cmd/age: add -e and support encrypting with -i

This will come in handy for symmetric plugins, but make it require an
explicit -e so that missing a -d can't cause a mistaken encryption.

agessh/agessh.go

@@ -102,6 +102,13 @@ func NewRSAIdentity(key *rsa.PrivateKey) (*RSAIdentity, error) {
 	return i, nil
 }
 
+func (i *RSAIdentity) Recipient() age.Recipient {
+	return &RSARecipient{
+		sshKey: i.sshKey,
+		pubKey: &i.k.PublicKey,
+	}
+}
+
 func (i *RSAIdentity) Unwrap(stanzas []*age.Stanza) ([]byte, error) {
 	return multiUnwrap(i.unwrap, stanzas)
 }
@@ -303,6 +310,13 @@ func ed25519PrivateKeyToCurve25519(pk ed25519.PrivateKey) []byte {
 	return out[:curve25519.ScalarSize]
 }
 
+func (i *Ed25519Identity) Recipient() age.Recipient {
+	return &Ed25519Recipient{
+		sshKey:         i.sshKey,
+		theirPublicKey: i.ourPublicKey,
+	}
+}
+
 func (i *Ed25519Identity) Unwrap(stanzas []*age.Stanza) ([]byte, error) {
 	return multiUnwrap(i.unwrap, stanzas)
 }

agessh/agessh_test.go

@@ -11,6 +11,7 @@ import (
 	"crypto/ed25519"
 	"crypto/rand"
 	"crypto/rsa"
+	"reflect"
 	"testing"
 
 	"filippo.io/age/agessh"
@@ -36,6 +37,11 @@ func TestSSHRSARoundTrip(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	// TODO: replace this with (and go-diff) with go-cmp.
+	if !reflect.DeepEqual(r, i.Recipient()) {
+		t.Fatalf("i.Recipient is different from r")
+	}
+
 	fileKey := make([]byte, 16)
 	if _, err := rand.Read(fileKey); err != nil {
 		t.Fatal(err)
@@ -74,6 +80,11 @@ func TestSSHEd25519RoundTrip(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	// TODO: replace this with (and go-diff) with go-cmp.
+	if !reflect.DeepEqual(r, i.Recipient()) {
+		t.Fatalf("i.Recipient is different from r")
+	}
+
 	fileKey := make([]byte, 16)
 	if _, err := rand.Read(fileKey); err != nil {
 		t.Fatal(err)

agessh/encrypted_keys.go

@@ -55,6 +55,10 @@ func NewEncryptedSSHIdentity(pubKey ssh.PublicKey, pemBytes []byte, passphrase f
 
 var _ age.Identity = &EncryptedSSHIdentity{}
 
+func (i *EncryptedSSHIdentity) Recipient() (age.Recipient, error) {
+	return ParseRecipient(string(ssh.MarshalAuthorizedKey(i.pubKey)))
+}
+
 // Unwrap implements age.Identity. If the private key is still encrypted, and
 // any of the stanzas match the public key, it will request the passphrase. The
 // decrypted private key will be cached after the first successful invocation.

cmd/age/age.go

@@ -18,6 +18,7 @@ import (
 	"strings"
 
 	"filippo.io/age"
+	"filippo.io/age/agessh"
 	"filippo.io/age/armor"
 	"golang.org/x/crypto/ssh/terminal"
 )
@@ -32,20 +33,22 @@ func (f *multiFlag) Set(value string) error {
 }
 
 const usage = `Usage:
-    age (-r RECIPIENT | -R PATH)... [--armor] [-o OUTPUT] [INPUT]
-    age --passphrase [--armor] [-o OUTPUT] [INPUT]
+    age [--encrypt] (-r RECIPIENT | -R PATH)... [--armor] [-o OUTPUT] [INPUT]
+    age [--encrypt] --passphrase [--armor] [-o OUTPUT] [INPUT]
     age --decrypt [-i PATH]... [-o OUTPUT] [INPUT]
 
 Options:
+    -e, --encrypt               Encrypt the input to the output. Default if omitted.
+    -d, --decrypt               Decrypt the input to the output.
     -o, --output OUTPUT         Write the result to the file at path OUTPUT.
     -a, --armor                 Encrypt to a PEM encoded format.
     -p, --passphrase            Encrypt with a passphrase.
     -r, --recipient RECIPIENT   Encrypt to the specified RECIPIENT. Can be repeated.
     -R, --recipients-file PATH  Encrypt to recipients listed at PATH. Can be repeated.
-    -d, --decrypt               Decrypt the input to the output.
     -i, --identity PATH         Use the identity file at PATH. Can be repeated.
 
 INPUT defaults to standard input, and OUTPUT defaults to standard output.
+If OUTPUT exists, it will be overwritten.
 
 RECIPIENT can be an age public key generated by age-keygen ("age1...")
 or an SSH public key ("ssh-ed25519 AAAA...", "ssh-rsa AAAA...").
@@ -59,6 +62,9 @@ one per line, or an SSH key. Empty lines and lines starting with "#" are
 ignored as comments. Multiple key files can be provided, and any unused ones
 will be ignored. "-" may be used to read identities from standard input.
 
