mirror of
https://github.com/luxfi/threshold.git
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zeekay
3da6ad92e4
- Remove unnecessary trailing newlines - Fix comment formatting - Adjust indentation and spacing - Remove unused nolint directives
43 lines
1.1 KiB
Go
43 lines
1.1 KiB
Go
package bip32
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import (
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"crypto/hmac"
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"crypto/sha512"
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"encoding/binary"
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"fmt"
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"github.com/luxfi/threshold/pkg/math/curve"
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)
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// DeriveScalar uses a public point, chaining value, and index, to derive a scalar and chaining value.
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//
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// This scalar should be added to the secret key.
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//
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// If an error is returned, this means that this index will not be useable, and another
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// index should be used instead.
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//
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// This function will panic if an index for a hardened key is used.
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//
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// See: https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki
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func DeriveScalar(public *curve.Secp256k1Point, chaining []byte, i uint32) (*curve.Secp256k1Scalar, []byte, error) {
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if i>>31 != 0 {
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panic("DeriveScalar doesn't work with hardened keys.")
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}
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h := hmac.New(sha512.New, chaining)
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compressed, _ := public.MarshalBinary()
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_, _ = h.Write(compressed)
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iBytes := make([]byte, 4)
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binary.BigEndian.PutUint32(iBytes, i)
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h.Write(iBytes)
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out := h.Sum(nil)
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scalar := new(curve.Secp256k1Scalar)
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err := scalar.UnmarshalBinary(out[:32])
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if err != nil || scalar.IsZero() {
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return nil, nil, fmt.Errorf("bad index: %d", i)
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}
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return scalar, out[32:], nil
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}
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