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 OpenPGP secret key; a protected key's passphrase
comes from MFER_SIGN_KEY_PASSPHRASE or a prompt on the terminal.
Verification keeps the rules of the --require-signature fix: one primary
key in the embedded block, counted from its packets so that keys the
library skips count too, exactly one signature, made by that key or one
of its subkeys, and signer equal to its fingerprint. Tests make their
keys in process.

Model: opus-5-5

go.mod

@@ -4,7 +4,6 @@ go 1.27.1
 
 require (
 	github.com/ProtonMail/go-crypto v1.5.2
-	github.com/creack/pty v1.1.25-0.20260601142114-9246436fffe8
 	github.com/davecgh/go-spew v1.1.1
 	github.com/dustin/go-humanize v1.1.0
 	github.com/klauspost/compress v1.20.1

go.sum

@@ -2,8 +2,6 @@ github.com/ProtonMail/go-crypto v1.5.2 h1:cucYnvqcY7UOXVD//mSyjeaPY0SSN3v5cDkYPx
 github.com/ProtonMail/go-crypto v1.5.2/go.mod h1:/RaSu30DaKO4RY+XdV/ACcCcZkGr7AhUIduq5sjzzCo=
 github.com/cloudflare/circl v1.6.3 h1:9GPOhQGF9MCYUeXyMYlqTR6a5gTrgR/fBLXvUgtVcg8=
 github.com/cloudflare/circl v1.6.3/go.mod h1:2eXP6Qfat4O/Yhh8BznvKnJ+uzEoTQ6jVKJRn81BiS4=
-github.com/creack/pty v1.1.25-0.20260601142114-9246436fffe8 h1:CY3gjC7naqYGLMiywvj3suPfa1i0p/QEr7o8ujxL/2M=
-github.com/creack/pty v1.1.25-0.20260601142114-9246436fffe8/go.mod h1:08sCNb52WyoAwi2QDyzUCTgcvVFhUzewun7wtTfvcwE=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dustin/go-humanize v1.1.0 h1:dbKTrvD0klcbBV/h4AWJdMuZogJACoMlvWIWZ5b2xWg=

internal/cli/errmsg_test.go

@@ -5,11 +5,11 @@ import (
 	"bytes"
 	"context"
 	"encoding/hex"
-	"io"
 	"net/http"
 	"net/http/httptest"
 	"os"
 	"path/filepath"
+	"slices"
 	"strings"
 	"testing"
 
@@ -209,26 +209,10 @@ func manifestSignedByAnotherKey(
 	require.NoError(t, proto.Unmarshal(
 		signedManifest(t, files)[len(mfer.MAGIC):], outer))
 
-	// One armored block holding both keys, as gpg --export --armor writes
+	// Armored blocks start on a line of their own; mfer, unlike gpg, ends
-	// two keys.
+	// one without a newline.
-	var block bytes.Buffer
+	outer.SigningPubKey = slices.Concat(
-
+		required.GetSigningPubKey(), []byte("\n"), outer.GetSigningPubKey())
-	w, err := armor.Encode(&block, openpgp.PublicKeyType, nil)
-	require.NoError(t, err)
-
-	for _, key := range [][]byte{
-		required.GetSigningPubKey(), outer.GetSigningPubKey(),
-	} {
-		decoded, err := armor.Decode(bytes.NewReader(key))
-		require.NoError(t, err)
-
-		_, err = io.Copy(w, decoded.Body)
-		require.NoError(t, err)
-	}
-
-	require.NoError(t, w.Close())
-
-	outer.SigningPubKey = block.Bytes()
 	outer.Signer = required.GetSigner()
 
 	data, err := proto.Marshal(outer)

internal/cli/signing.go

@@ -24,8 +24,7 @@ var errNoPassphrase = errors.New(
 
 // signingOptions returns the signing options for the OpenPGP secret key in
 // the file path. The passphrase of a protected key comes from
-// MFER_SIGN_KEY_PASSPHRASE, or else from the terminal on stdin, and must
+// MFER_SIGN_KEY_PASSPHRASE, or else from the terminal on stdin.
-// unlock the key.
 func (mfa *CLIApp) signingOptions(path string) (*mfer.SigningOptions, error) {
 	secretKey, err := afero.ReadFile(mfa.Fs, path)
 	if err != nil {
@@ -49,13 +48,6 @@ func (mfa *CLIApp) signingOptions(path string) (*mfer.SigningOptions, error) {
 		return nil, err
 	}
 
