So, I create my Entropy by doing my 256 coins flips, what I have to do next to end-up with a valid 24 words mnemonic ?
Try reading and following the process as described in BIP39:
First, an initial entropy of ENT bits is generated. A checksum is generated by taking the first
ENT / 32
bits of its SHA256 hash. This checksum is appended to the end of the initial entropy. Next, these concatenated bits are split into groups of 11 bits, each encoding a number from 0-2047, serving as an index into a wordlist. Finally, we convert these numbers into words and use the joined words as a mnemonic sentence.
So the process would be:
1. Take your 256 bits of ENT (your coin fips), calculate the SHA256 hash, and then calculate the checksum which is the first 8 bits (256/32)
from the hash.
2. Add those 8 bits to the END of your 256 flips, you now have a total of 264 bits
3. Divide into 11 bit chunks, you'll get 24x 11 bit sequences
4. Convert each 11 bit sequence into a decimal number. ie. 10011101101 => 1261
5. Lookup the number in
the 2048 word list. NOTE: The list as displayed on GitHub is indexed from 1-2048, but the numbers you are generating are from 0-2047, so you need to add one to your converted decimal number to match the github list... so, 1261 + 1 = 1262 => oval
6. Repeat Steps 4. and 5. until you have converted all 24 chunks into words.
Congrats, you now have a 24 word seed
mnemonic generated from coin flips.