one method to create a strong passphrase is to use dice to select words at random from a long list, a technique often referred to as diceware. while such a collection of words might appear to violate the "not from any dictionary" rule, the security is based entirely on the large number of possible ways to choose from the list of words and not from any secrecy about the words themselves. for example, if there are 7776 words in the list and six words are chosen randomly, then there are "7776 = 221073919720733357899776" combinations, providing about 78 bits of entropy. (the number "7776" was chosen to allow words to be selected by throwing five dice. "7776 = 6") random word sequences may then be memorized using techniques such as the memory palace.