The Window.crypto read-only property returns the Crypto object associated to the global object. This object allows web pages access to certain cryptographic related services.
The SubtleCrypto interface represents a set of cryptographic primitives. It is available via the Crypto.subtle properties available in a window context (via Window.crypto).
Wrote a little sample script to hash, generate a symmetric key and en/decrypt data. It's also possible to sign (using HMAC) data, generate and use asymmetric (private/public) keys and so on.