John from Braintree here. In the case of our client-side encryption library we use sjcl (http://crypto.stanford.edu/sjcl/ http://crypto.stanford.edu/sjcl/) to g

John from Braintree here. In the case of our client-side encryption library we use sjcl (http://crypto.stanford.edu/sjcl/ http://crypto.stanford.edu/sjcl/) to generate the symmetric keys for encryption. This library uses Ferguson and Schneier's Fortuna PRNG to generate random values. The main entropy source is crypto.getRandomValues (https://developer.mozilla.org/en-US/docs/DOM/window.crypto.getRandomValues https://developer.mozilla.org/en-US/docs/DOM/window.crypto.g...) where it is available. In other places it uses mouse movements to provide entropy for the PRNG.