seed.go

// Copyright © 2018 Weald Technology Trading
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package ed25519hd provides hierarchical derivation of ED255-19 keys.
package ed25519hd

import (
	"crypto/sha256"
	"crypto/sha512"
	"fmt"
	"math/big"
	"strings"

	"golang.org/x/crypto/pbkdf2"
	"golang.org/x/text/unicode/norm"
)

// SeedFromMnemonic takes a BIP39 mnemonic and generates a seed.
func SeedFromMnemonic(mnemonic string, passphrase string) ([]byte, error) {
	// Convert mnemonic and passphrase to NFKD
	mnemonic = norm.NFKD.String(mnemonic)
	passphrase = norm.NFKD.String(passphrase)

	valid, err := ValidateMnemonic(mnemonic)
	if !valid {
		return nil, err
	}

	return pbkdf2.Key([]byte(mnemonic), []byte("mnemonic"+passphrase), 2048, 64, sha512.New), nil
}

// ValidateMnemonic returns true if the mnemonic is valid.
// Note that this expects mnemonics to be of 24 words; other lengths are not supported.
func ValidateMnemonic(mnemonic string) (bool, error) {
	words := strings.Split(mnemonic, " ")
	if len(words) != 24 {
		return false, fmt.Errorf("mnemonic must be 24 words (found %d)", len(words))
	}

	// Ensure that the checksum is valid
	seed := big.NewInt(0)
	for i, word := range words {
		index, exists := reverseWordMap[word]
		if !exists {
			return false, fmt.Errorf("invalid mnemonic word %s at position %d", word, i+1)
		}
		indexVal := big.NewInt(int64(index))
		seed = seed.Lsh(seed, 11)
		seed = seed.Or(seed, indexVal)
	}

	// At this point the seed contains a checksum in the last 8 bits.  This should match the first 8 bits of the sha256() of the
	// seed without the checksum
	noChecksumSeed := big.NewInt(0).Set(seed)
	noChecksumSeed = noChecksumSeed.Rsh(noChecksumSeed, 8)
	checksum := sha256.Sum256(noChecksumSeed.Bytes())
	if seed.Bytes()[32] != checksum[0] {
		return false, fmt.Errorf("invalid mnemonic checksum")
	}

	return true, nil
}

var reverseWordMap = map[string]int{}

func init() {
	for i, v := range englishWordList {
		reverseWordMap[v] = i
	}
}

var englishWordList = strings.Split(`abandon
ability
able
about
above
absent
absorb
abstract
absurd
abuse
access
accident
account
accuse
achieve
acid
acoustic
acquire
across
act
action
actor
actress
actual
adapt
add
addict
address
adjust
admit
adult
advance
advice
aerobic
affair
afford
afraid
again
age
agent
agree
ahead
aim
air
airport
aisle
alarm
album
alcohol
alert
alien
all
alley
allow
almost
alone
alpha
already
also
alter
always
amateur
amazing
among
amount
amused
analyst
anchor
ancient
anger
angle
angry
animal
ankle
announce
annual
another
answer
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antique
anxiety
any
apart
apology
appear
apple
approve
april
arch
arctic
area
arena
argue
arm
armed
armor
army
around
arrange
arrest
arrive
arrow
art
artefact
artist
artwork
ask
aspect
assault
asset
assist
assume
asthma
athlete
atom
attack
attend
attitude
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auction
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author
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average
avocado
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bachelor
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balance
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bamboo
banana
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barely
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barrel
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beach
bean
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become
beef
before
begin
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behind
believe
below
belt
bench
benefit
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betray
better
between
beyond
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bid
bike
bind
biology
bird
birth
bitter
black
blade
blame
blanket
blast
bleak
bless
blind
blood
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blouse
blue
blur
blush
board
boat
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boil
bomb
bone
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