$ gem install travis
Fetching travis-1.8.11.gem
Successfully installed travis-1.8.11
1 gem installed
$ echo "bar" > food
$ travis encrypt-file food
encrypting food for travis-ci/travis.rb
storing result as food.enc
storing secure env variables for decryption
wrong number of arguments (given 1, expected 2)
for a full error report, run travis report --pro
$ travis report --pro
System
Ruby:                     Ruby 2.3.4-p301
Operating System:         Mac OS X 10.15.3
RubyGems:                 RubyGems 3.0.3

CLI
Version:                  1.8.11
Plugins:                  none
Auto-Completion:          yes
Last Version Check:       2020-03-04 15:06:09 -0500

Session
API Endpoint:             https://api.travis-ci.com/
Logged In:                as "BanzaiMan"
Verify SSL:               yes
Enterprise:               no

Endpoints
org:                      https://api.travis-ci.org/ (access token)
com:                      https://api.travis-ci.com/ (access token, current)
staging-com:              https://api-staging.travis-ci.com/ (access token)
staging-org:              https://api-staging.travis-ci.org/ (access token)

Last Exception
An error occurred running `travis encrypt-file --pro`:
    ArgumentError: wrong number of arguments (given 1, expected 2)
        from /Users/asari/.rbenv/versions/2.3.4/lib/ruby/gems/2.3.0/gems/travis-1.8.11/lib/travis/cli/encrypt_file.rb:79:in `env_name'
        from /Users/asari/.rbenv/versions/2.3.4/lib/ruby/gems/2.3.0/gems/travis-1.8.11/lib/travis/cli/encrypt_file.rb:70:in `decrypt_command'
        from /Users/asari/.rbenv/versions/2.3.4/lib/ruby/gems/2.3.0/gems/travis-1.8.11/lib/travis/cli/encrypt_file.rb:42:in `run'
        from /Users/asari/.rbenv/versions/2.3.4/lib/ruby/gems/2.3.0/gems/travis-1.8.11/lib/travis/cli/command.rb:198:in `execute'
        from /Users/asari/.rbenv/versions/2.3.4/lib/ruby/gems/2.3.0/gems/travis-1.8.11/lib/travis/cli.rb:64:in `run'
        from /Users/asari/.rbenv/versions/2.3.4/lib/ruby/gems/2.3.0/gems/travis-1.8.11/bin/travis:18:in `<top (required)>'
        from /Users/asari/.rbenv/versions/2.3.4/bin/travis:23:in `load'
        from /Users/asari/.rbenv/versions/2.3.4/bin/travis:23:in `<main>'


For issues with the command line tool, please visit https://github.com/travis-ci/travis.rb/issues.
For Travis CI in general, go to https://github.com/travis-ci/travis-ci/issues or email support@travis-ci.com.
$ pwd
/Users/asari/Development/src/travis-ci/travis.rb
$ gem build travis.gemspec
WARNING:  open-ended dependency on backports (>= 0) is not recommended
  use a bounded requirement, such as '~> x.y'
WARNING:  open-ended dependency on rspec-its (>= 0, development) is not recommended
  use a bounded requirement, such as '~> x.y'
WARNING:  See http://guides.rubygems.org/specification-reference/ for help
  Successfully built RubyGem
  Name: travis
  Version: 1.8.11
  File: travis-1.8.11.gem
$ gem install ./travis-1.8.11.gem
Successfully installed travis-
8000
1.8.11
1 gem installed
$ travis encrypt-file food
encrypting food for travis-ci/travis.rb
storing result as food.enc
DANGER ZONE: Override existing food.enc? |no| yes
storing secure env variables for decryption

Please add the following to your build script (before_install stage in your .travis.yml, for instance):

    openssl aes-256-cbc -K $encrypted_39ccb32d95ed_key -iv $encrypted_39ccb32d95ed_iv -in food.enc -out food -d

Pro Tip: You can add it automatically by running with --add.

Make sure to add food.enc to the git repository.
Make sure not to add food to the git repository.
Commit all changes to your .travis.yml.