feat: add gpg integration

This commit adds gpg system integration. This is done through two new
packages: gpgbin, which handles the system calls and parsing; and gpg
which is mostly a copy of emersion/go-pgpmail with modifications to
interface with package gpgbin. gpg includes tests for many cases, and
by it's nature also tests package gpgbin. I separated these in case an
external dependency is ever used for the gpg sys-calls/parsing (IE we
mirror how go-pgpmail+openpgp currently are dependencies)

Two new config options are introduced:
* pgp-provider. If it is not explicitly set to "gpg", aerc will default to
it's internal pgp provider
* pgp-key-id: (Optionally) specify a key by short or long keyId

Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
Acked-by: Koni Marti <koni.marti@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>

config/aerc.conf

@@ -3,6 +3,12 @@
 
 [general]
 #
+# If set to "gpg", aerc will use system gpg binary and keystore for all crypto
+# operations. Otherwise, the internal openpgp implemenation will be used.
+#
+# Default: internal
+pgp-provider=internal
+
 # By default, the file permissions of accounts.conf must be restrictive and
 # only allow reading by the file owner (0600). Set this option to true to
 # ignore this permission check. Use this with care as it may expose your

config/config.go

@@ -104,6 +104,7 @@ type AccountConfig struct {
 	SignatureCmd      string
 	EnableFoldersSort bool     `ini:"enable-folders-sort"`
 	FoldersSort       []string `ini:"folders-sort" delim:","`
+	PgpKeyId          string   `ini:"pgp-key-id"`
 }
 
 type BindingConfig struct {
@@ -248,6 +249,8 @@ func loadAccountConfig(path string) ([]AccountConfig, error) {
 				account.Archive = val
 			} else if key == "enable-folders-sort" {
 				account.EnableFoldersSort, _ = strconv.ParseBool(val)
+			} else if key == "pgp-key-id" {
+				account.PgpKeyId = val
 			} else if key != "name" {
 				account.Params[key] = val
 			}
@@ -582,13 +585,14 @@ func validateBorderChars(section *ini.Section, config *UIConfig) error {
 
 func validatePgpProvider(section *ini.Section) error {
 	m := map[string]bool{
+		"gpg":      true,
 		"internal": true,
 	}
 	for key, val := range section.KeysHash() {
 		switch key {
 		case "pgp-provider":
 			if !m[strings.ToLower(val)] {
-				return fmt.Errorf("%v must be 'internal'", key)
+				return fmt.Errorf("%v must be either 'gpg' or 'internal'", key)
 			}
 		}
 	}

doc/aerc-config.5.scd

@@ -30,6 +30,13 @@ These options are configured in the *[general]* section of aerc.conf.
 *default-save-path*
 	Used as a default path for save operations if no other path is specified.
 
+*pgp-provider*
+	If set to "gpg", aerc will use system gpg binary and keystore for all
+	crypto operations. Otherwise, the internal openpgp implemenation will be
+	used.
+
+	Default: internal
+
 *unsafe-accounts-conf*
 	By default, the file permissions of accounts.conf must be restrictive
 	and only allow reading by the file owner (_0600_). Set this option to
@@ -579,6 +586,10 @@ Note that many of these configuration options are written for you, such as
 
 	Default: none
 
+*pgp-key-id*
+	Specify the key id to use when signing a message. Can be either short or
+	long key id. If unset, aerc will look up the key by email
+
 *postpone*
 	Specifies the folder to save postponed messages to.
 

lib/crypto/crypto.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"log"
 
+	"git.sr.ht/~rjarry/aerc/lib/crypto/gpg"
 	"git.sr.ht/~rjarry/aerc/lib/crypto/pgp"
 	"git.sr.ht/~rjarry/aerc/models"
 	"github.com/ProtonMail/go-crypto/openpgp"
@@ -22,6 +23,8 @@ type Provider interface {
 
 func New(s string) Provider {
 	switch s {
+	case "gpg":
+		return &gpg.Mail{}
 	default:
 		return &pgp.Mail{}
 	}

lib/crypto/gpg/gpg.go

@@ -0,0 +1,62 @@
+package gpg
+
+import (
+	"bytes"
+	"io"
+	"log"
+	"os/exec"
+
+	"git.sr.ht/~rjarry/aerc/lib/crypto/gpg/gpgbin"
+	"git.sr.ht/~rjarry/aerc/models"
+	"github.com/ProtonMail/go-crypto/openpgp"
+	"github.com/emersion/go-message/mail"
+)
+
+// Mail satisfies the PGPProvider interface in aerc
+type Mail struct {
+	logger *log.Logger
+}
+
+func (m *Mail) Init(l *log.Logger) error {
+	m.logger = l
+	_, err := exec.LookPath("gpg")
+	return err
+}
+
+func (m *Mail) Decrypt(r io.Reader, decryptKeys openpgp.PromptFunction) (*models.MessageDetails, error) {
+	gpgReader, err := Read(r)
+	if err != nil {
+		return nil, err
+	}
+	md := gpgReader.MessageDetails
+	md.SignatureValidity = models.Valid
+	if md.SignatureError != "" {
+		md.SignatureValidity = handleSignatureError(md.SignatureError)
+	}
+	return md, nil
+}
+
+func (m *Mail) ImportKeys(r io.Reader) error {
+	return gpgbin.Import(r)
+}
+
+func (m *Mail) Encrypt(buf *bytes.Buffer, rcpts []string, signer string, decryptKeys openpgp.PromptFunction, header *mail.Header) (io.WriteCloser, error) {
+
+	return Encrypt(buf, header.Header.Header, rcpts, signer)
+}
+
+func (m *Mail) Sign(buf *bytes.Buffer, signer string, decryptKeys openpgp.PromptFunction, header *mail.Header) (io.WriteCloser, error) {
+	return Sign(buf, header.Header.Header, signer)
+}
+
+func (m *Mail) Close() {}
+
+func handleSignatureError(e string) models.SignatureValidity {
+	if e == "gpg: missing public key" {
+		return models.UnknownEntity
+	}
+	if e == "gpg: header hash does not match actual sig hash" {
+		return models.MicalgMismatch
+	}
+	return models.UnknownValidity
+}

