Add docs for Crypto

docs/Crypto.md

@@ -1 +1,36 @@
 # Crypto
+
+The cryptographic primitives (ECDSA and HMAC) implementations in this package
+have been audited by:
+
+* The BitPay engineering team
+
+## random
+
+The `bitcore.Crypto.Random` namespace contains a single function, named
+`getRandomBuffer(size)` that returns a `Buffer` instance with random bytes. It
+may not work depending on the engine that bitcore is running on (doesn't work
+with IE versions lesser than 11).
+
+## bn
+
+The `bitcore.Crypto.BN` class contains a wrapper around
+[bn.js](https://github.com/indutny/bn.js), the bignum library used internally
+in bitcore.
+
+## point
+
+The `bitcore.Crypto.Point` class contains a wrapper around the class Point of
+[elliptic.js](https://github.com/indutny/elliptic.js), the elliptic curve
+library used internally in bitcore.
+
+## hash
+
+The `bitcore.Crypto.Hash` namespace contains a set of hashes and utilities.
+These are either the native `crypto` hash functions from `node.js` or their
+respective browser shims as provided by the `browserify` library.
+
+## ecdsa
+
+`bitcore.Crypto.ECDSA` contains a pure javascript implementation of the
+elliptic curve DSA signature scheme.