status-go/extkeys/utils.go

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package extkeys
import (
"crypto/hmac"
"crypto/sha512"
"errors"
"math/big"
"github.com/btcsuite/btcd/btcec"
)
// errors
var (
ErrInvalidSecretKey = errors.New("generated secret key cannot be used")
)
func splitHMAC(seed, salt []byte) (secretKey, chainCode []byte, err error) {
data := hmac.New(sha512.New, salt)
if _, err = data.Write(seed); err != nil {
return
}
I := data.Sum(nil)
// Split I into two 32-byte sequences, IL and IR.
// IL = master secret key
// IR = master chain code
secretKey = I[:32]
chainCode = I[32:]
// IL (secretKey) is expected to be a 256-bit integer (it is used as parse256(IL)),
// and consequently that integer must be within range for SECP256k1 private key.
//
// There's tiny possibility (<1 in 2^127) this invariant is violated:
// error is returned in that case, and simple resolution is to request another child with i incremented.
keyBigInt := new(big.Int).SetBytes(secretKey)
if keyBigInt.Cmp(btcec.S256().N) >= 0 || keyBigInt.Sign() == 0 {
err = ErrInvalidSecretKey
}
return
}
// paddedAppend appends the src byte slice to dst, returning the new slice.
// If the length of the source is smaller than the passed size, leading zero
// bytes are appended to the dst slice before appending src.
func paddedAppend(size uint, dst, src []byte) []byte {
for i := 0; i < int(size)-len(src); i++ {
dst = append(dst, 0)
}
return append(dst, src...)
}