The End of Money Quotes

“For example, multiplying two six-digit prime numbers like 323,123 and 596,977 together is a relatively easy task. With a minute and a pencil and paper, you would get 192,896,999,171. But if instead you were given the number 192,896,999,171 and asked to find the two prime numbers that divide it, you would need a lot more time to test all of the different possibilities. In public-key encryption the numbers are much larger, but computers have to perform very similar tasks.”
― New Scientist, The End of Money: The story of bitcoin, cryptocurrencies and the blockchain revolution