lib/crypto/gpg/gpg_test.go

@@ -0,0 +1,167 @@
+package gpg
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"log"
+	"os/exec"
+	"strings"
+	"testing"
+
+	"git.sr.ht/~rjarry/aerc/models"
+)
+
+func TestHasGpg(t *testing.T) {
+	gpgmail := new(Mail)
+	hasGpg := gpgmail.Init(new(log.Logger))
+
+	if hasGpg != nil {
+		t.Errorf("System does not have GPG")
+	}
+}
+
+func CleanUp() {
+	cmd := exec.Command("gpg", "--batch", "--yes", "--delete-secret-and-public-keys", testKeyId)
+	err := cmd.Run()
+	if err != nil {
+		fmt.Println("Test cleanup failed: you may need to delete the test keys from your GPG keyring")
+		return
+	}
+}
+
+func toCRLF(s string) string {
+	return strings.ReplaceAll(s, "\n", "\r\n")
+}
+
+func deepEqual(t *testing.T, r *models.MessageDetails, expect *models.MessageDetails) {
+	var resBuf bytes.Buffer
+	if _, err := io.Copy(&resBuf, r.Body); err != nil {
+		t.Fatalf("io.Copy() = %v", err)
+	}
+
+	var expBuf bytes.Buffer
+	if _, err := io.Copy(&expBuf, expect.Body); err != nil {
+		t.Fatalf("io.Copy() = %v", err)
+	}
+
+	if resBuf.String() != expBuf.String() {
+		t.Errorf("MessagesDetails.Body = \n%v\n but want \n%v", resBuf.String(), expBuf.String())
+	}
+
+	if r.IsEncrypted != expect.IsEncrypted {
+		t.Errorf("IsEncrypted = \n%v\n but want \n%v", r.IsEncrypted, expect.IsEncrypted)
+	}
+	if r.IsSigned != expect.IsSigned {
+		t.Errorf("IsSigned = \n%v\n but want \n%v", r.IsSigned, expect.IsSigned)
+	}
+	if r.SignedBy != expect.SignedBy {
+		t.Errorf("SignedBy = \n%v\n but want \n%v", r.SignedBy, expect.SignedBy)
+	}
+	if r.SignedByKeyId != expect.SignedByKeyId {
+		t.Errorf("SignedByKeyId = \n%v\n but want \n%v", r.SignedByKeyId, expect.SignedByKeyId)
+	}
+	if r.SignatureError != expect.SignatureError {
+		t.Errorf("SignatureError = \n%v\n but want \n%v", r.SignatureError, expect.SignatureError)
+	}
+	if r.DecryptedWith != expect.DecryptedWith {
+		t.Errorf("DecryptedWith = \n%v\n but want \n%v", r.DecryptedWith, expect.DecryptedWith)
+	}
+	if r.DecryptedWithKeyId != expect.DecryptedWithKeyId {
+		t.Errorf("DecryptedWithKeyId = \n%v\n but want \n%v", r.DecryptedWithKeyId, expect.DecryptedWithKeyId)
+	}
+}
+
+const testKeyId = `B1A8669354153B799F2217BF307215C13DF7A964`
+
+const testPrivateKeyArmored = `-----BEGIN PGP PRIVATE KEY BLOCK-----
+
+lQOYBF5FJf8BCACvlKhSSsv4P8C3Wbv391SrNUBtFquoMuWKtuCr/Ks6KHuofGLn
+bM55uBSQp908aITBDPkaOPsQ3OvwgF7SM8bNIDVpO7FHzCEg2Ysp99iPET/+LsbY
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++5anTnUn
+=gemU
+-----END PGP PRIVATE KEY BLOCK-----
+`
+
+const testPublicKeyArmored = `-----BEGIN PGP PUBLIC KEY BLOCK-----
+
+mQENBF5FJf8BCACvlKhSSsv4P8C3Wbv391SrNUBtFquoMuWKtuCr/Ks6KHuofGLn
+bM55uBSQp908aITBDPkaOPsQ3OvwgF7SM8bNIDVpO7FHzCEg2Ysp99iPET/+LsbY
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+HAd7N0SyGHT5s6gK1FSx29be1qiPwUu5KR2jpm3RjgpbymnOWe4C6iiYCFQ85IX+
+LzpE+p9bB02PUrmzOb4MBV6E5mg30UjXIX01+bwZq5XSB4/FaUrQOAxLuRvVRjK0
+CEcFbPGIlkPSW6s4M9xCC2sQi7caFKVK6Zqf78KbOwAHqfS0x9u2jtTIhsgCjGTI
+AOQ5lNwpLEMjwLias6e5sM6hcK9Wo+A9Sw23f8lMau5clOZTJeyAUAff+5anTnUn
+=ZjQT
+-----END PGP PUBLIC KEY BLOCK-----
+`

lib/crypto/gpg/gpgbin/decrypt.go

@@ -0,0 +1,34 @@
+package gpgbin
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+
+	"git.sr.ht/~rjarry/aerc/models"
+)
+
+// Decrypt runs gpg --decrypt on the contents of r. If the packet is signed,
+// the signature is also verified
+func Decrypt(r io.Reader) (*models.MessageDetails, error) {
+	md := new(models.MessageDetails)
+	orig, err := ioutil.ReadAll(r)
+	if err != nil {
+		return md, err
+	}
+	args := []string{"--decrypt"}
+	g := newGpg(bytes.NewReader(orig), args)
+	err = g.cmd.Run()
+	if err != nil {
+		err = parseError(g.stderr.String())
+		switch GPGErrors[err.Error()] {
+		case ERROR_NO_PGP_DATA_FOUND:
+			md.Body = bytes.NewReader(orig)
+			return md, nil
+		default:
+		}
+	}
+	outRdr := bytes.NewReader(g.stdout.Bytes())
+	parse(outRdr, md)
+	return md, nil
+}

lib/crypto/gpg/gpgbin/encrypt.go

@@ -0,0 +1,35 @@
+package gpgbin
+
+import (
+	"bytes"
+	"io"
+
+	"git.sr.ht/~rjarry/aerc/models"
+)
+
+// Encrypt runs gpg --encrypt [--sign] -r [recipient]. The default is to have
+// --trust-model always set
+func Encrypt(r io.Reader, to []string, from string) ([]byte, error) {
+	//TODO probably shouldn't have --trust-model always a default
+	args := []string{
+		"--armor",
+		"--trust-model", "always",
+	}
+	if from != "" {
+		args = append(args, "--sign", "--default-key", from)
+	}
+	for _, rcpt := range to {
+		args = append(args, "--recipient", rcpt)
+	}
+	args = append(args, "--encrypt", "-")
+
+	g := newGpg(r, args)
+	g.cmd.Run()
+	outRdr := bytes.NewReader(g.stdout.Bytes())
+	var md models.MessageDetails
+	parse(outRdr, &md)
+	var buf bytes.Buffer
+	io.Copy(&buf, md.Body)
+
+	return buf.Bytes(), nil
+}

