Recovery Phrases

Motivation

We define a way for easily entering and writing down arbitrary binary seeds using
a simple dictionary of known words (available in many different languages).

The motivation here is to have sentence of words easy to read and write for humans,
which map uniquely back and forth to a sized binary data (harder to remember).

Encoding

The process describing how to encode recovery phrases is described in BIP-0039
section "Generating the mnemonic". Below is a reformulation of this specification.

We call Entropy an arbitrary sequence of bytes that has been generated through high
quality randomness methods. The allowed size of Entropy is 96-256 bits and is
necessarily a multiple of 32 bits (4 bytes).

A checksum is appended to the initial entropy by taking the first ENT / 32 bits
of the SHA256 hash of it, where ENT designates the Entropy size in bits.

Then, the concatenated result is split into groups of 11 bits, each encoding a number
from 0 to 2047 serving as an index into a known dictionary (see below).

Sentence Length	Entropy Size	Checksum Size
9 words	96 bits (12 bytes)	3 bits
12 words	128 bits (16 bytes)	4 bits
15 words	160 bits (20 bytes)	5 bits
18 words	192 bits (24 bytes)	6 bits
21 words	224 bits (28 bytes)	7 bits
24 words	256 bits (32 bytes)	8 bits

Dictionaries

Topl uses the same dictionaries as defined in BIP-0039.