mirror of
https://github.com/bitcoinbook/bitcoinbook
synced 2024-11-26 09:58:22 +00:00
130 lines
4.8 KiB
Plaintext
130 lines
4.8 KiB
Plaintext
<pre>
|
|
BIP: BIP-0039
|
|
Title: Mnemonic code for generating deterministic keys
|
|
Authors: Marek Palatinus <slush@satoshilabs.com>
|
|
Pavol Rusnak <stick@satoshilabs.com>
|
|
ThomasV <thomasv@bitcointalk.org>
|
|
Aaron Voisine <voisine@gmail.com>
|
|
Sean Bowe <ewillbefull@gmail.com>
|
|
Status: Draft
|
|
Type: Standards Track
|
|
Created: 2013-09-10
|
|
</pre>
|
|
|
|
==Abstract==
|
|
|
|
This BIP describes the implementation of a mnemonic code or mnemonic sentence --
|
|
a group of easy to remember words -- for the generation of deterministic wallets.
|
|
|
|
It consists of two parts: generating the mnenomic, and converting it into a
|
|
binary seed. This seed can be later used to generate deterministic wallets using
|
|
BIP-0032 or similar methods.
|
|
|
|
==Motivation==
|
|
|
|
A mnenomic code or sentence is superior for human interaction compared to the
|
|
handling of raw binary or hexidecimal representations of a wallet seed. The
|
|
sentence could be written on paper or spoken over the telephone.
|
|
|
|
This guide meant to be as a way to transport computer-generated randomnes over
|
|
human readable transcription. It's not a way how to process user-created
|
|
sentences (also known as brainwallet) to wallet seed.
|
|
|
|
==Generating the mnemonic==
|
|
|
|
The mnemonic must encode entropy in any multiple of 32 bits. With larger entropy
|
|
security is improved but the sentence length increases. We can refer to the
|
|
initial entropy length as ENT. The recommended size of ENT is 128-256 bits.
|
|
|
|
First, an initial entropy of ENT bits is generated. A checksum is generated by
|
|
taking the first <pre>ENT / 32</pre> bits of its SHA256 hash. This checksum is
|
|
appended to the end of the initial entropy. Next, these concatenated bits are
|
|
are split into groups of 11 bits, each encoding a number from 0-2047, serving
|
|
as an index to a wordlist. Later, we will convert these numbers into words and
|
|
use the joined words as a mnemonic sentence.
|
|
|
|
The following table describes the relation between the initial entropy
|
|
length (ENT), the checksum length (CS) and length of the generated mnemonic
|
|
sentence (MS) in words.
|
|
|
|
<pre>
|
|
CS = ENT / 32
|
|
MS = (ENT + CS) / 11
|
|
|
|
| ENT | CS | ENT+CS | MS |
|
|
+-------+----+--------+------+
|
|
| 128 | 4 | 132 | 12 |
|
|
| 160 | 5 | 165 | 15 |
|
|
| 192 | 6 | 198 | 18 |
|
|
| 224 | 7 | 231 | 21 |
|
|
| 256 | 8 | 264 | 24 |
|
|
</pre>
|
|
|
|
==Wordlist==
|
|
|
|
An ideal wordlist has the following characteristics:
|
|
|
|
a) smart selection of words
|
|
- wordlist is created in such way that it's enough to type the first four
|
|
letters to unambiguously identify the word
|
|
|
|
b) similar words avoided
|
|
- word pairs like "build" and "built", "woman" and "women", or "quick" and "quickly"
|
|
not only make remembering the sentence difficult, but are also more error
|
|
prone and more difficult to guess
|
|
|
|
c) sorted wordlists
|
|
- wordlist is sorted which allows for more efficient lookup of the code words
|
|
(i.e. implementation can use binary search instead of linear search)
|
|
- this also allows trie (prefix tree) to be used, e.g. for better compression
|
|
|
|
The wordlist can contain native characters, but they have to be encoded in UTF-8
|
|
using Normalization Form Compatibility Decomposition (NFKD).
|
|
|
|
==From mnemonic to seed==
|
|
|
|
A user may decide to protect their mnemonic by passphrase. If a passphrase is not
|
|
present, an empty string "" is used instead.
|
|
|
|
To create a binary seed from the mnemonic, we use PBKDF2 function with a mnemonic
|
|
sentence (in UTF-8 NFKD) used as a password and string "mnemonic" + passphrase (again
|
|
in UTF-8 NFKD) used as a salt. Iteration count is set to 2048 and HMAC-SHA512 is used as
|
|
a pseudo-random function. Desired length of the derived key is 512 bits (= 64 bytes).
|
|
|
|
This seed can be later used to generate deterministic wallets using BIP-0032 or
|
|
similar methods.
|
|
|
|
The conversion of the mnemonic sentence to binary seed is completely independent
|
|
from generating the sentence. This results in rather simple code; there are no
|
|
constraints on sentence structure and clients are free to implement their own
|
|
wordlists or even whole sentence generators, allowing for flexibility in wordlists
|
|
for typo detection or other purposes.
|
|
|
|
Although using mnemonic not generated by algorithm described in "Generating the
|
|
mnemonic" section is possible, this is not advised and software must compute
|
|
checksum of the mnemonic sentence using wordlist and issue a warning if it is
|
|
invalid.
|
|
|
|
Described method also provides plausible deniability, because every passphrase
|
|
generates a valid seed (and thus deterministic wallet) but only the correct one
|
|
will make the desired wallet available.
|
|
|
|
==Wordlists==
|
|
|
|
* [[bip-0039/english.txt|English]]
|
|
|
|
==Test vectors==
|
|
|
|
See https://github.com/trezor/python-mnemonic/blob/master/vectors.json
|
|
|
|
==Reference Implementation==
|
|
|
|
Reference implementation including wordlists is available from
|
|
|
|
http://github.com/trezor/python-mnemonic
|
|
|
|
==Other Implementations==
|
|
|
|
Objective-C - https://github.com/nybex/NYMnemonic
|
|
|