lib/crypto/gpg/gpgbin/gpgbin.go

@@ -0,0 +1,262 @@
+package gpgbin
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+
+	"git.sr.ht/~rjarry/aerc/models"
+	"github.com/mattn/go-isatty"
+)
+
+// gpg represents a gpg command with buffers attached to stdout and stderr
+type gpg struct {
+	cmd    *exec.Cmd
+	stdout bytes.Buffer
+	stderr bytes.Buffer
+}
+
+// newGpg creates a new gpg command with buffers attached
+func newGpg(stdin io.Reader, args []string) *gpg {
+	g := new(gpg)
+	g.cmd = exec.Command("gpg", "--status-fd", "1", "--batch")
+	g.cmd.Args = append(g.cmd.Args, args...)
+	g.cmd.Stdin = stdin
+	g.cmd.Stdout = &g.stdout
+	g.cmd.Stderr = &g.stderr
+
+	return g
+}
+
+// parseError parses errors returned by gpg that don't show up with a [GNUPG:]
+// prefix
+func parseError(s string) error {
+	lines := strings.Split(s, "\n")
+	for _, line := range lines {
+		line = strings.ToLower(line)
+		if GPGErrors[line] > 0 {
+			return errors.New(line)
+		}
+	}
+	return errors.New("unknown gpg error")
+}
+
+// fields returns the field name from --status-fd output. See:
+// https://github.com/gpg/gnupg/blob/master/doc/DETAILS
+func field(s string) string {
+	tokens := strings.SplitN(s, " ", 3)
+	if tokens[0] == "[GNUPG:]" {
+		return tokens[1]
+	}
+	return ""
+}
+
+// getIdentity returns the identity of the given key
+func getIdentity(key uint64) string {
+	fpr := fmt.Sprintf("%X", key)
+	cmd := exec.Command("gpg", "--with-colons", "--batch", "--list-keys", fpr)
+
+	var outbuf strings.Builder
+	cmd.Stdout = &outbuf
+	cmd.Run()
+	out := strings.Split(outbuf.String(), "\n")
+	for _, line := range out {
+		if strings.HasPrefix(line, "uid") {
+			flds := strings.Split(line, ":")
+			return flds[9]
+		}
+	}
+	return ""
+}
+
+// longKeyToUint64 returns a uint64 version of the given key
+func longKeyToUint64(key string) (uint64, error) {
+	fpr := string(key[len(key)-16:])
+	fprUint64, err := strconv.ParseUint(fpr, 16, 64)
+	if err != nil {
+		return 0, err
+	}
+	return fprUint64, nil
+}
+
+// parse parses the output of gpg --status-fd
+func parse(r io.Reader, md *models.MessageDetails) error {
+	var (
+		logOut io.Writer
+		logger *log.Logger
+	)
+	if !isatty.IsTerminal(os.Stdout.Fd()) {
+		logOut = os.Stdout
+	} else {
+		logOut = ioutil.Discard
+		os.Stdout, _ = os.Open(os.DevNull)
+	}
+	logger = log.New(logOut, "", log.LstdFlags)
+	var err error
+	var msgContent []byte
+	var msgCollecting bool
+	newLine := []byte("\r\n")
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if field(line) == "PLAINTEXT_LENGTH" {
+			continue
+		}
+		if strings.HasPrefix(line, "[GNUPG:]") {
+			msgCollecting = false
+			logger.Println(line)
+		}
+		if msgCollecting {
+			msgContent = append(msgContent, scanner.Bytes()...)
+			msgContent = append(msgContent, newLine...)
+		}
+
+		switch field(line) {
+		case "ENC_TO":
+			md.IsEncrypted = true
+		case "DECRYPTION_KEY":
+			md.DecryptedWithKeyId, err = parseDecryptionKey(line)
+			md.DecryptedWith = getIdentity(md.DecryptedWithKeyId)
+			if err != nil {
+				return err
+			}
+		case "DECRYPTION_FAILED":
+			return fmt.Errorf("gpg: decryption failed")
+		case "PLAINTEXT":
+			msgCollecting = true
+		case "NEWSIG":
+			md.IsSigned = true
+		case "GOODSIG":
+			t := strings.SplitN(line, " ", 4)
+			md.SignedByKeyId, err = longKeyToUint64(t[2])
+			if err != nil {
+				return err
+			}
+			md.SignedBy = t[3]
+		case "BADSIG":
+			t := strings.SplitN(line, " ", 4)
+			md.SignedByKeyId, err = longKeyToUint64(t[2])
+			if err != nil {
+				return err
+			}
+			md.SignatureError = "gpg: invalid signature"
+			md.SignedBy = t[3]
+		case "EXPSIG":
+			t := strings.SplitN(line, " ", 4)
+			md.SignedByKeyId, err = longKeyToUint64(t[2])
+			if err != nil {
+				return err
+			}
+			md.SignatureError = "gpg: expired signature"
+			md.SignedBy = t[3]
+		case "EXPKEYSIG":
+			t := strings.SplitN(line, " ", 4)
+			md.SignedByKeyId, err = longKeyToUint64(t[2])
+			if err != nil {
+				return err
+			}
+			md.SignatureError = "gpg: signature made with expired key"
+			md.SignedBy = t[3]
+		case "REVKEYSIG":
+			t := strings.SplitN(line, " ", 4)
+			md.SignedByKeyId, err = longKeyToUint64(t[2])
+			if err != nil {
+				return err
+			}
+			md.SignatureError = "gpg: signature made with revoked key"
+			md.SignedBy = t[3]
+		case "ERRSIG":
+			t := strings.SplitN(line, " ", 9)
+			md.SignedByKeyId, err = longKeyToUint64(t[2])
+			if err != nil {
+				return err
+			}
+			if t[7] == "9" {
+				md.SignatureError = "gpg: missing public key"
+			}
+			if t[7] == "4" {
+				md.SignatureError = "gpg: unsupported algorithm"
+			}
+			md.SignedBy = "(unknown signer)"
+		case "BEGIN_ENCRYPTION":
+			msgCollecting = true
+		case "SIG_CREATED":
+			fields := strings.Split(line, " ")
+			micalg, err := strconv.Atoi(fields[4])
+			if err != nil {
+				return fmt.Errorf("gpg: micalg not found")
+			}
+			md.Micalg = micalgs[micalg]
+			msgCollecting = true
+		case "VALIDSIG":
+			fields := strings.Split(line, " ")
+			micalg, err := strconv.Atoi(fields[9])
+			if err != nil {
+				return fmt.Errorf("gpg: micalg not found")
+			}
+			md.Micalg = micalgs[micalg]
+		case "NODATA":
+			md.SignatureError = "gpg: no signature packet found"
+		}
+	}
+	md.Body = bytes.NewReader(msgContent)
+	return nil
+}
+
+// parseDecryptionKey returns primary key from DECRYPTION_KEY line
+func parseDecryptionKey(l string) (uint64, error) {
+	key := strings.Split(l, " ")[3]
+	fpr := string(key[len(key)-16:])
+	fprUint64, err := longKeyToUint64(fpr)
+	if err != nil {
+		return 0, err
+	}
+	getIdentity(fprUint64)
+	return fprUint64, nil
+}
+
+type GPGError int32
+
+const (
+	ERROR_NO_PGP_DATA_FOUND GPGError = iota + 1
+)
+
+var GPGErrors = map[string]GPGError{
+	"gpg: no valid openpgp data found.": ERROR_NO_PGP_DATA_FOUND,
+}
+
+// micalgs represent hash algorithms for signatures. These are ignored by many
+// email clients, but can be used as an additional verification so are sent.
+// Both gpgmail and pgpmail implementations in aerc check for matching micalgs
+var micalgs = map[int]string{
+	1:  "pgp-md5",
+	2:  "pgp-sha1",
+	3:  "pgp-ripemd160",
+	8:  "pgp-sha256",
+	9:  "pgp-sha384",
+	10: "pgp-sha512",
+	11: "pgp-sha224",
+}
+
+func logger(s string) {
+	var (
+		logOut io.Writer
+		logger *log.Logger
+	)
+	if !isatty.IsTerminal(os.Stdout.Fd()) {
+		logOut = os.Stdout
+	} else {
+		logOut = ioutil.Discard
+		os.Stdout, _ = os.Open(os.DevNull)
+	}
+	logger = log.New(logOut, "", log.LstdFlags)
+	logger.Println(s)
+}

