Use ES2015 classes

ES2015 classes are both clearer and more familiar to users of other languages than the ES5 equivalents.
Also let and const are used in preference to var.

Author: chrisveness

Diff for: README.md

@@ -1,13 +1,18 @@
 crypto
 ======
 
-Libraries of cryptographic functions implemented in JavaScript.
+Reference implementations of AES & SHA cryptographic functions in JavaScript.
+
+These annotated implementations follow the standards very closely, in order to assist in studying 
+the standards and underlying algorithms. Note for production use I would recommend the
+[Web Cryptography API](https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto) for the browser, 
+or the [crypto](https://nodejs.org/api/crypto.html) library in Node.js.
 
 aes.js
 ------
 
-This is a reference implementation of the algorithm described in the FIPS-197 standard. It implements
-the standard very closely, in order to aid in understanding the standard and the algorithm itself.
+This is a reference implementation of the AES (Rijndael cipher) algorithm described in the FIPS-197 
+standard.
 
 This comprises:
 
@@ -35,8 +40,7 @@ More details are available at www.movable-type.co.uk/scripts/aes.html.
 sha1.js
 -------
 
-This is a reference implementation of the algorithm described in the FIPS-180-4 standard. It implements
-the standard very closely, in order to aid in understanding the standard and the algorithm itself.
+This is a reference implementation of the SHA-1 algorithm described in the FIPS-180-4 standard.
 
 This comprises:
 
@@ -47,8 +51,7 @@ More details are available at www.movable-type.co.uk/scripts/sha1.html.
 sha256.js
 ---------
 
-This is a reference implementation of the algorithm described in the FIPS-180-4 standard. It implements
-the standard very closely, in order to aid in understanding the standard and the algorithm itself.
+This is a reference implementation of the SHA-256 algorithm described in the FIPS-180-4 standard.
 
 This comprises:
 
@@ -62,8 +65,7 @@ More details are available at www.movable-type.co.uk/scripts/sha256.html.
 sha512.js
 ---------
 
-This is a reference implementation of the algorithm described in the FIPS-180-4 standard. It implements
-the standard very closely, in order to aid in understanding the standard and the algorithm itself.
+This is a reference implementation of the SHA-512 algorithm described in the FIPS-180-4 standard.
 
 This comprises:
 
@@ -77,8 +79,7 @@ More details are available at www.movable-type.co.uk/scripts/sha512.html.
 sha3.js
 -------
 
-This is a reference implementation of the algorithm described in the FIPS-202 standard. It implements
-the standard very closely, in order to aid in understanding the standard and the algorithm itself.
+This is a reference implementation of the SHA-3 (Keccak) algorithm described in the FIPS-202 standard.
 
 This comprises:
 
@@ -111,9 +112,17 @@ Documentation
 
 Documentation for all these methods is available at www.movable-type.co.uk/scripts/js/crypto/docs.
 
-Browser support
----------------
+JavaScript
+----------
 
-IE9- doesn’t have btoa()/atob(): if you need to support IE9- 
-([no!](https://www.microsoft.com/en-gb/WindowsForBusiness/End-of-IE-support)), you can use David 
-Chambers’ [Base64 polyfill](https://github.com/davidchambers/Base64.js).
+Cryptographically-speaking, browsers are 
+[inherently](//www.nccgroup.trust/us/about-us/newsroom-and-events/blog/2011/august/javascript-cryptography-considered-harmful)
+[insecure](//tonyarcieri.com/whats-wrong-with-webcrypto) (Node.js does not suffer the same problems),
+but these implementations are intended for study rather than production use. With its untyped C-style 
+syntax, JavaScript reads remarkably close to pseudo-code: exposing the algorithms with a minimum of 
+syntactic distractions.
+
+These implementations are written in ES2015 version of JavaScript; ES2015 `class`es are both clearer
+and more familiar to users of other languages than the ES5 equivalents, and `let` and `const` are
+good practice and communicate intent better than `var`. Other idiomatic JavaScript which might be 
+less familiar to users of other languages has generally been avoided.