C secp256k1 : what is the purpose of secp256k1_context_randomize?
I just merged a PR by Rusty Russell that aims to explain its purpose. From the text that was added:


  While secp256k1 code is written to be constant-time no matter what secret values are, it's possible that a future compiler may output code which isn't, and also that the CPU may not emit the same radio frequencies or draw the same amount power for all values.
  
  This function provides a seed which is combined into the blinding value: that blinding value is added before each multiplication (and removed afterwards) so that it does not affect function results, but shields against attacks which rely on any input-dependent behaviour.
  
  You should call this after secp256k1_context_create or secp256k1_context_clone, and may call this repeatedly afterwards.