is there any free bitcoin private key generator software on the internet?i have only the public key.thanks

Given the fact you only have a public key, there is no way you can generate a private key for that. Do not even attempt.

Those who say they can are scammers.

You can use openssl to generate the 256bit ECDSA private key

openssl ecparam -genkey -name secp256k1 -rand /dev/urandom -out privatekey.pem

However:

2^256 = 1.1x10^77 = number of key combinations

2^128 = 3.4x10^38 = the average number of guesses needed

According to this website: http://en.wikipedia.org/wiki/TOP500, the fastest supercomputer is the K computer which has 10.51 petaflops. A petaflop is 10^15 FLOPS, floating point instructions per second.

So far so good, but I need to know how many FLOPS are needed per guess?

[I will venture a guess:]

Between 1,000 and 10,000 FLOPS (or integer equivalents) per guess.

10.51x10^15 ops/second / 1000 to 10000 ops/guess) = 10.51x10^12 to 10.51x10^11 guess/second.

3.4x10^38 guesses/crack / 10.51x10^12 guess/second = 3.2x10^25 seconds.

3.2x10^25 seconds / 60 seconds/minute / 60 minutes/hour / 24 hours/day / 365.25 days/year = 1.01x10^18 years

1.01x10^18 years / 1x10^9 / 1x10^9 = 1.014 to 10.014 billion billion years.

Let me know how much Bitcoin is worth in 10.014 billion billion years please.

Stay Fishy