feat: share env files as encrypted links

S → f on a repo, an env file or a key in one copies a
lazysecrets://share link holding the env files, encrypted (age) with
a secret's value: whoever can read that secret can open it. The key is
share.key in the repo's .lazysecrets.yaml, else in the config, else
picked when sharing; on Azure the link pins its version. Opening one
says what it holds, decrypts when asked, and saves the files in the
clone of the repo (or a folder chosen), replacing existing ones only
when asked. lazysecrets share prints a link from the command line.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/share/share.go

@@ -0,0 +1,271 @@
+// Package share seals env files into a lazysecrets://share link, so they
+// can be passed on in chat or a ticket. They're encrypted with the value of
+// a secret (in Key Vault, Databricks or a repo's SOPS file): whoever can
+// read that secret can open the link, nobody else.
+//
+// A link says in the clear which secret it's encrypted with, the repo the
+// files are from and how many there are, which is what's needed to open
+// it. The files' paths and contents are encrypted, with age
+// (https://age-encryption.org), the secret's value as its passphrase.
+//
+// The link's payload is unpadded base64url of:
+//
+//	version (1) | uvarint length of the header | header (JSON) | age file
+//
+// The age file holds the files as deflated JSON.
+package share
+
+import (
+	"bytes"
+	"compress/flate"
+	"encoding/base64"
+	"encoding/binary"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"path"
+	"strings"
+	"unicode/utf8"
+
+	"filippo.io/age"
+
+	"git.kebcloud.no/keb/lazysecrets/internal/provider"
+	"git.kebcloud.no/keb/lazysecrets/internal/provider/repo"
+	"git.kebcloud.no/keb/lazysecrets/internal/ref"
+)
+
+const (
+	version = 1
+	// MaxLink keeps a link short enough for chat and tickets (Teams takes
+	// about 28 KB) and for passing it to a terminal window.
+	MaxLink = 16 << 10
+	// MinKey is the shortest secret value accepted as a key.
+	MinKey = 16
+	// maxFiles caps what opening a link unpacks.
+	maxFiles = 1 << 20
+)
+
+// workFactor is age's scrypt work factor for sealing (its default);
+// maxWorkFactor is the most opening accepts, so a link can't make it
+// work for minutes.
+var workFactor, maxWorkFactor = 18, 20
+
+// File is a shared file.
+type File struct {
+	Path string // relative to the repo's root, with slashes
+	Data []byte
+}
+
+// Header is what a link says in the clear.
+type Header struct {
+	// Key is the secret whose value the files are encrypted with.
+	Key ref.Ref
+	// Repo is the repo the files are from: its remote without scheme or
+	// .git (a repo link's host).
+	Repo string
+	// Files is how many files the link holds.
+	Files int
+}
+
+// Sealed is a share link read, its files still encrypted.
+type Sealed struct {
+	Header
+	box []byte
+}
+
+type header struct {
+	Key   string `json:"key"`
+	Repo  string `json:"repo,omitempty"`
+	Files int    `json:"files"`
+}
+
+type file struct {
+	Path string `json:"path"`
+	Data string `json:"data"`
+}
+
+// Seal encrypts files with key, the value of h.Key, into a share link.
+func Seal(h Header, key []byte, files []File) (ref.Ref, error) {
+	if h.Key.IsShare() || h.Key.IsSource() || h.Key.IsContainer() {
+		return ref.Ref{}, errors.New("the key must be a secret's link")
+	}
+	if len(key) < MinKey {
+		return ref.Ref{}, fmt.Errorf("the key's value is %d characters: use a random one of at least %d", len(key), MinKey)
+	}
+	if len(files) == 0 {
+		return ref.Ref{}, errors.New("no files to share")
+	}
+	plain := make([]file, len(files))
+	for i, f := range files {
+		if err := CheckPath(f.Path); err != nil {
+			return ref.Ref{}, err
+		}
+		if !utf8.Valid(f.Data) {
+			return ref.Ref{}, fmt.Errorf("%s isn't text", f.Path)
+		}
+		plain[i] = file{Path: f.Path, Data: string(f.Data)}
+	}
+	b, err := json.Marshal(plain)
+	if err != nil {
+		return ref.Ref{}, err
+	}
+
+	rcpt, err := age.NewScryptRecipient(string(key))
+	if err != nil {
+		return ref.Ref{}, err
+	}
+	rcpt.SetWorkFactor(workFactor)
+	var box bytes.Buffer
+	enc, err := age.Encrypt(&box, rcpt)
+	if err != nil {
+		return ref.Ref{}, err
+	}
+	z, _ := flate.NewWriter(enc, flate.BestCompression)
+	if _, err := z.Write(b); err != nil {
+		return ref.Ref{}, err
+	}
+	if err := z.Close(); err != nil {
+		return ref.Ref{}, err
+	}
+	if err := enc.Close(); err != nil {
+		return ref.Ref{}, err
+	}
+
+	hb, err := json.Marshal(header{Key: h.Key.String(), Repo: h.Repo, Files: len(files)})
+	if err != nil {
+		return ref.Ref{}, err
+	}
+	payload := binary.AppendUvarint([]byte{version}, uint64(len(hb)))
+	payload = append(append(payload, hb...), box.Bytes()...)
