wallet - deterministic secret derivation

.gitignore

@@ -0,0 +1,3 @@
+cmd/nutw/nutw
+**/.env
+*.txt

cashu/nuts/nut13/nut13.go

@@ -0,0 +1,83 @@
+package nut13
+
+import (
+	"encoding/binary"
+	"encoding/hex"
+
+	"github.com/btcsuite/btcd/btcutil/hdkeychain"
+	"github.com/decred/dcrd/dcrec/secp256k1/v4"
+)
+
+func DeriveKeysetPath(master *hdkeychain.ExtendedKey, keysetId string) (*hdkeychain.ExtendedKey, error) {
+	keysetBytes, err := hex.DecodeString(keysetId)
+	if err != nil {
+		return nil, err
+	}
+	bigEndianBytes := binary.BigEndian.Uint64(keysetBytes)
+	keysetIdInt := bigEndianBytes % (1<<31 - 1)
+
+	// m/129372
+	purpose, err := master.Derive(hdkeychain.HardenedKeyStart + 129372)
+	if err != nil {
+		return nil, err
+	}
+
+	// m/129372'/0'
+	coinType, err := purpose.Derive(hdkeychain.HardenedKeyStart + 0)
+	if err != nil {
+		return nil, err
+	}
+
+	// m/129372'/0'/keyset_k_int'
+	keysetPath, err := coinType.Derive(hdkeychain.HardenedKeyStart + uint32(keysetIdInt))
+	if err != nil {
+		return nil, err
+	}
+
+	return keysetPath, nil
+}
+
+func DeriveBlindingFactor(keysetPath *hdkeychain.ExtendedKey, counter uint32) (*secp256k1.PrivateKey, error) {
+	// m/129372'/0'/keyset_k_int'/counter'
+	counterPath, err := keysetPath.Derive(hdkeychain.HardenedKeyStart + counter)
+	if err != nil {
+		return nil, err
+	}
+
+	// m/129372'/0'/keyset_k_int'/counter'/1
+	rDerivationPath, err := counterPath.Derive(1)
+	if err != nil {
+		return nil, err
+	}
+
+	rkey, err := rDerivationPath.ECPrivKey()
+	if err != nil {
+		return nil, err
+	}
+
+	return rkey, nil
+}
+
+func DeriveSecret(keysetPath *hdkeychain.ExtendedKey, counter uint32) (string, error) {
+	// m/129372'/0'/keyset_k_int'/counter'
+	counterPath, err := keysetPath.Derive(hdkeychain.HardenedKeyStart + counter)
+	if err != nil {
+		return "", err
+	}
+
+	// m/129372'/0'/keyset_k_int'/counter'/0
+	secretDerivationPath, err := counterPath.Derive(0)
+	if err != nil {
+		return "", err
+	}
+
+	secretKey, err := secretDerivationPath.ECPrivKey()
+	if err != nil {
+		return "", err
+	}
+
+	secretBytes := secretKey.Serialize()
+	secret := hex.EncodeToString(secretBytes)
+
+	return secret, nil
+}

cashu/nuts/nut13/nut13_test.go

@@ -0,0 +1,74 @@
+package nut13
+
+import (
+	"encoding/hex"
+	"testing"
+
+	"github.com/btcsuite/btcd/btcutil/hdkeychain"
+	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/tyler-smith/go-bip39"
+)
+
+func TestSecretDerivation(t *testing.T) {
+	mnemonic := "half depart obvious quality work element tank gorilla view sugar picture humble"
+	keysetId := "009a1f293253e41e"
+
+	seed := bip39.NewSeed(mnemonic, "")
+	master, err := hdkeychain.NewMaster(seed, &chaincfg.MainNetParams)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	keysetPath, err := DeriveKeysetPath(master, keysetId)
+	if err != nil {
+		t.Fatalf("could not derive keyset path: %v", err)
+	}
+
+	secrets := make([]string, 5)
+	rs := make([]string, 5)
+
+	var i uint32 = 0
+	for ; i < 5; i++ {
+		secret, err := DeriveSecret(keysetPath, i)
+		if err != nil {
+			t.Fatalf("error deriving secret: %v", err)
+		}
+		secrets[i] = secret
+
+		rkey, err := DeriveBlindingFactor(keysetPath, i)
+		if err != nil {
+			t.Fatalf("error deriving r: %v", err)
+		}
+
+		rbytes := rkey.Serialize()
+		r := hex.EncodeToString(rbytes)
+		rs[i] = r
+	}
+
+	expectedSecrets := []string{
+		"485875df74771877439ac06339e284c3acfcd9be7abf3bc20b516faeadfe77ae",
+		"8f2b39e8e594a4056eb1e6dbb4b0c38ef13b1b2c751f64f810ec04ee35b77270",
+		"bc628c79accd2364fd31511216a0fab62afd4a18ff77a20deded7b858c9860c8",
+		"59284fd1650ea9fa17db2b3acf59ecd0f2d52ec3261dd4152785813ff27a33bf",
+		"576c23393a8b31cc8da6688d9c9a96394ec74b40fdaf1f693a6bb84284334ea0",
+	}
+
+	expectedRs := []string{
+		"ad00d431add9c673e843d4c2bf9a778a5f402b985b8da2d5550bf39cda41d679",
+		"967d5232515e10b81ff226ecf5a9e2e2aff92d66ebc3edf0987eb56357fd6248",
+		"b20f47bb6ae083659f3aa986bfa0435c55c6d93f687d51a01f26862d9b9a4899",
+		"fb5fca398eb0b1deb955a2988b5ac77d32956155f1c002a373535211a2dfdc29",
+		"5f09bfbfe27c439a597719321e061e2e40aad4a36768bb2bcc3de547c9644bf9",
+	}
+
+	for i := 0; i < 5; i++ {
+		if expectedSecrets[i] != secrets[i] {
+			t.Fatalf("secret at index: %v does not match. Expected '%v' but got '%v'", i, expectedSecrets[i], secrets[i])
+		}
+
+		if expectedRs[i] != rs[i] {
+			t.Fatalf("r at index: %v does not match. Expected '%v' but got '%v'", i, expectedRs[i], rs[i])
+		}
+	}
+
+}

