Hashes are impossible by hand...

Wouldn't a LiveCD on an offline HDD-less PC enough?

I haven't looked at the details of the hashing algorithm used to generate the public address from the private key. However, I don't think impossible is correct. I mean, everything a computer does can (in principle) be simulated using a very long tape and a pencil (see universal Turing machine).

Im just saying, difficult/tedious != impossible.

You want to play with semantics?

Ok, let's play.

Let's take a human, the super-hero kind, who can:

a/ Calculate a 32-bit operation in 10 seconds

b/ Work from midnight to midnight everyday

c/ Calculate a 32-bit operation without any errors

A hash takes about 5000 32-bit operations. So make it 10000 for ripemd160(sha256()).

That makes (10*10000) = 100k seconds = 38.4 hours = 1.6 day non-stop.

Possible.

Now here comes the fun.

This time we take a real human, the super smart kind.

A/ He calculates a 32-bit operation in 30 seconds (please try a 32-bit addition and tell me how much time it took)

This raises the total time to calculate one hash to 115.2 hours

B/ The guy must sleep, so he can "only" work from 8am to midnight.

This makes the total time to calculate one hash equal to 4.8 days.

Still possible.

C/ The lower brain failure rate

**in the best conditions** is 5%. As he's super smart his is only 1%.

The probability of him finding the correct hash on one try is P = 1/2^(100000*1%) = 1/2^1000 ~ 1/10^300

D/ He starts the hashing calculation at birth and will stop at 100 years old.

This is (100*365) = 36500 days of calculation.

One try is 4.8 days, so he has 7604 tries available.

The odd of our super smart guy FINDING AT LEAST ONCE the correct hash in his entire lifetime is then:

R = 1-Q where Q = (1-P)^7604 = ( 1 - 1/2^1000 )^7604

Basic maths gives that Q > 1 - 7604/2^1000 = 1 - 10^(-297.149) > 1 - 10^(-297)

So R < 10^(-297) < 1/2^986

Yes, R < 1/2^986

**TLDR**It's easier to crack 6 different bitcoin addresses with only 6 guesses than to a human to calculate a correct bitcoin address hash in his lifetime

Yes, I call that impossible