-	// gen and freshen read the signing options before any file, so a
-	// wrong passphrase stops them before they hash anything.
-	err = mfer.CheckSigningKey(opts)
-	if err != nil {
-		return nil, fmt.Errorf("%s: %w", path, err)
-	}
-
 	return opts, nil
 }
 

internal/cli/signing_test.go

@@ -2,22 +2,15 @@
 package cli
 
 import (
-	"bufio"
-	"io"
 	"path/filepath"
-	"strings"
 	"testing"
 
-	"github.com/creack/pty"
 	"github.com/spf13/afero"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
-const (
+const testFlagSignKey = "--sign-key"
-	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
@@ -80,12 +73,12 @@ func TestSignWithProtectedKeyNeedsPassphrase(t *testing.T) {
 	secretKey, _ := testSecretKey(t, []byte("secret"))
 
 	fs := afero.NewMemMapFs()
-	require.NoError(t, afero.WriteFile(fs, testKeyFile, secretKey, 0o600))
+	require.NoError(t, afero.WriteFile(fs, "/key.asc", secretKey, 0o600))
 	require.NoError(t, fs.MkdirAll(testDir, 0o755))
 	writeTestFile(t, fs, testFile1, "hello")
 
 	opts := testOpts([]string{
-		testApp, cmdGenerate, "-q", testFlagSignKey, testKeyFile,
+		testApp, cmdGenerate, "-q", testFlagSignKey, "/key.asc",
 		"-o", testMF, testDir,
 	}, fs)
 	assert.Equal(t, 1, runCLI(opts))
@@ -96,93 +89,3 @@ func TestSignWithProtectedKeyNeedsPassphrase(t *testing.T) {
 	require.NoError(t, err)
 	assert.False(t, exists)
 }
-
-// TestSignWithWrongPassphraseFailsFirst runs gen on a directory and
-// freshen on a manifest, neither of which exists, with a protected key and
-// a wrong MFER_SIGN_KEY_PASSPHRASE. Each must fail to unlock the key: it
-// does that before it reads any file, so a missing file goes unnoticed.
-func TestSignWithWrongPassphraseFailsFirst(t *testing.T) {
-	t.Setenv(envSignKeyPassphrase, "wrong")
-
-	secretKey, _ := testSecretKey(t, []byte("right"))
-
-	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])
-		assert.Contains(t, testStderr(t, opts),
-			testKeyFile+": unlock signing key", 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"))
-
-	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))
-}

mfer/openpgp.go

@@ -23,10 +23,8 @@ const (
 	secretKeyPacketTag = 5
 	publicKeyPacketTag = 6
 
-	// armorBegin and armorEnd start the lines that begin and end an
+	// armorEnd starts the line that ends an armored block.
-	// armored block.
+	armorEnd = "-----END "
-	armorBegin = "-----BEGIN "
-	armorEnd   = "-----END "
 )
 
 var (
@@ -36,8 +34,6 @@ var (
 		"signing key is protected and no passphrase was given")
 	errNotOneSignature = errors.New(
 		"signature must hold exactly one signature")
-	errNotOneArmoredBlock = errors.New(
-		"must be exactly one armored block and nothing else")
 )
 
 // SigningOptions holds the key a manifest is signed with.
@@ -61,16 +57,6 @@ func SecretKeyIsProtected(secretKey []byte) (bool, error) {
 	return isProtected(key), nil
 }
 
