Sign and verify manifests in Go with OpenPGP instead of running gpg (closes #181)

mfer ran the gpg binary to sign, export keys and verify, so signing and
loading signed manifests failed wherever gpg is missing. It now uses
github.com/ProtonMail/go-crypto/openpgp. --sign-key and MFER_SIGN_KEY
name a file holding one version 4 OpenPGP secret key; a protected key's
passphrase comes from MFER_SIGN_KEY_PASSPHRASE or a terminal prompt. gen
and freshen check that the key can sign before they read any file.
Verification keeps the rules of the --require-signature fix: one primary
key in the embedded block, counted from its packets, exactly one
signature, made by that key or a subkey, and signer equal to its
fingerprint. A DSA key is refused, and so is an armored field that is
not one well-formed block.

Model: opus-5-5

internal/cli/signing_test.go

@@ -0,0 +1,209 @@
+//nolint:testpackage // white-box tests exercise unexported internals
+package cli
+
+import (
+	"bufio"
+	"io"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/ProtonMail/go-crypto/openpgp/packet"
+	"github.com/creack/pty"
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+const (
+	testFlagSignKey = "--sign-key"
+	testKeyFile     = "/key.asc"
+)
+
+// TestGenAndFreshenSignWithKeyFile runs gen, then freshen after a file is
+// added, with --sign-key naming a key file: one key with no passphrase and
+// one protected by the passphrase in MFER_SIGN_KEY_PASSPHRASE. check
+// --require-signature must accept each manifest as signed by that key.
+// freshen leaves its manifest out of the listing only on the real
+// filesystem, so the test uses that.
+func TestGenAndFreshenSignWithKeyFile(t *testing.T) {
+	for name, passphrase := range map[string][]byte{
+		"unprotected": nil,
+		"protected":   []byte("passphrase"),
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Setenv(envSignKeyPassphrase, string(passphrase))
+
+			secretKey, fingerprint := testSecretKey(t, passphrase, nil)
+
+			fs := afero.NewOsFs()
+			keyFile := filepath.Join(t.TempDir(), "key.asc")
+			root := t.TempDir()
+			manifestPath := filepath.Join(root, defaultManifestName)
+
+			require.NoError(t, afero.WriteFile(fs, keyFile, secretKey, 0o600))
+			writeTestFile(t, fs, filepath.Join(root, testFileTxt), "hello")
+
+			opts := testOpts([]string{
+				testApp, cmdGenerate, "-q", testFlagSignKey, keyFile,
+				"-o", manifestPath, root,
+			}, fs)
+			require.Equal(t, 0, runCLI(opts), testStderr(t, opts))
+
+			check := []string{
+				testApp, cmdCheck, "-q",
+				"--" + flagRequireSignature, fingerprint, manifestPath,
+			}
+
+			opts = testOpts(check, fs)
+			require.Equal(t, 0, runCLI(opts), testStderr(t, opts))
+
+			writeTestFile(t, fs, filepath.Join(root, "added.txt"), "added")
+
+			opts = testOpts([]string{
+				testApp, cmdFreshen, "-q", testFlagSignKey, keyFile, manifestPath,
+			}, fs)
+			require.Equal(t, 0, runCLI(opts), testStderr(t, opts))
+
+			opts = testOpts(check, fs)
+			require.Equal(t, 0, runCLI(opts), testStderr(t, opts))
+			assert.Len(t, manifestFiles(t, fs, manifestPath), 2)
+		})
+	}
+}
+
+// TestSignWithProtectedKeyNeedsPassphrase runs gen with a protected key,
+// with MFER_SIGN_KEY_PASSPHRASE empty and no terminal to ask on. gen must
+// fail, naming the variable, and write no manifest.
+func TestSignWithProtectedKeyNeedsPassphrase(t *testing.T) {
+	t.Setenv(envSignKeyPassphrase, "")
+
+	secretKey, _ := testSecretKey(t, []byte("secret"), nil)
+
+	fs := afero.NewMemMapFs()
+	require.NoError(t, afero.WriteFile(fs, testKeyFile, secretKey, 0o600))
+	require.NoError(t, fs.MkdirAll(testDir, 0o755))
+	writeTestFile(t, fs, testFile1, "hello")
+
+	opts := testOpts([]string{
+		testApp, cmdGenerate, "-q", testFlagSignKey, testKeyFile,
+		"-o", testMF, testDir,
+	}, fs)
