This change moves test data into the binaries rather than reading them from
the disk at runtime.
Advantages:
- Tests become distributable
- Cross-compile friendly. Build on one machine and execute in an arbitrary
location on another.
- Easier testing for backports. Users can verify that tests pass without having
to track down corresponding test data.
- More trustworthy test results and easier quality assurance as tests make
fewer assumptions about their environment.
- Tests could theoretically run at client/daemon startup and exit on failure.
Disadvantages:
- Required 'hexdump' build-dependency. This is a standard bsd tool that should
be usable everywhere. It is likely already installed on all build-machines.
- Tests can no longer be fudged after build by altering test-data.
To fix a minor malleability found by Sergio Lerner (reported here:
https://bitcointalk.org/index.php?topic=8392.msg1245898#msg1245898)
The problem is that if (R,S) is a valid ECDSA signature for a given
message and public key, (R,-S) is also valid. Modulo N (the order
of the secp256k1 curve), this means that both (R,S) and (R,N-S) are
valid. Given that N is odd, S and N-S have a different lowest bit.
We solve the problem by forcing signatures to have an even S value,
excluding one of the alternatives.
This commit just changes the signing code to always produce even S
values, and adds a verification mode to check it. This code is not
enabled anywhere yet. Existing tests in key_tests.cpp verify that
the produced signatures are still valid.
