Simple encryption service Goodie

**What does your Instant Answer do?**
Provides a simple crypto service to encrypt and decrypt a string using the RC4 algorithm.

**What problem does your Instant Answer solve (Why is it better than organic links)?**
Provides way to pass sensitive info from one user to another just using their browser and a preshared key.

**What are some example queries that trigger this Instant Answer?**

crypt encrypt key string
crypt decrypt key string
crypt en key string
crypt de key string

**Which communities will this Instant Answer be especially useful for? (gamers, book lovers, etc)**
Mostly sysadmins and people that need to pass sensitive information around, like passwords or credit card numbers.

**Is this Instant Answer connected to a DuckDuckHack [Instant Answer idea](https://duck.co/ideas)?**
Yes, https://duck.co/ideas/idea/1463/simple-encryption-service

**Which existing Instant Answers will this one supercede/overlap with?**
None that I know.

**Are you having any problems? Do you need our help with anything?**
Not so far, maybe after more testing problems can arise :)

**Where did you hear about DuckDuckHack? (For first time contributors)**
On the news, about 2 years ago.

**What does the Instant Answer look like? (Provide a screenshot for new or updated Instant Answers)**

![screen shot 2014-11-26 at 6 51 29 p m]
(https://cloud.githubusercontent.com/assets/4934646/5210590/b5b3c5b4-759d-11e4-9166-4c49932f5adf.png)



## Checklist
Please place an 'X' where appropriate.

```
[X] Added metadata and attribution information (https://duck.co/duckduckhack/metadata)
[X] Wrote test file and added to t/ directory (https://duck.co/duckduckhack/goodie_tests)
[X] Verified that instant answer adheres to design guidelines (https://duck.co/duckduckhack/design_styleguide)
[X] Verified that instant answer adheres to code styleguide (https://duck.co/duckduckhack/code_styleguide)
[X] Tested cross-browser compatibility

    Please let us know which browsers/devices you've tested on:
    - Windows 8
        [] Google Chrome
        [] Firefox
        [] Opera
        [] IE 10

    - Windows 7
        [] Google Chrome
        [] Firefox
        [] Opera
        [] IE 8
        [] IE 9
        [] IE 10

    - Windows XP
        [] IE 7
        [] IE 8

    - Mac OSX
        [X] Google Chrome
        [X] Firefox
        [] Opera
        [X] Safari

    - iOS (iPhone)
        [] Safari Mobile
        [] Google Chrome
        [] Opera

    - iOS (iPad)
        [] Safari Mobile
        [] Google Chrome
        [] Opera

    - Android
        [X] Firefox
        [X] Native Browser
        [X] Google Chrome
        [] Opera
Please remove these extra lines too