lib/crypto/gpg/gpgbin/import.go

@@ -0,0 +1,16 @@
+package gpgbin
+
+import (
+	"io"
+)
+
+// Import runs gpg --import and thus imports both private and public keys
+func Import(r io.Reader) error {
+	args := []string{"--import"}
+	g := newGpg(r, args)
+	err := g.cmd.Run()
+	if err != nil {
+		return err
+	}
+	return nil
+}

lib/crypto/gpg/gpgbin/sign.go

@@ -0,0 +1,27 @@
+package gpgbin
+
+import (
+	"bytes"
+	"io"
+
+	"git.sr.ht/~rjarry/aerc/models"
+)
+
+// Sign creates a detached signature based on the contents of r
+func Sign(r io.Reader, from string) ([]byte, string, error) {
+	args := []string{
+		"--armor",
+		"--detach-sign",
+		"--default-key", from,
+	}
+
+	g := newGpg(r, args)
+	g.cmd.Run()
+
+	outRdr := bytes.NewReader(g.stdout.Bytes())
+	var md models.MessageDetails
+	parse(outRdr, &md)
+	var buf bytes.Buffer
+	io.Copy(&buf, md.Body)
+	return buf.Bytes(), md.Micalg, nil
+}

lib/crypto/gpg/gpgbin/verify.go

@@ -0,0 +1,41 @@
+package gpgbin
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+	"os"
+
+	"git.sr.ht/~rjarry/aerc/models"
+)
+
+// Verify runs gpg --verify. If s is not nil, then gpg interprets the
+// arguments as a detached signature
+func Verify(m io.Reader, s io.Reader) (*models.MessageDetails, error) {
+	args := []string{"--verify"}
+	if s != nil {
+		// Detached sig, save the sig to a tmp file and send msg over stdin
+		sig, err := ioutil.TempFile("", "sig")
+		if err != nil {
+			return nil, err
+		}
+		io.Copy(sig, s)
+		sig.Close()
+		defer os.Remove(sig.Name())
+		args = append(args, sig.Name(), "-")
+	}
+	orig, err := ioutil.ReadAll(m)
+	if err != nil {
+		return nil, err
+	}
+	g := newGpg(bytes.NewReader(orig), args)
+	g.cmd.Run()
+
+	out := bytes.NewReader(g.stdout.Bytes())
+	md := new(models.MessageDetails)
+	parse(out, md)
+
+	md.Body = bytes.NewReader(orig)
+
+	return md, nil
+}

