Hello, daigo!

Take for instance this passphrase: "dog.cat.mouse" (which is inclusive

of the periods but exclusive of the quotations, so a total of 13 characters)

The goal is to guess this passphrase, using the set of American English alphabet,

both lowercase and uppercase, positive numbers 0-9, and the following symbols:

[ ] \ ; ' / , . . . So that's a total of 70 characters.

A total of 30,000,000,000 (thirty billion) guesses are possible every 1 second.

The length of the passphrase is unknown.

What is the probability that this passphrase will be guessed within 500 years?

If the passphrase is characters long, there are possible passphrases.

How many guesses can be made in 500 years?