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4e04ee39a7
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sneak/secret now carries its own copy of go-bip39 (sneak/secret#130), so requiring it at that commit, ef0ae90, lets go mod tidy drop go-bip39 from go.sum. Earlier, secret renamed its module to sneak.berlin/go/secret (sneak/secret#43), so the requirement, the two imports of its bip85 package and the README sentence naming that package move to the new path. The bip85 functions keyfunc calls are unchanged, and no other requirement moves. Model: opus-5-5
64 lines
1.7 KiB
Go
64 lines
1.7 KiB
Go
// Package childmnemonic derives a mnemonic from another mnemonic.
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package childmnemonic
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import (
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"errors"
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"fmt"
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"github.com/btcsuite/btcd/btcutil/hdkeychain"
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"sneak.berlin/go/keyfunc/internal/bip39"
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"sneak.berlin/go/keyfunc/internal/derive"
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"sneak.berlin/go/secret/pkg/bip85"
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)
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// english is the number BIP-85 gives the English word list.
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const english = 0
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// The lengths a child mnemonic may have. BIP-85 also allows 15 and 21
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// words; these three are the ones this tool offers.
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const (
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twelve = 12
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eighteen = 18
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twentyFour = 24
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)
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// DefaultWords is how long a child mnemonic is when the user does not
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// say.
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const DefaultWords = twelve
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// ErrWordCount is returned for a length this tool does not offer.
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var ErrWordCount = errors.New("a child mnemonic has 12, 18 or 24 words")
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// Derive returns the English child mnemonic of that many words at that
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// key index, taken from the master key with BIP-85's own mnemonic
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// application, number 39. The words come straight from the BIP-85
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// entropy, cut to the length the word count needs, rather than from
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// the generator the other key types read their bytes from.
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func Derive(
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master *hdkeychain.ExtendedKey,
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words, index uint32,
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) (string, error) {
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switch words {
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case twelve, eighteen, twentyFour:
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default:
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return "", fmt.Errorf("%w, not %d", ErrWordCount, words)
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}
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err := derive.CheckIndex(index)
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if err != nil {
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return "", err
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}
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entropy, err := bip85.DeriveBIP39Entropy(master, english, words, index)
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if err != nil {
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return "", fmt.Errorf("deriving entropy: %w", err)
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}
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child, err := bip39.NewMnemonic(entropy)
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if err != nil {
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return "", fmt.Errorf("turning the entropy into words: %w", err)
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}
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return child, nil
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}
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