lib/crypto/gpg/reader.go

@@ -0,0 +1,165 @@
+// reader.go largerly mimics github.com/emersion/go-gpgmail, with changes made
+// to interface with the gpg package in aerc
+
+package gpg
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"mime"
+	"strings"
+
+	"git.sr.ht/~rjarry/aerc/lib/crypto/gpg/gpgbin"
+	"git.sr.ht/~rjarry/aerc/models"
+	"github.com/emersion/go-message/textproto"
+)
+
+type Reader struct {
+	Header         textproto.Header
+	MessageDetails *models.MessageDetails
+}
+
+func NewReader(h textproto.Header, body io.Reader) (*Reader, error) {
+	t, params, err := mime.ParseMediaType(h.Get("Content-Type"))
+	if err != nil {
+		return nil, err
+	}
+
+	if strings.EqualFold(t, "multipart/encrypted") && strings.EqualFold(params["protocol"], "application/pgp-encrypted") {
+		mr := textproto.NewMultipartReader(body, params["boundary"])
+		return newEncryptedReader(h, mr)
+	}
+	if strings.EqualFold(t, "multipart/signed") && strings.EqualFold(params["protocol"], "application/pgp-signature") {
+		micalg := params["micalg"]
+		mr := textproto.NewMultipartReader(body, params["boundary"])
+		return newSignedReader(h, mr, micalg)
+	}
+
+	var headerBuf bytes.Buffer
+	textproto.WriteHeader(&headerBuf, h)
+
+	return &Reader{
+		Header: h,
+		MessageDetails: &models.MessageDetails{
+			Body: io.MultiReader(&headerBuf, body),
+		},
+	}, nil
+}
+
+func Read(r io.Reader) (*Reader, error) {
+	br := bufio.NewReader(r)
+
+	h, err := textproto.ReadHeader(br)
+	if err != nil {
+		return nil, err
+	}
+	return NewReader(h, br)
+}
+
+func newEncryptedReader(h textproto.Header, mr *textproto.MultipartReader) (*Reader, error) {
+	p, err := mr.NextPart()
+	if err != nil {
+		return nil, fmt.Errorf("gpgmail: failed to read first part in multipart/encrypted message: %v", err)
+	}
+
+	t, _, err := mime.ParseMediaType(p.Header.Get("Content-Type"))
+	if err != nil {
+		return nil, fmt.Errorf("gpgmail: failed to parse Content-Type of first part in multipart/encrypted message: %v", err)
+	}
+	if !strings.EqualFold(t, "application/pgp-encrypted") {
+		return nil, fmt.Errorf("gpgmail: first part in multipart/encrypted message has type %q, not application/pgp-encrypted", t)
+	}
+
+	metadata, err := textproto.ReadHeader(bufio.NewReader(p))
+	if err != nil {
+		return nil, fmt.Errorf("gpgmail: failed to parse application/pgp-encrypted part: %v", err)
+	}
+	if s := metadata.Get("Version"); s != "1" {
+		return nil, fmt.Errorf("gpgmail: unsupported PGP/MIME version: %q", s)
+	}
+
+	p, err = mr.NextPart()
+	if err != nil {
+		return nil, fmt.Errorf("gpgmail: failed to read second part in multipart/encrypted message: %v", err)
+	}
+	t, _, err = mime.ParseMediaType(p.Header.Get("Content-Type"))
+	if err != nil {
+		return nil, fmt.Errorf("gpgmail: failed to parse Content-Type of second part in multipart/encrypted message: %v", err)
+	}
+	if !strings.EqualFold(t, "application/octet-stream") {
+		return nil, fmt.Errorf("gpgmail: second part in multipart/encrypted message has type %q, not application/octet-stream", t)
+	}
+
+	md, err := gpgbin.Decrypt(p)
+	if err != nil {
+		return nil, fmt.Errorf("gpgmail: failed to read PGP message: %v", err)
+	}
+
+	cleartext := bufio.NewReader(md.Body)
+	cleartextHeader, err := textproto.ReadHeader(cleartext)
+	if err != nil {
+		return nil, fmt.Errorf("gpgmail: failed to read encrypted header: %v", err)
+	}
+
+	t, params, err := mime.ParseMediaType(cleartextHeader.Get("Content-Type"))
+	if err != nil {
+		return nil, err
+	}
+
+	if md.IsEncrypted && !md.IsSigned && strings.EqualFold(t, "multipart/signed") && strings.EqualFold(params["protocol"], "application/pgp-signature") {
+		// RFC 1847 encapsulation, see RFC 3156 section 6.1
+		micalg := params["micalg"]
+		mr := textproto.NewMultipartReader(cleartext, params["boundary"])
+		mds, err := newSignedReader(cleartextHeader, mr, micalg)
+		if err != nil {
+			return nil, fmt.Errorf("gpgmail: failed to read encapsulated multipart/signed message: %v", err)
+		}
+		mds.MessageDetails.IsEncrypted = md.IsEncrypted
+		mds.MessageDetails.DecryptedWith = md.DecryptedWith
+		mds.MessageDetails.DecryptedWithKeyId = md.DecryptedWithKeyId
+		return mds, nil
+	}
+
+	var headerBuf bytes.Buffer
+	textproto.WriteHeader(&headerBuf, cleartextHeader)
+	md.Body = io.MultiReader(&headerBuf, cleartext)
+
+	return &Reader{
+		Header:         h,
+		MessageDetails: md,
+	}, nil
+}
+
+func newSignedReader(h textproto.Header, mr *textproto.MultipartReader, micalg string) (*Reader, error) {
+	micalg = strings.ToLower(micalg)
+	p, err := mr.NextPart()
+	if err != nil {
+		return nil, fmt.Errorf("gpgmail: failed to read signed part in multipart/signed message: %v", err)
+	}
+	var headerBuf bytes.Buffer
+	textproto.WriteHeader(&headerBuf, p.Header)
+	var msg bytes.Buffer
+	headerRdr := bytes.NewReader(headerBuf.Bytes())
+	fullMsg := io.MultiReader(headerRdr, p)
+	io.Copy(&msg, fullMsg)
+
+	sig, err := mr.NextPart()
+	if err != nil {
+		return nil, fmt.Errorf("gpgmail: failed to read pgp part in multipart/signed message: %v", err)
+	}
+
+	md, err := gpgbin.Verify(&msg, sig)
+	if err != nil {
+		return nil, fmt.Errorf("gpgmail: failed to read PGP message: %v", err)
+	}
+	if md.Micalg != micalg && md.SignatureError == "" {
+		md.SignatureError = "gpg: header hash does not match actual sig hash"
+	}
+
+	return &Reader{
+		Header:         h,
+		MessageDetails: md,
+	}, nil
+}

