Assuming you're talking about ECDSA signing. For BIP340/Schnorr signatures, see this answer.
For valid signatures
d: the private key
P=d*G: the public key
k1: the (first) nonce
R1=k1*G: the public first nonce
r1=R1.x mod n: the public first nonce as it will be encoded in the signature.
k2=2*k1, R2=k2*G=2*R1, r2=R2.x mod n: the same for the second nonce
How do you make a secure wallet?
Security depends on lot of things including user and not just the wallets. Most of the open source Bitcoin wallets with active development are secure.
If you wanted to secretly get bitcoin from someone, how do you get it?
Share your address privately and ask them to send bitcoin. Follow best practices:
How do you get the ...
I believe "anonymously" is a better fit than "secretly". Since every transaction is public and you can't hide the transfer of coins. What you can hide is the identity of the parties involved.
As for creating a wallet, you can run your own node, possibly having a hardware wallet (not strictly necessary but it helps).
As for getting the ...
Easy. People are weak and easy to scare, so just a new law that says huge fine and long jail time if you own, buy, sell or deal crypto. That's it.
Force the compagny and bank to give crypto owner name. Anyway crypto site have our full name and info, we even have to pay income tax on it.
Laws can be done in one day.
You don't believe me? Look at everyone ...
You can also decode from b64 Q29udGFjdCBtZSBhdCBhZGl0ZWMzNUBnbWFpbC5jb20=
x = 55066263022277343669578718895168534326250603453777594175500187360389116729240
y = 32670510020758816978083085130507043184471273380659243275938904335757337482424
I applied x ^ 3, then added 7, then mod P on that webpage. Then I square rooted it and got