Added function to generate vkey from skey

note/note_verifier.go

@@ -17,17 +17,64 @@ package note
 
 import (
 	"crypto/ecdsa"
+	"crypto/ed25519"
 	"crypto/sha256"
 	"crypto/x509"
 	"encoding/base64"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"strconv"
 	"strings"
 
 	"golang.org/x/mod/sumdb/note"
 )
 
+// SignerVerifierFromEd25519Key returns a note Signer and Verifier given an
+// Ed25519 private key in the standard note-formatted form, e.g.
+// `PRIVATE+KEY+logandmap+38581672+AXJ0FKWOcO2ch6WC8kP705Ed3Gxu7pVtZLhfHAQwp+FE`.
+func SignerVerifierFromEd25519Key(skey string) (note.Signer, note.Verifier, error) {
+	const algEd25519 = 1
+	s, err := note.NewSigner(skey)
+	if err != nil {
+		return nil, nil, err
+	}
+	parts := strings.SplitN(skey, "+", 5)
+	if n := len(parts); n != 5 {
+		return nil, nil, fmt.Errorf("expected 5 parts but got %d", n)
+	}
+	if parts[0] != "PRIVATE" || parts[1] != "KEY" {
+		return nil, nil, fmt.Errorf("expected first tokens to be [PRIVATE, KEY]")
+	}
+	key, err := base64.StdEncoding.DecodeString(parts[4])
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to decode base64: %v", err)
+	}
+
+	alg, key := key[0], key[1:]
+	switch alg {
+	default:
+		return nil, nil, errors.New("unsupported algorithm")
+
+	case algEd25519:
+		if len(key) != ed25519.SeedSize {
+			return nil, nil, fmt.Errorf("expected key seed of size %d but got %d", ed25519.SeedSize, len(key))
+		}
+		key := ed25519.NewKeyFromSeed(key)
+		publicKey := key.Public().(ed25519.PublicKey)
+		vkey, err := note.NewEd25519VerifierKey(s.Name(), publicKey)
+		if err != nil {
+			return nil, nil, fmt.Errorf("failed to generate verifier from key: %v", err)
+
+		}
+		v, err := note.NewVerifier(vkey)
+		if err != nil {
+			return nil, nil, fmt.Errorf("failed to create verifier from vkey: %v", err)
+		}
+		return s, v, err
+	}
+}
+
 // NewVerifier returns a verifier for the given key, if the key's algo is known.
 func NewVerifier(key string) (note.Verifier, error) {
 	parts := strings.SplitN(key, "+", 3)

note/note_verifier_test.go

@@ -33,6 +33,42 @@ const (
 	pixelKey         = "pixel6_transparency_log" + "+" + pixelKeyHash + "+" + pixelKeyMaterial
 )
 
+func TestSignerVerifierFromEd25519Key(t *testing.T) {
+	for _, test := range []struct {
+		name    string
+		key     string
+		wantErr bool
+	}{
+		{
+			name: "Ed25519 private key",
+			key:  "PRIVATE+KEY+logandmap+38581672+AXJ0FKWOcO2ch6WC8kP705Ed3Gxu7pVtZLhfHAQwp+FE",
+		},
+		{
+			name:    "Ed25519 public key",
+			key:     "logandmap+38581672+Ab/PCr1eCclRPRMBqw/r5An1xO71MCnImLiospEq6b4l",
+			wantErr: true,
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			s, v, err := SignerVerifierFromEd25519Key(test.key)
+			if gotErr := err != nil; gotErr != test.wantErr {
+				t.Fatalf("NewVerifier: %v, wantErr %t", err, test.wantErr)
+			}
+			if test.wantErr {
+				return
+			}
+			msg := []byte("hello")
+			sig, err := s.Sign(msg)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if !v.Verify(msg, sig) {
+				t.Fatal("Failed to verify signature from signer")
+			}
+		})
+	}
+}
+
 func TestNewVerifier(t *testing.T) {
 	for _, test := range []struct {
 		name    string