lib/crypto/gpg/reader_test.go

@@ -0,0 +1,308 @@
+package gpg
+
+import (
+	"bytes"
+	"io"
+	"strings"
+	"testing"
+
+	"git.sr.ht/~rjarry/aerc/lib/crypto/gpg/gpgbin"
+	"git.sr.ht/~rjarry/aerc/models"
+)
+
+func importSecretKey() {
+	r := strings.NewReader(testPrivateKeyArmored)
+	gpgbin.Import(r)
+}
+
+func importPublicKey() {
+	r := strings.NewReader(testPublicKeyArmored)
+	gpgbin.Import(r)
+}
+
+func TestReader_encryptedSignedPGPMIME(t *testing.T) {
+	var expect = models.MessageDetails{
+		IsEncrypted:        true,
+		IsSigned:           true,
+		SignedBy:           "John Doe (This is a test key) <john.doe@example.org>",
+		SignedByKeyId:      3490876580878068068,
+		SignatureError:     "",
+		DecryptedWith:      "John Doe (This is a test key) <john.doe@example.org>",
+		DecryptedWithKeyId: 3490876580878068068,
+		Body:               strings.NewReader(testEncryptedBody),
+		Micalg:             "pgp-sha512",
+	}
+
+	importSecretKey()
+	sr := strings.NewReader(testPGPMIMEEncryptedSigned)
+	r, err := Read(sr)
+	if err != nil {
+		t.Fatalf("pgpmail.Read() = %v", err)
+	}
+
+	deepEqual(t, r.MessageDetails, &expect)
+
+	t.Cleanup(CleanUp)
+}
+
+func TestReader_signedPGPMIME(t *testing.T) {
+	var expect = models.MessageDetails{
+		IsEncrypted:        false,
+		IsSigned:           true,
+		SignedBy:           "John Doe (This is a test key) <john.doe@example.org>",
+		SignedByKeyId:      3490876580878068068,
+		SignatureError:     "",
+		DecryptedWith:      "",
+		DecryptedWithKeyId: 0,
+		Body:               strings.NewReader(testSignedBody),
+		Micalg:             "pgp-sha256",
+	}
+
+	importSecretKey()
+	importPublicKey()
+	sr := strings.NewReader(testPGPMIMESigned)
+	r, err := Read(sr)
+	if err != nil {
+		t.Fatalf("pgpmail.Read() = %v", err)
+	}
+
+	deepEqual(t, r.MessageDetails, &expect)
+
+	t.Cleanup(CleanUp)
+}
+
+func TestReader_encryptedSignedEncapsulatedPGPMIME(t *testing.T) {
+	var expect = models.MessageDetails{
+		IsEncrypted:        true,
+		IsSigned:           true,
+		SignedBy:           "John Doe (This is a test key) <john.doe@example.org>",
+		SignedByKeyId:      3490876580878068068,
+		SignatureError:     "",
+		DecryptedWith:      "John Doe (This is a test key) <john.doe@example.org>",
+		DecryptedWithKeyId: 3490876580878068068,
+		Body:               strings.NewReader(testSignedBody),
+		Micalg:             "pgp-sha256",
+	}
+
+	importSecretKey()
+	importPublicKey()
+	sr := strings.NewReader(testPGPMIMEEncryptedSignedEncapsulated)
+	r, err := Read(sr)
+	if err != nil {
+		t.Fatalf("pgpmail.Read() = %v", err)
+	}
+
+	deepEqual(t, r.MessageDetails, &expect)
+
+	var buf bytes.Buffer
+	if _, err := io.Copy(&buf, r.MessageDetails.Body); err != nil {
+		t.Fatalf("io.Copy() = %v", err)
+	}
+}
+func TestReader_signedPGPMIMEInvalid(t *testing.T) {
+	var expect = models.MessageDetails{
+		IsEncrypted:        false,
+		IsSigned:           true,
+		SignedBy:           "John Doe (This is a test key) <john.doe@example.org>",
+		SignedByKeyId:      3490876580878068068,
+		SignatureError:     "gpg: invalid signature",
+		DecryptedWith:      "",
+		DecryptedWithKeyId: 0,
+		Body:               strings.NewReader(testSignedInvalidBody),
+		Micalg:             "",
+	}
+
+	importSecretKey()
+	importPublicKey()
+	sr := strings.NewReader(testPGPMIMESignedInvalid)
+	r, err := Read(sr)
+	if err != nil {
+		t.Fatalf("pgpmail.Read() = %v", err)
+	}
+	deepEqual(t, r.MessageDetails, &expect)
+
+	t.Cleanup(CleanUp)
+}
+
+func TestReader_plaintext(t *testing.T) {
+	sr := strings.NewReader(testPlaintext)
+	r, err := Read(sr)
+	if err != nil {
+		t.Fatalf("pgpmail.Read() = %v", err)
+	}
+
+	var buf bytes.Buffer
+	if _, err := io.Copy(&buf, r.MessageDetails.Body); err != nil {
+		t.Fatalf("io.Copy() = %v", err)
+	}
+
+	if r.MessageDetails.IsEncrypted {
+		t.Errorf("MessageDetails.IsEncrypted != false")
+	}
+	if r.MessageDetails.IsSigned {
+		t.Errorf("MessageDetails.IsSigned != false")
+	}
+
+	if s := buf.String(); s != testPlaintext {
+		t.Errorf("MessagesDetails.UnverifiedBody = \n%v\n but want \n%v", s, testPlaintext)
+	}
+}
+
+var testEncryptedBody = toCRLF(`Content-Type: text/plain
+
+This is an encrypted message!
+`)
+
+var testSignedBody = toCRLF(`Content-Type: text/plain
+
+This is a signed message!
+`)
+
+var testSignedInvalidBody = toCRLF(`Content-Type: text/plain
+
+This is a signed message, but the signature is invalid.
+`)
+
+var testPGPMIMEEncryptedSigned = toCRLF(`From: John Doe <john.doe@example.org>
+To: John Doe <john.doe@example.org>
+Mime-Version: 1.0
+Content-Type: multipart/encrypted; boundary=foo;
+   protocol="application/pgp-encrypted"
+
+--foo
+Content-Type: application/pgp-encrypted
+
+Version: 1
+
+--foo
+Content-Type: application/octet-stream
+
+-----BEGIN PGP MESSAGE-----
+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==
+=P0jf
+-----END PGP MESSAGE-----
+
+--foo--
+`)
+
+var testPGPMIMEEncryptedSignedEncapsulated = toCRLF(`From: John Doe <john.doe@example.org>
+To: John Doe <john.doe@example.org>
+Mime-Version: 1.0
+Content-Type: multipart/encrypted; boundary=foo;
+   protocol="application/pgp-encrypted"
+
+--foo
+Content-Type: application/pgp-encrypted
+
+Version: 1
+
+--foo
+Content-Type: application/octet-stream
+
+-----BEGIN PGP MESSAGE-----
+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+=Ibxd
+-----END PGP MESSAGE-----
+
+--foo--
+`)
+
+var testPGPMIMESigned = toCRLF(`From: John Doe <john.doe@example.org>
+To: John Doe <john.doe@example.org>
+Mime-Version: 1.0
+Content-Type: multipart/signed; boundary=bar; micalg=pgp-sha256;
+   protocol="application/pgp-signature"
+
+--bar
+Content-Type: text/plain
+
+This is a signed message!
+
+--bar
+Content-Type: application/pgp-signature
+
+-----BEGIN PGP SIGNATURE-----
+
+iQEzBAABCAAdFiEEsahmk1QVO3mfIhe/MHIVwT33qWQFAl5FRLgACgkQMHIVwT33
+qWSEQQf/YgRlKlQzSyvm6A52lGIRU3F/z9EGjhCryxj+hSdPlk8O7iZFIjnco4Ea
+7QIlsOj6D4AlLdhyK6c8IZV7rZoTNE5rc6I5UZjM4Qa0XoyLjao28zR252TtwwWJ
+e4+wrTQKcVhCyHO6rkvcCpru4qF5CU+Mi8+sf8CNJJyBgw1Pri35rJWMdoTPTqqz
+kcIGN1JySaI8bbVitJQmnm0FtFTiB7zznv94rMBCiPmPUWd9BSpSBJteJoBLZ+K7
+Y7ws2Dzp2sBo/RLUM18oXd0N9PLXvFGI3IuF8ey1SPzQH3QbBdJSTmLzRlPjK7A1
+HVHFb3vTjd71z9j5IGQQ3Awdw30zMg==
+=gOul
+-----END PGP SIGNATURE-----
+
+--bar--
+`)
+
+var testPGPMIMESignedInvalid = toCRLF(`From: John Doe <john.doe@example.org>
+To: John Doe <john.doe@example.org>
+Mime-Version: 1.0
+Content-Type: multipart/signed; boundary=bar; micalg=pgp-sha256;
+   protocol="application/pgp-signature"
+
+--bar
+Content-Type: text/plain
+
+This is a signed message, but the signature is invalid.
+
+--bar
+Content-Type: application/pgp-signature
+
+-----BEGIN PGP SIGNATURE-----
+
+iQEzBAABCAAdFiEEsahmk1QVO3mfIhe/MHIVwT33qWQFAl5FRLgACgkQMHIVwT33
+qWSEQQf/YgRlKlQzSyvm6A52lGIRU3F/z9EGjhCryxj+hSdPlk8O7iZFIjnco4Ea
+7QIlsOj6D4AlLdhyK6c8IZV7rZoTNE5rc6I5UZjM4Qa0XoyLjao28zR252TtwwWJ
+e4+wrTQKcVhCyHO6rkvcCpru4qF5CU+Mi8+sf8CNJJyBgw1Pri35rJWMdoTPTqqz
+kcIGN1JySaI8bbVitJQmnm0FtFTiB7zznv94rMBCiPmPUWd9BSpSBJteJoBLZ+K7
+Y7ws2Dzp2sBo/RLUM18oXd0N9PLXvFGI3IuF8ey1SPzQH3QbBdJSTmLzRlPjK7A1
+HVHFb3vTjd71z9j5IGQQ3Awdw30zMg==
+=gOul
+-----END PGP SIGNATURE-----
+
+--bar--
+`)
+
+var testPlaintext = toCRLF(`From: John Doe <john.doe@example.org>
+To: John Doe <john.doe@example.org>
+Mime-Version: 1.0
+Content-Type: text/plain
+
+This is a plaintext message!
+`)

