2 files changed, 280 insertions, 0 deletions
diff --git a/internal/profile/vault.go b/internal/profile/vault.go
new file mode 100644
index 0000000..554d01b
--- /dev/null
+++ b/internal/profile/vault.go
@@ -0,0 +1,235 @@
+// Package profile stores the optional VFace identity in an age-encrypted vault.
+package profile
+
+import (
+	"bytes"
+	"crypto/ed25519"
+	"crypto/rand"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"aegis/internal/cryptokit"
+	"filippo.io/age"
+	agearmor "filippo.io/age/armor"
+)
+
+const (
+	Version           = 1
+	MinPasswordLength = 12
+	maxVaultBytes     = 1 << 20
+)
+
+type Profile struct {
+	Version            int       `json:"version"`
+	Username           string    `json:"username"`
+	Email              string    `json:"email"`
+	PublicKey          string    `json:"ed25519_public_key"`
+	PrivateKey         string    `json:"ed25519_private_key"`
+	AgeIdentity        string    `json:"age_identity,omitempty"`
+	YubiKeyFingerprint string    `json:"yubikey_openpgp_fingerprint,omitempty"`
+	CreatedAt          time.Time `json:"created_at"`
+}
+
+func DefaultPath() (string, error) {
+	directory, err := os.UserConfigDir()
+	if err != nil {
+		return "", fmt.Errorf("locate profile directory: %w", err)
+	}
+	return filepath.Join(directory, "aegis", "profile.json.age"), nil
+}
+
+func Generate(username, email string) (Profile, error) {
+	username = strings.TrimSpace(username)
+	email = strings.TrimSpace(email)
+	if username == "" || email == "" {
+		return Profile{}, errors.New("VFace username and email are required")
+	}
+	if strings.ContainsAny(username+email, "\x00\r\n|") {
+		return Profile{}, errors.New("VFace username and email contain forbidden characters")
+	}
+	publicKey, privateKey, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		return Profile{}, fmt.Errorf("generate VFace Ed25519 key pair: %w", err)
+	}
+	return Profile{
+		Version:    Version,
+		Username:   username,
+		Email:      email,
+		PublicKey:  base64.StdEncoding.EncodeToString(publicKey),
+		PrivateKey: base64.StdEncoding.EncodeToString(privateKey),
+		CreatedAt:  time.Now().UTC(),
+	}, nil
+}
+
+func Save(path string, value Profile, password string) error {
+	if err := validatePassword(password); err != nil {
+		return err
+	}
+	if err := Validate(value); err != nil {
+		return err
+	}
+	plaintext, err := json.MarshalIndent(value, "", "  ")
+	if err != nil {
+		return fmt.Errorf("encode VFace profile: %w", err)
+	}
+	recipient, err := age.NewScryptRecipient(password)
+	if err != nil {
+		return fmt.Errorf("create profile password recipient: %w", err)
+	}
+	var encrypted bytes.Buffer
+	armor := agearmor.NewWriter(&encrypted)
+	writer, err := age.Encrypt(armor, recipient)
+	if err != nil {
+		_ = armor.Close()
+		return fmt.Errorf("create profile vault: %w", err)
+	}
+	if _, err := writer.Write(plaintext); err != nil {
+		_ = writer.Close()
+		_ = armor.Close()
+		return fmt.Errorf("write profile vault: %w", err)
+	}
+	if err := writer.Close(); err != nil {
+		_ = armor.Close()
+		return fmt.Errorf("close profile vault: %w", err)
+	}
+	if err := armor.Close(); err != nil {
+		return fmt.Errorf("close profile armor: %w", err)
+	}
+	return atomicWrite(path, encrypted.Bytes())
+}
+
+func Load(path string, password string) (Profile, error) {
+	if err := validatePassword(password); err != nil {
+		return Profile{}, err
+	}
+	ciphertext, err := os.ReadFile(path)
+	if err != nil {
+		return Profile{}, fmt.Errorf("read profile vault: %w", err)
+	}
+	if len(ciphertext) > maxVaultBytes {
+		return Profile{}, errors.New("profile vault is too large")
+	}
+	identity, err := age.NewScryptIdentity(password)
+	if err != nil {
+		return Profile{}, fmt.Errorf("create profile password identity: %w", err)
+	}
+	reader, err := age.Decrypt(agearmor.NewReader(bytes.NewReader(ciphertext)), identity)
+	if err != nil {
+		return Profile{}, errors.New("cannot unlock profile vault")
+	}
+	plaintext, err := io.ReadAll(io.LimitReader(reader, maxVaultBytes+1))
+	if err != nil {
+		return Profile{}, fmt.Errorf("read profile vault: %w", err)
+	}
+	if len(plaintext) > maxVaultBytes {
+		return Profile{}, errors.New("profile vault contents are too large")
+	}
+	var value Profile
+	if err := json.Unmarshal(plaintext, &value); err != nil {
+		return Profile{}, errors.New("profile vault contains invalid data")
+	}
+	if err := Validate(value); err != nil {
