I am getting confused with what exactly is the nature of the Signed Prekey (SPK) used in signal protocol. I understand what it is used for, but I think the confusion stems from its name. Is it just the normal key-pair whose public part will get signed and sent to the server as a part of the "key bundle"?
Which means, THAT exact SPK that we send in the bundle as well is just a random public key, and is in no way signed or modified by the IdentityKey itself.
Based on my understanding, this SPK could also be named "Key that WILL get signed but IS NOT signed" Or is there a previous key, lets call it just "PreKey" that gets signed by IdentityKey and thats how we get Signed PreKey?
I sound like a crazy person to myself and it's really hard to even formulate this question. I've read technical paper on signal's website and also whitepapers of signal implementation in WhatsApp but still I'm getting confused how is this SPK obtained?
Hope this doesn't look like non-sense. Thanks