-// CheckSigningKey fails unless opts can sign: opts.SecretKey must hold one
-// primary key with its secret key, and opts.Passphrase must unlock it when
-// it is protected. It lets a caller find a wrong passphrase before it
-// builds a manifest.
-func CheckSigningKey(opts *SigningOptions) error {
-	_, err := readSigningKey(opts)
-
-	return err
-}
-
 // readSigningKey returns the key in opts.SecretKey, unlocked with
 // opts.Passphrase if it is protected.
 func readSigningKey(opts *SigningOptions) (*openpgp.Entity, error) {
@@ -220,32 +206,39 @@ func verifySignature(data, signature, pubKey []byte) (string, error) {
 }
 
 // dearmor returns the binary OpenPGP data in data: data itself when it is
-// not armored, or else the body of its armored block. Armored data must be
+// not armored, or else the bodies of all its armored blocks, one after
-// one block and nothing else: its first line is the only BEGIN line and
+// another. armor.Decode reads only the first block it finds, so dearmor
-// its last line the only END line, white space around them aside.
+// decodes the text after each block's END line in turn, and a second key
-// armor.Decode skips any text before a BEGIN line and reads only the first
+// or signature after the first is read too.
-// block, so without this a second key or signature would go unseen.
 func dearmor(data []byte) ([]byte, error) {
-	if !bytes.Contains(data, []byte(armorBegin)) {
+	var binary []byte
+
+	rest := data
+
+	for {
+		block, err := armor.Decode(bytes.NewReader(rest))
+		if errors.Is(err, io.EOF) {
+			break
+		}
+
+		if err != nil {
+			return nil, err
+		}
+
+		body, err := io.ReadAll(block.Body)
+		if err != nil {
+			return nil, err
+		}
+
+		binary = append(binary, body...)
+		_, rest, _ = bytes.Cut(rest, []byte(armorEnd))
+	}
+
+	if binary == nil {
 		return data, nil
 	}
 
-	text := bytes.TrimSpace(data)
+	return binary, nil
-	lastLine := text[bytes.LastIndexByte(text, '\n')+1:]
-
-	if !bytes.HasPrefix(text, []byte(armorBegin)) ||
-		bytes.Count(text, []byte(armorBegin)) != 1 ||
-		!bytes.HasPrefix(lastLine, []byte(armorEnd)) ||
-		bytes.Count(text, []byte(armorEnd)) != 1 {
-		return nil, errNotOneArmoredBlock
-	}
-
-	block, err := armor.Decode(bytes.NewReader(text))
-	if err != nil {
-		return nil, err
-	}
-
-	return io.ReadAll(block.Body)
 }
 
 // countPackets returns how many packets in the binary OpenPGP data have

mfer/openpgp_test.go

@@ -403,12 +403,12 @@ func TestManifestSignedByGPGLoads(t *testing.T) {
 }
 
 // TestManifestRefusesSecondEmbeddedKey loads manifests whose embedded
-// public key block holds another key besides the key that signed it: as a
+// public key block holds another key besides the key that signed it: in an
-// public key, as a secret key with no user ID, which openpgp.ReadKeyRing
+// armored block of its own, in the same armored block, as a secret key
-// skips, and written as a subkey packet at the start of the block, which
+// with no user ID, which openpgp.ReadKeyRing skips, and written as a
-// openpgp.ReadKeyRing reads as a primary key. Loading must refuse each,
+// subkey packet at the start of the block, which openpgp.ReadKeyRing reads
-// although the signature is good and the signer field names the key that
+// as a primary key. Loading must refuse each, although the signature is
-// made it.
+// good and the signer field names the key that made it.
 func TestManifestRefusesSecondEmbeddedKey(t *testing.T) {
 	t.Parallel()
 
@@ -424,9 +424,12 @@ func TestManifestRefusesSecondEmbeddedKey(t *testing.T) {
 	otherAsSubkey.PrimaryKey.IsSubkey = true
 
 	for name, block := range map[string][]byte{
-		"public key":                 armoredPublicKeys(t, other, signer),
+		"armored block of its own": joinArmored(
-		"secret key without user ID": armoredSecretKeys(t, signer, otherWithoutUserID),
+			armoredPublicKeys(t, other), armoredPublicKeys(t, signer)),
-		"subkey packet first":        armoredPublicKeys(t, otherAsSubkey, signer),
+		"same armored block": armoredPublicKeys(t, other, signer),
+		"secret key without user ID": joinArmored(
+			armoredPublicKeys(t, signer), armoredSecretKeys(t, otherWithoutUserID)),
+		"subkey packet first": armoredPublicKeys(t, otherAsSubkey, signer),
 	} {
 		t.Run(name, func(t *testing.T) {
 			t.Parallel()
@@ -451,12 +454,10 @@ func TestManifestRefusesSecondEmbeddedKeyWithoutUserID(t *testing.T) {
 	other := newTestKey(t, nil)
 	other.Identities = map[string]*openpgp.Identity{}
 
-	signer := newTestKey(t, nil)
+	manifest := rewriteOuter(t, signedTestManifest(t, testSigningOptions(t)),
-
-	manifest := rewriteOuter(t, signedTestManifest(t,
-		&SigningOptions{SecretKey: armoredSecretKeys(t, signer)}),
 		func(outer *MFFileOuter) {
-			outer.SigningPubKey = armoredPublicKeys(t, other, signer)
+			outer.SigningPubKey = joinArmored(
+				armoredPublicKeys(t, other), outer.GetSigningPubKey())
 		})
 
 	_, err := NewManifestFromReader(bytes.NewReader(manifest))
@@ -464,63 +465,20 @@ func TestManifestRefusesSecondEmbeddedKeyWithoutUserID(t *testing.T) {
 }
 
 // TestManifestRefusesTwoSignatures loads a manifest whose signature field
-// holds its good signature twice, not armored. Loading must refuse it.
+// holds its good signature twice. Loading must refuse it.
 func TestManifestRefusesTwoSignatures(t *testing.T) {
 	t.Parallel()
 
 	manifest := rewriteOuter(t, signedTestManifest(t, testSigningOptions(t)),
 		func(outer *MFFileOuter) {
-			sig, err := dearmor(outer.GetSignature())
+			outer.Signature = joinArmored(
-			require.NoError(t, err)
+				outer.GetSignature(), outer.GetSignature())
-
-			outer.Signature = slices.Concat(sig, sig)
 		})
 
 	_, err := NewManifestFromReader(bytes.NewReader(manifest))
 	require.ErrorIs(t, err, errNotOneSignature)
 }
 
-// TestManifestRefusesFieldNotOneArmoredBlock loads manifests whose
-// signature or embedded public key block holds its good armored block with
-// something else: a second armored block, text after the END line, or many
-// END lines before the block. Decoding the block once for each END line
-// before it would take time and memory that grow with the square of the
-// field's size. Loading must refuse each.
-func TestManifestRefusesFieldNotOneArmoredBlock(t *testing.T) {
-	t.Parallel()
-
-	manifest := signedTestManifest(t, testSigningOptions(t))
-
-	for name, change := range map[string]func([]byte) []byte{
-		"second armored block": func(block []byte) []byte {
-			return joinArmored(block, block)
-		},
-		"text after the END line": func(block []byte) []byte {
-			return slices.Concat(block, []byte("\nmore text\n"))
-		},
-		"END lines before the block": func(block []byte) []byte {
-			return slices.Concat(
-				[]byte(strings.Repeat(armorEnd+"\n", 1000)), block)
-		},
-	} {
-		t.Run(name, func(t *testing.T) {
-			t.Parallel()
-
-			for _, changed := range [][]byte{
-				rewriteOuter(t, manifest, func(outer *MFFileOuter) {
-					outer.Signature = change(outer.GetSignature())
-				}),
-				rewriteOuter(t, manifest, func(outer *MFFileOuter) {
-					outer.SigningPubKey = change(outer.GetSigningPubKey())
-				}),
-			} {
-				_, err := NewManifestFromReader(bytes.NewReader(changed))
-				require.ErrorIs(t, err, errNotOneArmoredBlock)
-			}
-		})
-	}
-}
-
 // TestManifestSignedWithSubkey signs with a key that has a signing subkey,
 // which signs in place of the primary key. The manifest must load, with
 // the primary key's fingerprint as signer.