lib/crypto/gpg/writer.go

@@ -0,0 +1,179 @@
+// writer.go largerly mimics github.com/emersion/go-pgpmail, with changes made
+// to interface with the gpg package in aerc
+
+package gpg
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"mime"
+
+	"git.sr.ht/~rjarry/aerc/lib/crypto/gpg/gpgbin"
+	"github.com/emersion/go-message/textproto"
+)
+
+type EncrypterSigner struct {
+	msgBuf          bytes.Buffer
+	encryptedWriter io.Writer
+	to              []string
+	from            string
+}
+
+func (es *EncrypterSigner) Write(p []byte) (int, error) {
+	return es.msgBuf.Write(p)
+}
+
+func (es *EncrypterSigner) Close() (err error) {
+	r := bytes.NewReader(es.msgBuf.Bytes())
+	enc, err := gpgbin.Encrypt(r, es.to, es.from)
+	if err != nil {
+		return err
+	}
+	es.encryptedWriter.Write(enc)
+	return nil
+}
+
+type Signer struct {
+	mw        *textproto.MultipartWriter
+	signedMsg bytes.Buffer
+	w         io.Writer
+	from      string
+	header    textproto.Header
+}
+
+func (s *Signer) Write(p []byte) (int, error) {
+	return s.signedMsg.Write(p)
+}
+
+func (s *Signer) Close() (err error) {
+	// TODO should write the whole message up here so we can get the proper micalg from the signature packet
+
+	sig, micalg, err := gpgbin.Sign(bytes.NewReader(s.signedMsg.Bytes()), s.from)
+	if err != nil {
+		return err
+	}
+	params := map[string]string{
+		"boundary": s.mw.Boundary(),
+		"protocol": "application/pgp-signature",
+		"micalg":   micalg,
+	}
+	s.header.Set("Content-Type", mime.FormatMediaType("multipart/signed", params))
+
+	if err = textproto.WriteHeader(s.w, s.header); err != nil {
+		return err
+	}
+	boundary := s.mw.Boundary()
+	fmt.Fprintf(s.w, "--%s\r\n", boundary)
+	s.w.Write(s.signedMsg.Bytes())
+	s.w.Write([]byte("\r\n"))
+
+	var signedHeader textproto.Header
+	signedHeader.Set("Content-Type", "application/pgp-signature")
+	signatureWriter, err := s.mw.CreatePart(signedHeader)
+	if err != nil {
+		return err
+	}
+
+	_, err = signatureWriter.Write(sig)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// for tests
+var forceBoundary = ""
+
+type multiCloser []io.Closer
+
+func (mc multiCloser) Close() error {
+	for _, c := range mc {
+		if err := c.Close(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func Encrypt(w io.Writer, h textproto.Header, rcpts []string, from string) (io.WriteCloser, error) {
+	mw := textproto.NewMultipartWriter(w)
+
+	if forceBoundary != "" {
+		mw.SetBoundary(forceBoundary)
+	}
+
+	params := map[string]string{
+		"boundary": mw.Boundary(),
+		"protocol": "application/pgp-encrypted",
+	}
+	h.Set("Content-Type", mime.FormatMediaType("multipart/encrypted", params))
+
+	if err := textproto.WriteHeader(w, h); err != nil {
+		return nil, err
+	}
+
+	var controlHeader textproto.Header
+	controlHeader.Set("Content-Type", "application/pgp-encrypted")
+	controlWriter, err := mw.CreatePart(controlHeader)
+	if err != nil {
+		return nil, err
+	}
+	if _, err = controlWriter.Write([]byte("Version: 1\r\n")); err != nil {
+		return nil, err
+	}
+
+	var encryptedHeader textproto.Header
+	encryptedHeader.Set("Content-Type", "application/octet-stream")
+	encryptedWriter, err := mw.CreatePart(encryptedHeader)
+	if err != nil {
+		return nil, err
+	}
+
+	var buf bytes.Buffer
+	plaintext := &EncrypterSigner{
+		msgBuf:          buf,
+		encryptedWriter: encryptedWriter,
+		to:              rcpts,
+		from:            from,
+	}
+
+	return struct {
+		io.Writer
+		io.Closer
+	}{
+		plaintext,
+		multiCloser{
+			plaintext,
+			mw,
+		},
+	}, nil
+}
+
+func Sign(w io.Writer, h textproto.Header, from string) (io.WriteCloser, error) {
+	mw := textproto.NewMultipartWriter(w)
+
+	if forceBoundary != "" {
+		mw.SetBoundary(forceBoundary)
+	}
+
+	var msg bytes.Buffer
+	plaintext := &Signer{
+		mw:        mw,
+		signedMsg: msg,
+		w:         w,
+		from:      from,
+		header:    h,
+	}
+
+	return struct {
+		io.Writer
+		io.Closer
+	}{
+		plaintext,
+		multiCloser{
+			plaintext,
+			mw,
+		},
+	}, nil
+}

