# Constant N defining the order of the secp256k1 elliptic curve group
N = (1 << 256) - 0x14551231950B75FC4402DA1732FC9BEBF

import secrets

def generate_private_key():
    # Generate a random number in the range [1, N-1]
    private_key = secrets.randbelow(N - 1) + 1
    # Convert to HEX format with leading zeros to ensure 64 characters
    private_key_hex = f'{private_key:064x}'
    return private_key_hex

# Example usage
private_key_hex = generate_private_key()
print(private_key_hex)