incremental_hmac

The standard library's HMAC implementation is rather limited in that it can only work on data that has a to_slice method defined. This works fine for the typical web use cases for strings and byte buffers but does not scale well to calculating the HMAC of large files which are inconvenient to fit in memory.

This shard monkey patches OpenSSL::HMAC and adds an incremental interface modeled on Ruby's OpenSSL::HMAC class. It does this by calling into the same LibCrypto wrapper that the standard library does and should be "fairly safe" but I wouldn't advise it for production use at this time.

Installation

1. Add the dependency to your shard.yml:

   dependencies:
     incremental_hmac:
       github: tlrasor/incremental_hmac
   

2. Run shards install

Usage

require "incremental_hmac"
## The incremental interface is an instance of HMAC
hmac = OpenSSL::HMAC.new(algorithm, key)
# get an IO/something that produces slices
File.open(path, "r") do |io|
  data_slice = Bytes.new(8192)
  loop do
    read = io.read(data_slice)
    break if read < 1
    ## Here we update the hmac with the current buffer
    hmac << data_slice[0, read]
  end
end
## Now just call digest or hexdigest to finalize
hmac.digest

Note, currently, HMAC digests can currently only be called once because the structure is finalized. This is somewhat a consequence of the backing C library and some thought needs to be put into how to solve this.

Helpers

There are also some class method helpers which can handle reading the data in from a file

key = "<some secret hmac key>"
path = Path["<some file path string>"]
digest = OpenSSL::HMAC.hexdigest(OpenSSL::Algorithm::SHA256, key, path)

Development

Do some dev and write some tests plz

Contributing

1. Fork it (https://github.com/tlrasor/incremental_hmac/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• Travis Rasor - creator and maintainer