types: Expected Buffer, length to follow

src/types.js

@@ -3,7 +3,7 @@ var ecurve = require('ecurve')
 var typeforce = require('typeforce')
 
 function nBuffer (value, n) {
-  if (!Buffer.isBuffer(value)) return false
+  typeforce(types.Buffer, value)
   if (value.length !== n) throw new Error('Expected ' + (n * 8) + '-bit Buffer, got ' + (value.length * 8) + '-bit Buffer')
   return true
 }