Implementation of scalable collective signing

Current version

cosi requires the following formula to be installed:
go 1.9 Open source programming language to build simple/reliable/efficient software

Formula history

Mike McQuaid Use hash rockets again. (#5177)
Mike McQuaid Use Ruby 1.9+ symbol hash keys in all formulae. (#4942)
Zhiming Wang cosi: update go_resource indentation style
ilovezfs cosi: fix the test
Nicolas GAILLY cosi 0.8.5 (new formula)