Crypto refactor

[johningve]

This is a complete rewrite of the crypto implementations based on discussion in #34.

Important Changes:

• The CryptoImpl interface is replaced with the CryptoBase interface which is much simpler:

  // CryptoBase provides the basic cryptographic methods needed to create, verify, and combine signatures.
  type CryptoBase interface {
  // Sign creates a cryptographic signature of the given message.
  Sign(message []byte) (signature QuorumSignature, err error)
  // Combine combines multiple signatures into a single signature.
  Combine(signatures ...QuorumSignature) (signature QuorumSignature, err error)
  // Verify verifies the given quorum signature against the message.
  Verify(signature QuorumSignature, message []byte) bool
  // BatchVerify verifies the given quorum signature against the batch of messages.
  BatchVerify(signature QuorumSignature, batch map[hotstuff.ID][]byte) bool
  }

• The ThresholdSignature interface is renamed to QuorumSignature, and the Signature interface is removed.
• ConnectionMetadata allows for metadata to be sent to other replicas.
• This metadata is used by the bls12 package to send a proof-of-possession to all replicas.

[codecov-commenter]

Codecov Report

Merging #36 (e21bf85) into master (25e7ec2) will increase coverage by 5.56%. The diff coverage is 79.68%.

@@            Coverage Diff             @@
##           master      #36      +/-   ##
==========================================
+ Coverage   53.31%   58.87%   +5.56%     
==========================================
  Files          70       70              
  Lines        6398     6410      +12     
==========================================
+ Hits         3411     3774     +363     
+ Misses       2710     2347     -363     
- Partials      277      289      +12     

Flag	Coverage Δ
unittests	58.87% <79.68%> (+5.56%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
crypto/bls12/bls12.go	64.12% <69.94%> (+15.02%)	:arrow_up:
crypto/crypto.go	70.75% <70.75%> (ø)
crypto/ecdsa/ecdsa.go	72.91% <71.25%> (+13.02%)	:arrow_up:
backend/config.go	81.03% <76.56%> (+17.03%)	:arrow_up:
twins/network.go	91.20% <90.56%> (+5.41%)	:arrow_up:
crypto/cache.go	88.42% <97.95%> (+18.88%)	:arrow_up:
backend/server.go	61.68% <100.00%> (+15.38%)	:arrow_up:
consensus/consensus.go	73.05% <100.00%> (+9.58%)	:arrow_up:
consensus/events.go	100.00% <100.00%> (ø)
consensus/modules.go	100.00% <100.00%> (+6.45%)	:arrow_up:
... and 32 more

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[johningve]

@meling There are some changes to various tests because I had to change the testutil.TestModules function and make the testutil.CreateBuilders use the twins network to get the new metadata working. It's kinda ugly now, but I'll probably revisit it at some point and try to clean it up.

[meling]

We should make some progress towards getting this merged. What remains to be discussed and what remains to be implemented?

[johningve]

@meling I split the Verify function into two: Verify and BatchVerify. I think this is more sensible than the approach of using the VerifyOption stuff. These functions are no longer responsible for checking whether the number of signatures constitutes a quorum, I moved that to the higher-level Crypto module's functions.