crypto/keyset.go

@@ -15,8 +15,7 @@ import (
 const maxOrder = 64
 
 type Keyset struct {
-	Id string
-	//MintURL string
+	Id     string
 	Unit   string
 	Active bool
 	Keys   map[uint64]KeyPair
@@ -36,7 +35,7 @@ type WalletKeyset struct {
 	Unit       string
 	Active     bool
 	PublicKeys map[uint64]*secp256k1.PublicKey
-	Counter    uint64
+	Counter    uint32
 }
 
 func GenerateKeyset(seed, derivationPath string) *Keyset {
@@ -130,7 +129,6 @@ func (ks *Keyset) UnmarshalJSON(data []byte) error {
 	}
 
 	ks.Id = temp.Id
-	//ks.MintURL = temp.MintURL
 	ks.Unit = temp.Unit
 	ks.Active = temp.Active
 
@@ -181,3 +179,57 @@ func (kp *KeyPair) UnmarshalJSON(data []byte) error {
 
 	return nil
 }
+
+type WalletKeysetTemp struct {
+	Id         string
+	MintURL    string
+	Unit       string
+	Active     bool
+	PublicKeys map[uint64][]byte
+	Counter    uint32
+}
+
+func (wk *WalletKeyset) MarshalJSON() ([]byte, error) {
+	temp := &WalletKeysetTemp{
+		Id:      wk.Id,
+		MintURL: wk.MintURL,
+		Unit:    wk.Unit,
+		Active:  wk.Active,
+		PublicKeys: func() map[uint64][]byte {
+			m := make(map[uint64][]byte)
+			for k, v := range wk.PublicKeys {
+				m[k] = v.SerializeCompressed()
+			}
+			return m
+		}(),
+		Counter: wk.Counter,
+	}
+
+	return json.Marshal(temp)
+}
+
+func (wk *WalletKeyset) UnmarshalJSON(data []byte) error {
+	temp := &WalletKeysetTemp{}
+
+	if err := json.Unmarshal(data, &temp); err != nil {
+		return err
+	}
+
+	wk.Id = temp.Id
+	wk.MintURL = temp.MintURL
+	wk.Unit = temp.Unit
+	wk.Active = temp.Active
+	wk.Counter = temp.Counter
+
+	wk.PublicKeys = make(map[uint64]*secp256k1.PublicKey)
+	for k, v := range temp.PublicKeys {
+		kp, err := secp256k1.ParsePubKey(v)
+		if err != nil {
+			return err
+		}
+
+		wk.PublicKeys[k] = kp
+	}
+
+	return nil
+}

go.mod

@@ -148,6 +148,7 @@ require (
 	github.com/tklauser/go-sysconf v0.3.12 // indirect
 	github.com/tklauser/numcpus v0.6.1 // indirect
 	github.com/tmc/grpc-websocket-proxy v0.0.0-20201229170055-e5319fda7802 // indirect
+	github.com/tyler-smith/go-bip39 v1.1.0 // indirect
 	github.com/xeipuuv/gojsonpointer v0.0.0-20190905194746-02993c407bfb // indirect
 	github.com/xeipuuv/gojsonreference v0.0.0-20180127040603-bd5ef7bd5415 // indirect
 	github.com/xeipuuv/gojsonschema v1.2.0 // indirect

go.sum

@@ -630,6 +630,8 @@ github.com/tklauser/numcpus v0.6.1 h1:ng9scYS7az0Bk4OZLvrNXNSAO2Pxr1XXRAPyjhIx+F
 github.com/tklauser/numcpus v0.6.1/go.mod h1:1XfjsgE2zo8GVw7POkMbHENHzVg3GzmoZ9fESEdAacY=
 github.com/tmc/grpc-websocket-proxy v0.0.0-20201229170055-e5319fda7802 h1:uruHq4dN7GR16kFc5fp3d1RIYzJW5onx8Ybykw2YQFA=
 github.com/tmc/grpc-websocket-proxy v0.0.0-20201229170055-e5319fda7802/go.mod h1:ncp9v5uamzpCO7NfCPTXjqaC+bZgJeR0sMTm6dMHP7U=
+github.com/tyler-smith/go-bip39 v1.1.0 h1:5eUemwrMargf3BSLRRCalXT93Ns6pQJIjYQN2nyfOP8=
+github.com/tyler-smith/go-bip39 v1.1.0/go.mod h1:gUYDtqQw1JS3ZJ8UWVcGTGqqr6YIN3CWg+kkNaLt55U=
 github.com/urfave/cli/v2 v2.25.7 h1:VAzn5oq403l5pHjc4OhD54+XGO9cdKVL/7lDjF+iKUs=
 github.com/urfave/cli/v2 v2.25.7/go.mod h1:8qnjx1vcq5s2/wpsqoZFndg2CE5tNFyrTvS6SinrnYQ=
 github.com/xeipuuv/gojsonpointer v0.0.0-20180127040702-4e3ac2762d5f/go.mod h1:N2zxlSyiKSe5eX1tZViRH5QA0qijqEDrYZiPEAiq3wU=