+	assert.Equal(t, 1, runCLI(opts))
+	assert.Contains(t, testStderr(t, opts),
+		"signing key is protected: set MFER_SIGN_KEY_PASSPHRASE to its passphrase")
+
+	exists, err := afero.Exists(fs, testMF)
+	require.NoError(t, err)
+	assert.False(t, exists)
+}
+
+// TestSignWithKeyThatCannotSignFailsFirst runs gen on a directory and
+// freshen on a manifest, neither of which exists, with keys that cannot
+// sign: a protected key with a wrong MFER_SIGN_KEY_PASSPHRASE, a key that
+// expired in 2020, and a version 6 key. Each run must fail on the key: it
+// checks the key before it reads any file, so a missing file goes
+// unnoticed.
+func TestSignWithKeyThatCannotSignFailsFirst(t *testing.T) {
+	t.Setenv(envSignKeyPassphrase, "wrong")
+
+	wrongPassphrase, _ := testSecretKey(t, []byte("right"), nil)
+
+	made := time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC)
+	expired, _ := testSecretKey(t, nil, &packet.Config{
+		Algorithm:       packet.PubKeyAlgoEdDSA,
+		Time:            func() time.Time { return made },
+		KeyLifetimeSecs: uint32((24 * time.Hour).Seconds()),
+	})
+
+	version6, _ := testSecretKey(t, nil, &packet.Config{
+		Algorithm: packet.PubKeyAlgoEd25519,
+		V6Keys:    true,
+	})
+
+	for want, secretKey := range map[string][]byte{
+		"unlock signing key":                           wrongPassphrase,
+		"signing key cannot sign":                      expired,
+		"signing key must be an OpenPGP version 4 key": version6,
+	} {
+		fs := afero.NewMemMapFs()
+		require.NoError(t, afero.WriteFile(fs, testKeyFile, secretKey, 0o600))
+
+		for _, args := range [][]string{
+			{
+				testApp, cmdGenerate, "-q", testFlagSignKey, testKeyFile,
+				"-o", testMF, "/missing",
+			},
+			{testApp, cmdFreshen, "-q", testFlagSignKey, testKeyFile, "/missing.mf"},
+		} {
+			opts := testOpts(args, fs)
+			assert.Equal(t, 1, runCLI(opts), args[1], want)
+			assert.Contains(t, testStderr(t, opts), testKeyFile+": "+want, args[1])
+		}
+	}
+}
+
+// TestGenAsksForPassphraseOnTerminal runs gen with a protected key, no
+// MFER_SIGN_KEY_PASSPHRASE, and a terminal as stdin and stderr. gen must
+// ask for the passphrase on stderr, and sign with what is typed after the
+// prompt.
+func TestGenAsksForPassphraseOnTerminal(t *testing.T) {
+	t.Setenv(envSignKeyPassphrase, "")
+
+	secretKey, fingerprint := testSecretKey(t, []byte("passphrase"), nil)
+
+	fs := afero.NewOsFs()
+	keyFile := filepath.Join(t.TempDir(), "key.asc")
+	root := t.TempDir()
+	manifestPath := filepath.Join(root, defaultManifestName)
+
+	require.NoError(t, afero.WriteFile(fs, keyFile, secretKey, 0o600))
+	writeTestFile(t, fs, filepath.Join(root, testFileTxt), "hello")
+
+	terminal, tty, err := pty.Open()
+	require.NoError(t, err)
+
+	t.Cleanup(func() { _ = terminal.Close() })
+
+	opts := testOpts([]string{
+		testApp, cmdGenerate, "-q", testFlagSignKey, keyFile,
+		"-o", manifestPath, root,
+	}, fs)
+	opts.Stdin = tty
+	opts.Stderr = tty
+
+	exitCode := make(chan int, 1)
+
+	go func() {
+		exitCode <- runCLI(opts)
+
+		// Once gen has ended, reading the terminal fails instead of
+		// waiting for a prompt that will not come.
+		_ = tty.Close()
+	}()
+
+	prompt := "Passphrase for " + keyFile + ": "
+	output := bufio.NewReader(terminal)
+	written := ""
+
+	for !strings.HasSuffix(written, prompt) {
+		b, err := output.ReadByte()
+		require.NoError(t, err, "gen wrote %q and no prompt", written)
+
+		written += string(b)
+	}
+
+	_, err = terminal.WriteString("passphrase\n")
+	require.NoError(t, err)
+
+	code := <-exitCode
+	rest, _ := io.ReadAll(output)
+	require.Equal(t, 0, code, "gen wrote %q", rest)
+
+	check := testOpts([]string{
+		testApp, cmdCheck, "-q",
+		"--" + flagRequireSignature, fingerprint, manifestPath,
+	}, fs)
+	require.Equal(t, 0, runCLI(check), testStderr(t, check))
+}