We should be careful about stringifying here. If it's significant on both ends, why not get rid of it?

````js
sjcl.hash.sha256.hash({ foo: 'bar' })
[-1956978631, -251501254, 1237199275, 371573479, 2056813515, -1386188451, -367756938, 946769831]
sjcl.hash.sha256.hash(JSON.stringify({ foo: 'bar' }))
[2050539393, -209455468, 867004048, 221623266, 945132535, 1786477237, -734700661, -1541479861]
````