8bc6aeffa9a191e677cb9e3a22fff130f16990f3 Add SHA256 selftest (Pieter Wuille)
5e5fb28b4a45d7e35e55b5f5feead2be07bccc28 Use additional system macros to figure out endianness (Pieter Wuille)
Pull request description:
These are all the architecture macros I could find with known endianness. Use those as a fallback when __BYTE_ORDER__ isn't available.
See https://github.com/bitcoin-core/secp256k1/pull/787#issuecomment-673764652
It also adds a SHA256 selftest, so that improperly overriding the endianness detection will be detected at runtime.
ACKs for top commit:
real-or-random:
ACK 8bc6aeffa9a191e677cb9e3a22fff130f16990f3 I read the diff, and tested that the self-test passes/fails with/without the correct endianness setting
gmaxwell:
ACK 8bc6aeffa9a191e677cb9e3a22fff130f16990f3 looks good and I also ran the tests on MIPS-BE and verified that forcing it to LE makes the runtime test fail.
Tree-SHA512: aca4cebcd0715dcf5b58f5763cb4283af238987f43bd83a650e38e127f348131692b2eed7ae5b2ae96046d9b971fc77c6ab44467689399fe470a605c3458ecc5
This commit adds three new cryptosystems to libsecp256k1:
Pedersen commitments are a system for making blinded commitments
to a value. Functionally they work like:
commit_b,v = H(blind_b || value_v),
except they are additively homorphic, e.g.
C(b1, v1) - C(b2, v2) = C(b1 - b2, v1 - v2) and
C(b1, v1) - C(b1, v1) = 0, etc.
The commitments themselves are EC points, serialized as 33 bytes.
In addition to the commit function this implementation includes
utility functions for verifying that a set of commitments sums
to zero, and for picking blinding factors that sum to zero.
If the blinding factors are uniformly random, pedersen commitments
have information theoretic privacy.
Borromean ring signatures are a novel efficient ring signature
construction for AND/OR admissions policies (the code here implements
an AND of ORs, each of any size). This construction requires
32 bytes of signature per pubkey used plus 32 bytes of constant
overhead. With these you can construct signatures like "Given pubkeys
A B C D E F G, the signer knows the discrete logs
satisifying (A || B) & (C || D || E) & (F || G)".
ZK range proofs allow someone to prove a pedersen commitment is in
a particular range (e.g. [0..2^64)) without revealing the specific
value. The construction here is based on the above borromean
ring signature and uses a radix-4 encoding and other optimizations
to maximize efficiency. It also supports encoding proofs with a
non-private base-10 exponent and minimum-value to allow trading
off secrecy for size and speed (or just avoiding wasting space
keeping data private that was already public due to external
constraints).
A proof for a 32-bit mantissa takes 2564 bytes, but 2048 bytes of
this can be used to communicate a private message to a receiver
who shares a secret random seed with the prover.
Also: get rid of precomputed H tables (Pieter Wuille)
ECDSA signing has a retry loop for the exceptionally unlikely case
that S==0. S is not a secret at this point and this case is so
rare that it will never be observed but branching on it will trip
up tools analysing if the code is constant time with respect to
secrets.
Derandomized ECDSA can also loop on k being zero or overflowing,
and while k is a secret these cases are too rare (1:2^255) to
ever observe and are also of no concern.
This adds a function for marking memory as no-longer-secret and
sets it up for use with the valgrind memcheck constant-time
test.
There were several places where the code was non-constant time
for invalid secret inputs. These are harmless under sane use
but get in the way of automatic const-time validation.
(Nonce overflow in signing is not addressed, nor is s==0 in
signing)
cd473e0 Avoid calling secp256k1_*_is_zero when secp256k1_*_set_b32 fails. (Gregory Maxwell)
Pull request description:
Most of the codebase correctly used short-cutting to avoid calling
_is_zero on possibly incompletely initialized elements, but a few
places were missed.
ACKs for commit cd473e:
sipa:
utACK cd473e02c372217c3a6608ce5afaa543ed78f891
jonasnick:
utACK cd473e02c372217c3a6608ce5afaa543ed78f891
Tree-SHA512: d6af2863f6795d2df26f2bd05a4e33085e88c45f7794601ea57e67238a2073ef1ee3ba0feab62a7fcbc0636c48dfd80eea07d0ca4f194414127f914b0478c732
Most of the codebase correctly used short-cutting to avoid calling
_is_zero on possibly incompletely initialized elements, but a few
places were missed.
Before this commit secp256k1_context_randomize called illegal_callback
when called on a context not initialized for signing. This is not
documented. Moreover, it is not desirable because non-signing contexts
may use randomization in the future.
This commit makes secp256k1_context_randomize a noop in this case. This
is safe because the context cannot be used for signing anyway.
This fixes#573 and it fixesrust-bitcoin/rust-secp256k1#82.
c7680e5 Reduce usage of hardcoded size constants (Thomas Snider)
Pull request description:
In particular the usage of keylen in nonce_function_rfc6979 seemed precarious - in one conditional it was unconditionally set, then in the next it was added to. While it was clearly correct as written, I think this change makes it easier to reason about for new eyes and more resistant to breakage if there is any future change to what gets fed into the PRNG.
Tree-SHA512: 2241c183acc0f318f85a11ccff7fe28de7777bc53dea93ab8308bad15871047a268c6a2b36f77a599dce536fca48ab305ea746223840bc10953c893daffa0a50
Make sure we clear the nonce data even if the nonce function fails (it may have written partial data), and call memset only once in the case we iterate to produce a valid signature.
The `ARG_CHECK` macro requires that a variable called `ctx` exist and be
non-NULL. However, in several functions that do not use the context variable,
we simply ignore it with `(void)ctx`. Replace these with explicit checks for
non-NULLness to avoid invalid memory accesses.
Squashed and rebased. Thanks to @theuni and @faizkhan00 for doing
the majority of work here! Also thanks to @btchip for help with debugging
and review.
