Add (skopeo generate-sigstore-key)

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

README.md

@@ -208,6 +208,7 @@ Please read the [contribution guide](CONTRIBUTING.md) if you want to collaborate
 | -------------------------------------------------- | ---------------------------------------------------------------------------------------------|
 | [skopeo-copy(1)](/docs/skopeo-copy.1.md)           | Copy an image (manifest, filesystem layers, signatures) from one location to another.        |
 | [skopeo-delete(1)](/docs/skopeo-delete.1.md)       | Mark the image-name for later deletion by the registry's garbage collector.                                                                |
+| [skopeo-generate-sigstore-key(1)](/docs/skopeo-generate-sigstore-key.1.md)    | Generate a sigstore public/private key pair.  |
 | [skopeo-inspect(1)](/docs/skopeo-inspect.1.md)     | Return  low-level  information about image-name in a registry.                                |
 | [skopeo-list-tags(1)](/docs/skopeo-list-tags.1.md) | Return a list of tags for the transport-specific image repository.                               |
 | [skopeo-login(1)](/docs/skopeo-login.1.md)         | Login to a container registry.                                                               |

cmd/skopeo/generate_sigstore_key.go

@@ -0,0 +1,90 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
+
+	"github.com/containers/image/v5/pkg/cli"
+	"github.com/containers/image/v5/signature/sigstore"
+	"github.com/spf13/cobra"
+)
+
+type generateSigstoreKeyOptions struct {
+	outputPrefix   string
+	passphraseFile string
+}
+
+func generateSigstoreKeyCmd() *cobra.Command {
+	var opts generateSigstoreKeyOptions
+	cmd := &cobra.Command{
+		Use:     "generate-sigstore-key [command options] --output-prefix PREFIX",
+		Short:   "Generate a sigstore public/private key pair",
+		RunE:    commandAction(opts.run),
+		Example: "skopeo generate-sigstore-key --output-prefix my-key",
+	}
+	adjustUsage(cmd)
+	flags := cmd.Flags()
+	flags.StringVar(&opts.outputPrefix, "output-prefix", "", "Write the keys to `PREFIX`.pub and `PREFIX`.private")
+	flags.StringVar(&opts.passphraseFile, "passphrase-file", "", "Read a passphrase for the private key from `PATH`")
+	return cmd
+}
+
+// ensurePathDoesNotExist verifies that path does not refer to an existing file,
+// and returns an error if so.
+func ensurePathDoesNotExist(path string) error {
+	switch _, err := os.Stat(path); {
+	case err == nil:
+		return fmt.Errorf("Refusing to overwrite existing %q", path)
+	case errors.Is(err, fs.ErrNotExist):
+		return nil
+	default:
+		return fmt.Errorf("Error checking existence of %q: %w", path, err)
+	}
+}
+
+func (opts *generateSigstoreKeyOptions) run(args []string, stdout io.Writer) error {
+	if len(args) != 0 || opts.outputPrefix == "" {
+		return errors.New("Usage: generate-sigstore-key --output-prefix PREFIX")
+	}
+
+	pubKeyPath := opts.outputPrefix + ".pub"
+	privateKeyPath := opts.outputPrefix + ".private"
+	if err := ensurePathDoesNotExist(pubKeyPath); err != nil {
+		return err
+	}
+	if err := ensurePathDoesNotExist(privateKeyPath); err != nil {
+		return err
+	}
+
+	var passphrase string
+	if opts.passphraseFile != "" {
+		p, err := cli.ReadPassphraseFile(opts.passphraseFile)
+		if err != nil {
+			return err
+		}
+		passphrase = p
+	} else {
+		p, err := promptForPassphrase(privateKeyPath, os.Stdin, os.Stdout)
+		if err != nil {
+			return err
+		}
+		passphrase = p
+	}
+
+	keys, err := sigstore.GenerateKeyPair([]byte(passphrase))
+	if err != nil {
+		return fmt.Errorf("Error generating key pair: %w", err)
+	}
+
+	if err := os.WriteFile(privateKeyPath, keys.PrivateKey, 0600); err != nil {
+		return fmt.Errorf("Error writing private key to %q: %w", privateKeyPath, err)
+	}
+	if err := os.WriteFile(pubKeyPath, keys.PublicKey, 0644); err != nil {
+		return fmt.Errorf("Error writing private key to %q: %w", pubKeyPath, err)
+	}
+	fmt.Fprintf(stdout, "Key written to %q and %q", privateKeyPath, pubKeyPath)
+	return nil
+}