+	r := ref.Ref{Share: base64.RawURLEncoding.EncodeToString(payload)}
+	if n := len(r.String()); n > MaxLink {
+		return ref.Ref{}, fmt.Errorf("the link would be %d KB, more than the %d KB it can be: share fewer files", n>>10, MaxLink>>10)
+	}
+	return r, nil
+}
+
+// Read reads a share link's header.
+func Read(r ref.Ref) (Sealed, error) {
+	bad := errors.New("share link is cut short or garbled: copy all of it")
+	b, err := base64.RawURLEncoding.DecodeString(r.Share)
+	if err != nil || len(b) < 2 {
+		return Sealed{}, bad
+	}
+	if b[0] != version {
+		return Sealed{}, errors.New("share link is from a newer lazysecrets: update it (lazysecrets update)")
+	}
+	n, size := binary.Uvarint(b[1:])
+	if size <= 0 || n > uint64(len(b)) {
+		return Sealed{}, bad
+	}
+	rest := b[1+size:]
+	if n > uint64(len(rest)) {
+		return Sealed{}, bad
+	}
+	var h header
+	if err := json.Unmarshal(rest[:n], &h); err != nil {
+		return Sealed{}, bad
+	}
+	key, err := ParseKey(h.Key)
+	if err != nil {
+		return Sealed{}, fmt.Errorf("share link's key: %w", err)
+	}
+	return Sealed{Header: Header{Key: key, Repo: h.Repo, Files: h.Files}, box: rest[n:]}, nil
+}
+
+// Open decrypts the files with key, the value of s.Key.
+func (s Sealed) Open(key []byte) ([]File, error) {
+	id, err := age.NewScryptIdentity(string(key))
+	if err != nil {
+		return nil, err
+	}
+	id.SetMaxWorkFactor(maxWorkFactor)
+	dec, err := age.Decrypt(bytes.NewReader(s.box), id)
+	if err != nil {
+		var wrong *age.NoIdentityMatchError
+		if errors.As(err, &wrong) {
+			return nil, errors.New("the key doesn't decrypt it: the link may have been made with another version of " + s.Key.Name)
+		}
+		return nil, fmt.Errorf("can't decrypt the link: %w", err)
+	}
+	b, err := io.ReadAll(io.LimitReader(flate.NewReader(dec), maxFiles+1))
+	if err != nil {
+		return nil, fmt.Errorf("can't decrypt the link: %w", err)
+	}
+	if len(b) > maxFiles {
+		return nil, errors.New("the link holds more than lazysecrets unpacks")
+	}
+	var plain []file
+	if err := json.Unmarshal(b, &plain); err != nil {
+		return nil, fmt.Errorf("can't read the link's files: %w", err)
+	}
+	out := make([]File, len(plain))
+	for i, f := range plain {
+		if err := CheckPath(f.Path); err != nil {
+			return nil, err
+		}
+		out[i] = File{Path: f.Path, Data: []byte(f.Data)}
+	}
+	return out, nil
+}
+
+// CheckPath accepts a path relative to a repo's root, with slashes, of an
+// env file (.env, .env.local, prod.env) outside .git: what a link may
+// write.