+		return Profile{}, fmt.Errorf("validate profile vault: %w", err)
+	}
+	return value, nil
+}
+
+func Validate(value Profile) error {
+	if value.Version != Version {
+		return fmt.Errorf("unsupported VFace profile version %d", value.Version)
+	}
+	if value.Username == "" || value.Email == "" || strings.ContainsAny(value.Username+value.Email, "\x00\r\n|") {
+		return errors.New("invalid VFace username or email")
+	}
+	publicKey, err := decodePublicKey(value.PublicKey)
+	if err != nil {
+		return err
+	}
+	if strings.TrimSpace(value.PrivateKey) == "" {
+		if strings.TrimSpace(value.YubiKeyFingerprint) == "" {
+			return errors.New("profile needs an encrypted private key or a YubiKey OpenPGP fingerprint")
+		}
+		return nil
+	}
+	privateKey, err := decodePrivateKey(value.PrivateKey)
+	if err != nil {
+		return err
+	}
+	derived := privateKey.Public().(ed25519.PublicKey)
+	if !bytes.Equal(publicKey, derived) {
+		return errors.New("VFace public and private keys do not match")
+	}
+	return nil
+}
+
+func validatePassword(password string) error {
+	if len([]rune(password)) < MinPasswordLength {
+		return fmt.Errorf("profile password must contain at least %d characters", MinPasswordLength)
+	}
+	return nil
+}
+
+func decodePublicKey(value string) (ed25519.PublicKey, error) {
+	canonical, err := cryptokit.CanonicalEd25519PublicKey(value)
+	if err != nil {
+		return nil, fmt.Errorf("invalid VFace public key: %w", err)
+	}
+	decoded, err := base64.StdEncoding.DecodeString(canonical)
+	if err != nil {
+		return nil, errors.New("invalid VFace public key encoding")
+	}
+	return ed25519.PublicKey(decoded), nil
+}
+
+func decodePrivateKey(value string) (ed25519.PrivateKey, error) {
+	decoded, err := base64.StdEncoding.DecodeString(strings.TrimSpace(value))
+	if err != nil || len(decoded) != ed25519.PrivateKeySize {
+		return nil, errors.New("invalid VFace private key")
+	}
+	return ed25519.PrivateKey(decoded), nil
+}
+
+func atomicWrite(path string, data []byte) error {
+	if path == "" {
+		return errors.New("profile vault path is required")
+	}
+	directory := filepath.Dir(path)
+	if err := os.MkdirAll(directory, 0o700); err != nil {
+		return fmt.Errorf("create profile directory: %w", err)
+	}
+	if err := os.Chmod(directory, 0o700); err != nil {
+		return fmt.Errorf("protect profile directory: %w", err)
+	}
+	temporary, err := os.CreateTemp(directory, ".profile-*.tmp")
+	if err != nil {
+		return fmt.Errorf("create profile temporary file: %w", err)
+	}
+	temporaryName := temporary.Name()
+	defer os.Remove(temporaryName)
+	if err := temporary.Chmod(0o600); err != nil {
+		_ = temporary.Close()
+		return err
+	}
+	if _, err := temporary.Write(data); err != nil {
+		_ = temporary.Close()
+		return fmt.Errorf("write profile vault: %w", err)
+	}
+	if err := temporary.Sync(); err != nil {
+		_ = temporary.Close()
+		return fmt.Errorf("sync profile vault: %w", err)
+	}
+	if err := temporary.Close(); err != nil {
+		return err
+	}
+	if err := os.Rename(temporaryName, path); err != nil {
+		return fmt.Errorf("commit profile vault: %w", err)
+	}
+	return nil
+}
diff --git a/internal/profile/vault_test.go b/internal/profile/vault_test.go
new file mode 100644
index 0000000..a726c5f
--- /dev/null
+++ b/internal/profile/vault_test.go
@@ -0,0 +1,45 @@
+package profile
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestVaultRoundTrip(t *testing.T) {
+	value, err := Generate("pseudonym", "reader@example.org")
+	if err != nil {
+		t.Fatal(err)
+	}
+	path := filepath.Join(t.TempDir(), "profile.json.age")
+	if err := Save(path, value, "correct horse battery staple"); err != nil {
+		t.Fatal(err)
+	}
+	loaded, err := Load(path, "correct horse battery staple")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if loaded.Username != value.Username || loaded.PublicKey != value.PublicKey || loaded.PrivateKey != value.PrivateKey {
+		t.Fatal("profile vault round-trip changed identity")
+	}
+	if _, err := Load(path, "wrong password"); err == nil {
+		t.Fatal("wrong password unlocked profile vault")
+	}
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(data) == 0 || string(data) == "" {
+		t.Fatal("empty profile vault")
+	}
+}
+
+func TestPasswordMinimum(t *testing.T) {
+	value, err := Generate("pseudonym", "reader@example.org")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := Save(filepath.Join(t.TempDir(), "profile.json.age"), value, "short"); err == nil {
+		t.Fatal("short profile password accepted")
+	}
+}