I need to generate a hash on each uploaded file. The hash must be identical to hash git generated for a given file (which is, in a layman term, a variant of sha1).

I looked into `/nodejs-v0.10.22-src/core-modules-sources/lib/crypto.js`. The library refers to native binding. For portability, I do not want to depends on native code.

Is there a way to add a custom crypto algorithm into nodejs crypto module, in JavaScript, such that I can do these:

```
var hash = crypto.createHash('githash');
hash.update('...');

```