other apps/programs.
There are other files in this directory which might be helpful: