比特幣分層確定性錢包實現探究——03用助記詞生成RootSeed

到目前爲止我們能產生隨機的合法助記詞了，接下來我們要用這些助記詞生成RootSeed。

生成過程直接調用接口，但是裏面的原理卻很複雜。

這裏需要用到pbkdf2函數。關於這個函數的說明，在BIP39裏有，我就不翻譯了，內容如下：

To create a binary seed from the mnemonic, we use the PBKDF2 function with a mnemonic 
sentence (in UTF-8 NFKD) used as the password and the string "mnemonic" + passphrase 
(again in UTF-8 NFKD) used as the salt. The iteration count is set to 2048 and HMAC-SHA512 
is used as the pseudo-random function. The length of the derived key is 512 bits (= 64 bytes).

關於這裏的密碼，各個錢包用的密碼都不同，例如TREZOR硬件錢包使用“TREZOR”作爲密碼，也可以不用密碼，傳入空字符串。

實現代碼如下：

import (
	"crypto/sha512"
	"errors"
	"golang.org/x/crypto/pbkdf2"
	"strings"
)

//助記詞單詞之間一定要用空格隔開，不能用其他符號隔開
func Mnemonics2RootSeed(mnemonics, passphrase string) ([]byte, error) {
	words := strings.Split(mnemonics, " ")
	wordAmount := len(words)
	if !(wordAmount >= 12 && wordAmount <=24 && wordAmount%3==0) {
		return nil,errors.New("invalid mnmonic words")
	}
	return pbkdf2.Key([]byte(mnemonics), []byte("mnemonic"+passphrase), 2048, 64, sha512.New ),nil
}

測試代碼：

func TestMnemonicWords2RootSeed(t *testing.T) {
	//t.SkipNow()
	t.Run("test use words to generate root seed", func(t *testing.T) {
		var (
			words = "glow laugh acquire menu anchor evil occur put hover renew calm purpose"
			seed []byte
			err error
			want = "afab97eb2f25d6c4cd3ca02674ab362a3c851a7c81b017a411345453ce869cb09ff8508d359a1091f0eb1b52c988fc686dcc21b2e57129a8036ea351808c2ee5"
			got string
		)

		if seed,err = Mnemonics2RootSeed(words, "TREZOR"); err != nil {
			t.Error(err)
			return
		}

		got = hex.EncodeToString(seed)
		if want != got {
			t.Error("error seed")
			t.Error("want:", want)
			t.Error("got:", got)
		}
	})
}

（全文完）

參考鏈接：

https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki