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.
ec0a7b3 Don't touch leading zeros in wnaf_fixed. (Jonas Nick)
9e36d1b Fix bug in wnaf_fixed where the wnaf array is not completely zeroed when given a 0 scalar. (Jonas Nick)
96f68a0 Don't invert scalar in wnaf_fixed when it is even because a caller might intentionally give a scalar with many leading zeros. (Jonas Nick)
6dbb007 Increase sparsity of pippenger fixed window naf representation (Jonas Nick)
Pull request description:
Fixes#506
Tree-SHA512: 49a237a7d09c0c376ba4e6b1f522b9aff2517e420dfef9df810fd5ba920e0b98be8fe3f730b32e41b4aef475bc4cf3b13220024bd8d6f40c2744e6f392ff97a8
82a96e4 tests: Make sure we get the requested number of bytes from /dev/urandom (practicalswift)
Pull request description:
Make sure we get the requested number of bytes from `/dev/urandom`.
Tree-SHA512: 1b035942fd2a6ee2423fb2a2a0a0f294682c51434f86e5c106fb493d77f45aa8070662190aca6441fe389b8cdcc132d432517b8e826be2ac530a1511cd0c8919
The only reason OpenSSL 1.1 was not supported was the removal of direct
access to r and s in ECDSA_SIG. This commit adds a simplified version of
ECDSA_SIG_get0 for < 1.1 that can be used like ECDSA_SIG_get0 in >= 1.1
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
7a78f60 Print whether we're building benchmarks (Pieter Wuille)
4afec9f Build benchmarks by default (Pieter Wuille)
Pull request description:
Building benchmarks is fast, and I have on more than one occasion forgotten to pass `--enable-benchmark`, resulting in accidentally benchmarking a former build.
Build them by default.
Tree-SHA512: ce9096e42d9c19b63644f6b7ae153e92f9a37c3727f380329dfa332ce22a5e43151f1525979bd3516dd12f568e5e389b0acda2c383fca0e80c3cadc1d9b1d55a
