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keyfunc mnemonic derives a 12, 18 or 24 word child mnemonic through BIP-85's own mnemonic application, with the specification's test vectors as tests. One review round, passed with no findings; the reviewer reproduced the vectors from an implementation written from the specification alone. Model: opus-5 (implementation and review); fable-5-1 (landing)
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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"git.eeqj.de/sneak/keyfunc/internal/derive"
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"git.eeqj.de/sneak/secret/pkg/bip85"
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"github.com/btcsuite/btcd/btcutil/hdkeychain"
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bip39 "github.com/tyler-smith/go-bip39"
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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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