# Determine the first byte of the compressed public key based on the private key's sign
if private_key_int < 0:
public_key_bytes_compressed = (
b"\x03" + vk.to_string()[:32] if vk.to_string()[-1] % 2 == 0 else b"\x02" + vk.to_string()[:32]
)
else:
public_key_bytes_compressed = (
b"\x02" + vk.to_string()[:32] if vk.to_string()[-1] % 2 == 0 else b"\x03" + vk.to_string()[:32]
)
You code is incorrect. The 0x02, 0x03 prefixes are based only on the value of the public key.
Furthermore, a valid secp256k1 private key is an integer in the range 1 to FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364140, so testing if it is less than 0 should always return false. If your test returns true, then the private key is invalid or there is a bug in your code.
Since the program itself knows the private key, the public key output result is 100% accurate.
There are no errors in the program.
Please check the private key and the outputted public key.
So you've been told twice already that you're doing things incorrectly, but you insist on it being 100% correct and error-free. Why do you need our opinion in that case?
Public keys for private keys "-1" and N-1 are identical, while your code messes up their compressed representation (since you have a logical contradiction at the reasoning layer, since private keys don't have a sign, since a modular interval doesn't have negative values). So before all else, if your code was Windows 95, this would become a BSOD of the brain.