cmd/skopeo/generate_sigstore_key_test.go

@@ -0,0 +1,79 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGenerateSigstoreKey(t *testing.T) {
+	// Invalid command-line arguments
+	for _, args := range [][]string{
+		{},
+		{"--output-prefix", "foo", "a1"},
+	} {
+		out, err := runSkopeo(append([]string{"generate-sigstore-key"}, args...)...)
+		assertTestFailed(t, out, err, "Usage")
+	}
+
+	// One of the destination files already exists
+	outputSuffixes := []string{".pub", ".private"}
+	for _, suffix := range outputSuffixes {
+		dir := t.TempDir()
+		prefix := filepath.Join(dir, "prefix")
+		err := os.WriteFile(prefix+suffix, []byte{}, 0600)
+		require.NoError(t, err)
+		out, err := runSkopeo("generate-sigstore-key",
+			"--output-prefix", prefix, "--passphrase-file", "/dev/null",
+		)
+		assertTestFailed(t, out, err, "Refusing to overwrite")
+	}
+
+	// One of the destinations is inaccessible (simulate by a symlink that tries to
+	// traverse a non-directory)
+	for _, suffix := range outputSuffixes {
+		dir := t.TempDir()
+		nonDirectory := filepath.Join(dir, "nondirectory")
+		err := os.WriteFile(nonDirectory, []byte{}, 0600)
+		require.NoError(t, err)
+		prefix := filepath.Join(dir, "prefix")
+		err = os.Symlink(filepath.Join(nonDirectory, "unaccessible"), prefix+suffix)
+		require.NoError(t, err)
+		out, err := runSkopeo("generate-sigstore-key",
+			"--output-prefix", prefix, "--passphrase-file", "/dev/null",
+		)
+		assertTestFailed(t, out, err, prefix+suffix) // + an OS-specific error message
+	}
+	destDir := t.TempDir()
+	// Error reading passphrase
+	out, err := runSkopeo("generate-sigstore-key",
+		"--output-prefix", filepath.Join(destDir, "prefix"),
+		"--passphrase-file", filepath.Join(destDir, "this-does-not-exist"),
+	)
+	assertTestFailed(t, out, err, "this-does-not-exist")
+
+	// (The interactive passphrase prompting is not yet tested)
+
+	// Error writing outputs is untested: when unit tests run as root, we can’t use permissions on a directory to cause write failures,
+	// with the --output-prefix mechanism, and refusing to even start writing to pre-exisiting files, directories are the only mechanism
+	// we have to trigger a write failure.
+
+	// Success
+	// Just a smoke-test, useability of the keys is tested in the generate implementation.
+	dir := t.TempDir()
+	prefix := filepath.Join(dir, "prefix")
+	passphraseFile := filepath.Join(dir, "passphrase")
+	err = os.WriteFile(passphraseFile, []byte("some passphrase"), 0600)
+	require.NoError(t, err)
+	out, err = runSkopeo("generate-sigstore-key",
+		"--output-prefix", prefix, "--passphrase-file", passphraseFile,
+	)
+	assert.NoError(t, err)
+	for _, suffix := range outputSuffixes {
+		assert.Contains(t, out, prefix+suffix)
+	}
+
+}

cmd/skopeo/main.go

@@ -98,6 +98,7 @@ func createApp() (*cobra.Command, *globalOptions) {
 	rootCommand.AddCommand(
 		copyCmd(&opts),
 		deleteCmd(&opts),
+		generateSigstoreKeyCmd(),
 		inspectCmd(&opts),
 		layersCmd(&opts),
 		loginCmd(&opts),

docs/skopeo-generate-sigstore-key.1.md

@@ -0,0 +1,47 @@
+% skopeo-generate-sigstore-key(1)
+
+## NAME
+skopeo\-generate-sigstore-key - Generate a sigstore public/private key pair.
+
+## SYNOPSIS
+**skopeo generate-sigstore-key** [*options*] **--output-prefix** _prefix_
+
+## DESCRIPTION
+
+Generates a public/private key pair suitable for creating sigstore image signatures.
+The private key is encrypted with a passphrase;
+if one is not provided using an option, this command prompts for it interactively.
+
+The private key is written to _prefix_**.private** .
+The private key is written to _prefix_**.pub** .
+
+## OPTIONS
+
+**--help**, **-h**
+
+Print usage statement
+
+**--output-prefix** _prefix_
+
+Mandatory.
+Path prefix for the output keys (_prefix_**.private** and _prefix_**.pub**).
+
+**--passphrase-file** _path_
+
+The passphare to use to encrypt the private key.
+Only the first line will be read.
+A passphrase stored in a file is of questionable security if other users can read this file.
+Do not use this option if at all avoidable.
+
+## EXAMPLES
+
+```sh
+$ skopeo generate-sigstore-key --output-prefix mykey
+```
+
+# SEE ALSO
+skopeo(1), skopeo-copy(1), containers-policy.json(5)
+
+## AUTHORS
+
+Miloslav Trmač <mitr@redhat.com>

docs/skopeo.1.md

@@ -101,6 +101,7 @@ Print the version number
 | ----------------------------------------- | ------------------------------------------------------------------------------ |
 | [skopeo-copy(1)](skopeo-copy.1.md)        | Copy an image (manifest, filesystem layers, signatures) from one location to another. |
 | [skopeo-delete(1)](skopeo-delete.1.md)    | Mark the _image-name_ for later deletion by the registry's garbage collector.  |
+| [skopeo-generate-sigstore-key(1)](skopeo-generate-sigstore-key.1.md)    | Generate a sigstore public/private key pair.  |
 | [skopeo-inspect(1)](skopeo-inspect.1.md)  | Return low-level information about _image-name_ in a registry.                 |
 | [skopeo-list-tags(1)](skopeo-list-tags.1.md)  | List image names in a transport-specific collection of images.|
 | [skopeo-login(1)](skopeo-login.1.md)  | Login to a container registry. |