We can generate our own private keys with the specified parameters in multiple ways. Manual methods such as Rolling dice ny converting the results into binary and derive the bitcoin address from it or using the python script.
Hmmm... I think I do understand the concept now. Before now I've actually come across other methods of private key generation but now I get the concept why some generation approaches are safer than others. Basically what it simply means is that the OP generated his keys with an algorithm with a lower entropy than regular key generation processes.
I made my calculations for this scenario but in anyway with or without the lowercase it is impossible to break even if the entropy is around 103 bits.
Exactly but I think that means that although OP's entropy of 36
40 in contrast to 62
40 is of lower difficulty, still the difference in security level is almost same since both can't be brute forced.