Automatic public project deploy for instance on AWS

Question:

I would like to know how I can configure Travis CI to automatically deploy a public project from GitHub after running the build and all tests pass.

I have noticed this configuration of the .travis.yml file, but the question that remains, informing the access_key_id and secret_access_key attributes is really safe, how could you configure GitHub to automatically deploy public projects?

/#http://docs.travis-ci.com/user/deployment/s3/
deploy:
  provider: s3
  access_key_id: "" #YOUR ENCRYPTED AWS ACCESS KEY
  secret_access_key: "" #YOUR ENCRYPTED AWS SECRET KEY
  bucket: "make.stanleygeorge.com"
  skip_cleanup: true
  local-dir: out
on:
  tags: true

References:

Setup Travis-CI for continuous integration

S3 Deployment

AWS CodeDeploy