Intro

Computers are pretty bad at creating random numbers. These can be  easily predicted. For this reason we need some outside event to create  an entropy pool that can be used to create real random numbers. We use a pair of hexadecimal dice to make sure the data for our entropy pool is created from real random output.

--extra-entropy

monero-wallet-cli supports the command line option --extra-entropy. 

--extra-entropy arg        File containing extra entropy to initialize the PRNG (any data, aim for 256 bits of entropy to be useful, which typically means more than 256 bits of data).

--extra-entropy reads random data from a binary file - but first we need to roll some dice.

Dice

The hexadecimal dice contains the following numbers: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F. Two hexadecimal numbers require one byte of memory. e.G. You roll two F. (F,F) = 255 in decimal => 1 byte = 8 bit. To create 256 bits of data (entropy) we need to roll the two dice at least 32 times. 256 bit/8 bit = 32. For one dice you need to roll double the amount - 64 times. Make sure you buy two different colored dice or mark one dice with a  dot. Always write down the number on the marked dice first. Your brain  could be biased and always write down the smaller number first. We want  to avoid such behavior.

Create some entropy

The sequence after echo is where we write down the result of our dice. In this example i have rolled the dice 40 times to be on the safe side.

export HISTFILE=/dev/null

echo 50F38D07032E63933A5317D8FE3E0B4ED92560ABE310CC98BCFA54F3B196B2CC3FA219A494C49A7C | xxd -r -p > /dev/shm/entropy

xxd writes the hex sequence to a file. Try to avoid writing the file on a hard drive. /dev/shm is shared memory that can be used for this purpose. export HISTFILE=/dev/null makes sure that linux wont write the following command in the .bash_history.

Create a new wallet

At last we can create a new wallet.

./monero-wallet-cli --generate-new-wallet mywallet --extra-entropy /dev/shm/entropy

rm /dev/shm/entropy

Protect your wallet with a passphrase.

--generate-new-wallet creates a mnemonic seed of 25 words.  Please write down those 25 words on a piece of paper and keep it safe.  With the mnemonic seed you can restore your wallet if it gets lost.