+func CheckPath(p string) error {
+	switch {
+	case p == "" || path.IsAbs(p) || strings.ContainsAny(p, "\\\x00") || path.Clean(p) != p ||
+		p == ".." || strings.HasPrefix(p, "../"):
+		return fmt.Errorf("%q isn't a path inside a repo", p)
+	case p == ".git" || strings.HasPrefix(p, ".git/") || strings.Contains(p, "/.git/"):
+		return fmt.Errorf("%q is inside .git", p)
+	case !repo.IsEnv(p):
+		return fmt.Errorf("%q isn't an env file: only those can be shared", p)
+	}
+	return nil
+}
+
+// DefaultKey is the key for a repo's files: share.key in the repo's
+// .lazysecrets.yaml, else general (share.key in the config). ok is false
+// when neither names one.
+func DefaultKey(root, general string) (key ref.Ref, ok bool, err error) {
+	link, err := repo.ShareKey(root)
+	if err != nil {
+		return ref.Ref{}, false, err
+	}
+	where := root + "/.lazysecrets.yaml"
+	if link == "" {
+		link, where = general, "the config"
+	}
+	if link == "" {
+		return ref.Ref{}, false, nil
+	}
+	key, err = ParseKey(link)
+	if err != nil {
+		return ref.Ref{}, false, fmt.Errorf("share.key in %s: %w", where, err)
+	}
+	return key, true, nil
+}
+
+// ParseKey reads a key's link: a link to a secret.
+func ParseKey(link string) (ref.Ref, error) {
+	key, err := ref.Parse(link)
+	if err != nil {
+		return ref.Ref{}, err
+	}
+	if key.IsShare() || key.IsSource() || key.IsContainer() {
+		return ref.Ref{}, fmt.Errorf("%s isn't a secret's link", link)
+	}
+	return key, nil
+}
+
+// Pin is key at version, the version its value was read at, for Azure,
+// whose old versions stay readable: a link keeps working when the key
+// is rotated, until that version is disabled.
+func Pin(key ref.Ref, version string) ref.Ref {
+	if key.Kind == provider.KindAzure && key.Version == "" {
+		key.Version = version
+	}
+	return key
+}

internal/share/share_test.go

@@ -0,0 +1,190 @@
+package share
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.kebcloud.no/keb/lazysecrets/internal/provider"
+	"git.kebcloud.no/keb/lazysecrets/internal/ref"
+)
+
+func init() { workFactor = 10 } // fast; opening accepts any up to maxWorkFactor
+
+var (
+	key  = ref.Ref{Kind: provider.KindAzure, Host: "kv-team.vault.azure.net", Type: provider.TypeSecret, Name: "env-share", Version: "91d3e0"}
+	pass = []byte("0123456789abcdef0123456789abcdef")
+)
+
+func TestSealOpen(t *testing.T) {
+	files := []File{
+		{Path: ".env", Data: []byte("DB_PASSWORD=hunter2\n")},
+		{Path: "apps/api/.env.local", Data: []byte("TOKEN=\"a b\" # quoted\n")},
+	}
+	link, err := Seal(Header{Key: key, Repo: "git.example.com/team/app"}, pass, files)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.Contains(link.String(), "hunter2") || strings.Contains(link.String(), "apps") {
+		t.Errorf("link shows what it shares: %s", link)
+	}
+	// It goes through ref.Parse like any link.
+	r, err := ref.Parse(link.String())
+	if err != nil || !r.IsShare() {
+		t.Fatalf("parse: %v, %+v", err, r)
+	}
+	s, err := Read(r)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if s.Key != key || s.Repo != "git.example.com/team/app" || s.Files != 2 {
+		t.Errorf("header %+v", s.Header)
+	}
+	got, err := s.Open(pass)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(got) != 2 || got[1].Path != files[1].Path || string(got[1].Data) != string(files[1].Data) {
+		t.Errorf("opened %+v", got)
+	}
+	if _, err := s.Open([]byte("another key, long enough to use")); err == nil || !strings.Contains(err.Error(), "doesn't decrypt") {
+		t.Errorf("wrong key: %v", err)
+	}
+}
+
+func TestSealRefuses(t *testing.T) {
+	ok := []File{{Path: ".env", Data: []byte("A=1")}}
+	for name, c := range map[string]struct {
+		h     Header
+		pass  []byte
+		files []File
+		want  string
+	}{
+		"short key":    {Header{Key: key}, []byte("short"), ok, "at least 16"},
+		"vault as key": {Header{Key: ref.Ref{Kind: provider.KindAzure, Host: "kv.vault.azure.net"}}, pass, ok, "secret's link"},
+		"no files":     {Header{Key: key}, pass, nil, "no files"},
+		"not env":      {Header{Key: key}, pass, []File{{Path: "main.go", Data: []byte("x")}}, "isn't an env file"},
+		"escapes":      {Header{Key: key}, pass, []File{{Path: "../.env", Data: []byte("x")}}, "inside a repo"},
+		"binary":       {Header{Key: key}, pass, []File{{Path: ".env", Data: []byte{0xff, 0xfe}}}, "isn't text"},
+		"too big":      {Header{Key: key}, pass, []File{{Path: ".env", Data: []byte(random(2 * MaxLink))}}, "more than the 16 KB"},
+	} {
+		if _, err := Seal(c.h, c.pass, c.files); err == nil || !strings.Contains(err.Error(), c.want) {
+			t.Errorf("%s: %v, want %q", name, err, c.want)
+		}
+	}
+}
+
+// random is text that doesn't compress.
