First off, thanks for the interest, bud! Open source thrives off collaboration.
Basically, either find an issue or open one. Describe what it is you are going to do, so that you can get feedback. Then, fork that shit and go ham!
Please make sure that your code passes the test cases, and if you're adding features, that there are new tests to go with them. And make sure that your code passes tslint.
Other than that, just write some sweet crypto code and we'll be in business.