+When --encrypt is specified explicitly, -i can also be used to encrypt to an
+identity file symmetrically, instead or in addition to normal recipients.
+
 Example:
     $ age-keygen -o key.txt
     Public key: age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p
@@ -80,16 +86,18 @@ func main() {
 	}
 
 	var (
-		outFlag                       string
-		decryptFlag, armorFlag        bool
-		passFlag, versionFlag         bool
-		recipientFlags, identityFlags multiFlag
-		recipientsFileFlags           multiFlag
+		outFlag                          string
+		decryptFlag, encryptFlag         bool
+		passFlag, versionFlag, armorFlag bool
+		recipientFlags, identityFlags    multiFlag
+		recipientsFileFlags              multiFlag
 	)
 
 	flag.BoolVar(&versionFlag, "version", false, "print the version")
 	flag.BoolVar(&decryptFlag, "d", false, "decrypt the input")
 	flag.BoolVar(&decryptFlag, "decrypt", false, "decrypt the input")
+	flag.BoolVar(&encryptFlag, "e", false, "encrypt the input")
+	flag.BoolVar(&encryptFlag, "encrypt", false, "encrypt the input")
 	flag.BoolVar(&passFlag, "p", false, "use a passphrase")
 	flag.BoolVar(&passFlag, "passphrase", false, "use a passphrase")
 	flag.StringVar(&outFlag, "o", "", "output to `FILE` (default stdout)")
@@ -123,6 +131,9 @@ func main() {
 	}
 	switch {
 	case decryptFlag:
+		if encryptFlag {
+			logFatalf("Error: -e/--encrypt can't be used with -d/--decrypt.")
+		}
 		if armorFlag {
 			logFatalf("Error: -a/--armor can't be used with -d/--decrypt.\n" +
 				"Note that armored files are detected automatically.")
@@ -140,11 +151,11 @@ func main() {
 				"Did you mean to use -i/--identity to specify a private key?")
 		}
 	default: // encrypt
-		if len(identityFlags) > 0 {
-			logFatalf("Error: -i/--identity can't be used in encryption mode.\n" +
+		if len(identityFlags) > 0 && !encryptFlag {
+			logFatalf("Error: -i/--identity can't be used in encryption mode unless symmetric encryption is explicitly selected with -e/--encrypt.\n" +
 				"Did you forget to specify -d/--decrypt?")
 		}
-		if len(recipientFlags) == 0 && len(recipientsFileFlags) == 0 && !passFlag {
+		if len(recipientFlags)+len(recipientsFileFlags)+len(identityFlags) == 0 && !passFlag {
 			logFatalf("Error: missing recipients.\n" +
 				"Did you forget to specify -r/--recipient, -R/--recipients-file or -p/--passphrase?")
 		}
@@ -154,6 +165,9 @@ func main() {
 		if len(recipientsFileFlags) > 0 && passFlag {
 			logFatalf("Error: -p/--passphrase can't be combined with -R/--recipients-file.")
 		}
+		if len(identityFlags) > 0 && passFlag {
+			logFatalf("Error: -p/--passphrase can't be combined with -i/--identity.")
+		}
 	}
 
 	var in io.Reader = os.Stdin
@@ -202,7 +216,7 @@ func main() {
 		}
 		encryptPass(pass, in, out, armorFlag)
 	default:
-		encryptKeys(recipientFlags, recipientsFileFlags, in, out, armorFlag)
+		encryptKeys(recipientFlags, recipientsFileFlags, identityFlags, in, out, armorFlag)
 	}
 }
 
@@ -233,7 +247,7 @@ func passphrasePromptForEncryption() (string, error) {
 	return p, nil
 }
 
-func encryptKeys(keys, files []string, in io.Reader, out io.Writer, armor bool) {
+func encryptKeys(keys, files, identities []string, in io.Reader, out io.Writer, armor bool) {
 	var recipients []age.Recipient
 	for _, arg := range keys {
 		r, err := parseRecipient(arg)
@@ -249,6 +263,19 @@ func encryptKeys(keys, files []string, in io.Reader, out io.Writer, armor bool)
 		}
 		recipients = append(recipients, recs...)
 	}
+	for _, name := range identities {
+		ids, err := parseIdentitiesFile(name)
+		if err != nil {
+			logFatalf("Error reading %q: %v", name, err)
+		}
+		for _, id := range ids {
+			r, err := identityToRecipient(id)
+			if err != nil {
+				logFatalf("Internal error processing %q: %v", name, err)
+			}
+			recipients = append(recipients, r)
+		}
+	}
 	encrypt(recipients, in, out, armor)
 }
 
@@ -322,6 +349,20 @@ func passphrasePrompt() (string, error) {
 	return string(pass), nil
 }
 
+func identityToRecipient(id age.Identity) (age.Recipient, error) {
+	switch id := id.(type) {
+	case *age.X25519Identity:
+		return id.Recipient(), nil
+	case *agessh.RSAIdentity:
+		return id.Recipient(), nil
+	case *agessh.Ed25519Identity:
+		return id.Recipient(), nil
+	case *agessh.EncryptedSSHIdentity:
+		return id.Recipient()
+	}
+	return nil, fmt.Errorf("unexpected identity type: %T", id)
+}
+
 type lazyOpener struct {
 	name string
 	f    *os.File

cmd/age/parse.go

@@ -109,6 +109,9 @@ func sshKeyType(s string) (string, bool) {
 	return "", false
 }
 
+// parseIdentitiesFile parses a file that contains age or SSH keys. It returns
+// one of *age.X25519Identity, *agessh.RSAIdentity, *agessh.Ed25519Identity, or
+// *agessh.EncryptedSSHIdentity.
 func parseIdentitiesFile(name string) ([]age.Identity, error) {
 	var f *os.File
 	if name == "-" {