+func random(n int) string {
+	var b strings.Builder
+	x := uint32(1)
+	for b.Len() < n {
+		x ^= x << 13
+		x ^= x >> 17
+		x ^= x << 5
+		b.WriteByte("abcdefghijklmnopqrstuvwxyz0123456789"[x%36])
+	}
+	return b.String()
+}
+
+func TestReadGarbled(t *testing.T) {
+	link, err := Seal(Header{Key: key}, pass, []File{{Path: ".env", Data: []byte("A=1")}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	cut := ref.Ref{Share: link.Share[:len(link.Share)/2]}
+	s, err := Read(cut)
+	if err == nil {
+		_, err = s.Open(pass)
+	}
+	if err == nil {
+		t.Error("a link cut in half opened")
+	}
+	if _, err := Read(ref.Ref{Share: "AgAAAAAAAAAAAAAAAAAAAA"}); err == nil || !strings.Contains(err.Error(), "newer lazysecrets") {
+		t.Errorf("version 2: %v", err)
+	}
+}
+
+func TestCheckPath(t *testing.T) {
+	for _, p := range []string{".env", "apps/api/.env.local", "prod.env"} {
+		if err := CheckPath(p); err != nil {
+			t.Errorf("%s: %v", p, err)
+		}
+	}
+	for _, p := range []string{"", "/etc/.env", "../.env", "a/../.env", ".git/.env", "a/.git/x.env", `a\.env`, ".env.example", "node_modules/x/.env", "Makefile"} {
+		if err := CheckPath(p); err == nil {
+			t.Errorf("%q accepted", p)
+		}
+	}
+}
+
+func TestPlanWrite(t *testing.T) {
+	dir := t.TempDir()
+	if out, err := exec.Command("git", "-C", dir, "init", "-q").CombinedOutput(); err != nil {
+		t.Skip("git:", string(out))
+	}
+	os.WriteFile(filepath.Join(dir, ".gitignore"), []byte(".env\n"), 0o644)
+	os.WriteFile(filepath.Join(dir, ".env"), []byte("OLD=1\n"), 0o644)
+	targets, err := Plan(dir, []File{
+		{Path: ".env", Data: []byte("NEW=1\n")},
+		{Path: "apps/api/.env.local", Data: []byte("B=2\n")},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !targets[0].Exists || targets[0].Exposed {
+		t.Errorf(".env: %+v", targets[0])
+	}
+	if targets[1].Exists || !targets[1].Exposed {
+		t.Errorf("apps/api/.env.local: %+v", targets[1])
+	}
+	for _, tg := range targets {
+		if err := tg.Write(); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if b, _ := os.ReadFile(filepath.Join(dir, ".env")); string(b) != "NEW=1\n" {
+		t.Errorf(".env is %q", b)
+	}
+	info, err := os.Stat(filepath.Join(dir, "apps", "api", ".env.local"))
+	if err != nil || info.Mode().Perm() != 0o600 {
+		t.Errorf("new file: %v, %v", info.Mode(), err)
+	}
+}
+
+func TestPlanSymlinks(t *testing.T) {
+	dir, outside := t.TempDir(), t.TempDir()
+	if err := os.Symlink(outside, filepath.Join(dir, "apps")); err != nil {
+		t.Skip(err)
+	}
+	if _, err := Plan(dir, []File{{Path: "apps/.env"}}); err == nil || !strings.Contains(err.Error(), "out of the folder") {
+		t.Errorf("through a linked folder: %v", err)
+	}
+	os.Symlink(filepath.Join(outside, "x"), filepath.Join(dir, ".env"))
+	if _, err := Plan(dir, []File{{Path: ".env"}}); err == nil || !strings.Contains(err.Error(), "symlink") {
+		t.Errorf("onto a symlink: %v", err)
+	}
+}
+
+func TestDefaultKey(t *testing.T) {
+	dir := t.TempDir()
+	general := "lazysecrets://azure/kv-team.vault.azure.net/secrets/env-share"
+	k, ok, err := DefaultKey(dir, general)
