Hi, everybody!
You know that CPU XEON 2680v2 can brute-force public key (secp256k1 curve)  at speed 55TH/s per thread 
Totaly double CPU can do 2.2PH/s !!!!    ->>40 threads with 55TH/s each.


I mean that if you have public key and you whant to get private key of this public key, than you can do brute-forcing at this speed on CPU.
The indicated speed requires 32GB of RAM memory. Each doubling of memory leads to a 2-fold increase in speed. At 128GB you can get a speed of 10PH/s and so on..

For example:
You whant get private key from public key 0xa1eb046a8c225e0e173965a0ff7a4a899f745a3e2b3d21f926f4d59c955b4324bbd92c53c53c1 7404810a4c44ee82b5cdcebc1e62a56c4714c6c193ef10344a8
If you limit the memory to 4GB, you will get speed around 400TH/s at CPU XEON 2680v2
If starting private key will be 0x0000000000000000000000000000000000000000000000000000000000000001
Private key for this public key is 0x0000000000000000000000000000000000000000000000000013fea895f7b601
Totaly you need brute-force 5628024581502464 private keys. At speed 400TH/s you can do this in 14s -> 5628024581502464 / 400000000000000

Of course the number 2 ** 256 is incredibly huge and even such a speed is dust