+	if err != nil || !ok || k.Name != "env-share" {
+		t.Errorf("general: %+v %v %v", k, ok, err)
+	}
+	os.WriteFile(filepath.Join(dir, ".lazysecrets.yaml"), []byte("share:\n  key: lazysecrets://azure/kv-app.vault.azure.net/secrets/app-share\n"), 0o644)
+	if k, _, _ := DefaultKey(dir, general); k.Name != "app-share" {
+		t.Errorf("the repo's should win: %+v", k)
+	}
+	if _, ok, _ := DefaultKey(t.TempDir(), ""); ok {
+		t.Error("a key with none set")
+	}
+	unpinned := key
+	unpinned.Version = ""
+	if p := Pin(unpinned, "abc"); p.Version != "abc" {
+		t.Errorf("pin: %+v", p)
+	}
+}

internal/share/write.go

@@ -0,0 +1,87 @@
+package share
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+// Target is where an opened file goes.
+type Target struct {
+	File
+	Abs    string
+	Exists bool
+	// Exposed is set when dir is a git repo that doesn't ignore the file:
+	// its values could end up in a commit.
+	Exposed bool
+}
+
+// Plan says where files go under dir, without writing anything. A path
+// that leads out of dir through a symlink, or is one, is an error.
+func Plan(dir string, files []File) ([]Target, error) {
+	root, err := filepath.EvalSymlinks(dir)
+	if err != nil {
+		return nil, err
+	}
+	out := make([]Target, len(files))
+	for i, f := range files {
+		if err := CheckPath(f.Path); err != nil {
+			return nil, err
+		}
+		t := Target{File: f, Abs: filepath.Join(root, filepath.FromSlash(f.Path))}
+		if err := inside(root, filepath.Dir(t.Abs)); err != nil {
+			return nil, fmt.Errorf("%s: %w", f.Path, err)
+		}
+		switch info, err := os.Lstat(t.Abs); {
+		case err == nil && info.Mode()&fs.ModeSymlink != 0:
+			return nil, fmt.Errorf("%s is a symlink: not writing through it", f.Path)
+		case err == nil && !info.Mode().IsRegular():
+			return nil, fmt.Errorf("%s isn't a file", f.Path)
+		case err == nil:
+			t.Exists = true
+		case !errors.Is(err, fs.ErrNotExist):
+			return nil, err
+		}
+		t.Exposed = exposed(root, f.Path)
+		out[i] = t
+	}
+	return out, nil
+}
+
+// inside checks that dir, or the part of it that exists, is under root
+// once symlinks are followed.
+func inside(root, dir string) error {
+	for {
+		real, err := filepath.EvalSymlinks(dir)
+		if errors.Is(err, fs.ErrNotExist) && dir != root {
+			dir = filepath.Dir(dir) // created when writing
+			continue
+		}
+		if err != nil {
+			return err
+		}
+		if real != root && !strings.HasPrefix(real, root+string(filepath.Separator)) {
+			return errors.New("leads out of the folder through a symlink")
+		}
+		return nil
+	}
+}
+
+// exposed reports whether root is in a git repo that doesn't ignore p.
+func exposed(root, p string) bool {
+	err := exec.Command("git", "-C", root, "check-ignore", "-q", "--", p).Run()
+	var exit *exec.ExitError
+	return errors.As(err, &exit) && exit.ExitCode() == 1 // 0: ignored; 128: no repo
+}
+
+// Write writes the file, readable by the user only when it's new.
+func (t Target) Write() error {
+	if err := os.MkdirAll(filepath.Dir(t.Abs), 0o755); err != nil {
+		return err
+	}
+	return os.WriteFile(t.Abs, t.Data, 0o600)
+}