lib/crypto/gpg/writer_test.go

@@ -0,0 +1,122 @@
+package gpg
+
+import (
+	"bytes"
+	"io"
+	"strings"
+	"testing"
+
+	"git.sr.ht/~rjarry/aerc/lib/crypto/gpg/gpgbin"
+	"git.sr.ht/~rjarry/aerc/models"
+	"github.com/emersion/go-message/textproto"
+)
+
+func init() {
+	forceBoundary = "foo"
+}
+
+func TestEncrypt(t *testing.T) {
+	importPublicKey()
+	importSecretKey()
+	var h textproto.Header
+	h.Set("From", "John Doe <john.doe@example.org>")
+	h.Set("To", "John Doe <john.doe@example.org>")
+
+	var encryptedHeader textproto.Header
+	encryptedHeader.Set("Content-Type", "text/plain")
+
+	var encryptedBody = "This is an encrypted message!\r\n"
+
+	to := []string{"john.doe@example.org"}
+	from := "john.doe@example.org"
+
+	var buf bytes.Buffer
+	cleartext, err := Encrypt(&buf, h, to, from)
+	if err != nil {
+		t.Fatalf("Encrypt() = %v", err)
+	}
+
+	if err = textproto.WriteHeader(cleartext, encryptedHeader); err != nil {
+		t.Fatalf("textproto.WriteHeader() = %v", err)
+	}
+	if _, err = io.WriteString(cleartext, encryptedBody); err != nil {
+		t.Fatalf("io.WriteString() = %v", err)
+	}
+	if err = cleartext.Close(); err != nil {
+		t.Fatalf("ciphertext.Close() = %v", err)
+	}
+
+	md, err := gpgbin.Decrypt(&buf)
+	if err != nil {
+		t.Errorf("Encrypt error: could not decrypt test encryption")
+	}
+	var body bytes.Buffer
+	io.Copy(&body, md.Body)
+	if s := body.String(); s != wantEncrypted {
+		t.Errorf("Encrypt() = \n%v\n but want \n%v", s, wantEncrypted)
+	}
+
+	t.Cleanup(CleanUp)
+}
+
+func TestSign(t *testing.T) {
+	importPublicKey()
+	importSecretKey()
+	var h textproto.Header
+	h.Set("From", "John Doe <john.doe@example.org>")
+	h.Set("To", "John Doe <john.doe@example.org>")
+
+	var signedHeader textproto.Header
+	signedHeader.Set("Content-Type", "text/plain")
+
+	var signedBody = "This is a signed message!\r\n"
+
+	var buf bytes.Buffer
+	cleartext, err := Sign(&buf, h, "john.doe@example.org")
+	if err != nil {
+		t.Fatalf("Encrypt() = %v", err)
+	}
+
+	if err = textproto.WriteHeader(cleartext, signedHeader); err != nil {
+		t.Fatalf("textproto.WriteHeader() = %v", err)
+	}
+	if _, err = io.WriteString(cleartext, signedBody); err != nil {
+		t.Fatalf("io.WriteString() = %v", err)
+	}
+
+	if err = cleartext.Close(); err != nil {
+		t.Fatalf("ciphertext.Close() = %v", err)
+	}
+
+	parts := strings.Split(buf.String(), "\r\n--foo\r\n")
+	msg := strings.NewReader(parts[1])
+	sig := strings.NewReader(parts[2])
+	md, err := gpgbin.Verify(msg, sig)
+	if err != nil {
+		t.Fatalf("gpg.Verify() = %v", err)
+	}
+
+	deepEqual(t, md, &wantSigned)
+}
+
+var wantEncrypted = toCRLF(`Content-Type: text/plain
+
+This is an encrypted message!
+`)
+
+var wantSignedBody = toCRLF(`Content-Type: text/plain
+
+This is a signed message!
+`)
+
+var wantSigned = models.MessageDetails{
+	IsEncrypted:        false,
+	IsSigned:           true,
+	SignedBy:           "John Doe (This is a test key) <john.doe@example.org>",
+	SignedByKeyId:      3490876580878068068,
+	SignatureError:     "",
+	DecryptedWith:      "",
+	DecryptedWithKeyId: 0,
+	Body:               strings.NewReader(wantSignedBody),
+	Micalg:             "pgp-sha256",
+}

lib/crypto/pgp/pgp.go

@@ -79,6 +79,20 @@ func (m *Mail) getEntityByEmail(email string) (e *openpgp.Entity, err error) {
 	return nil, fmt.Errorf("entity not found in keyring")
 }
 
+func (m *Mail) getSignerEntityByKeyId(id string) (*openpgp.Entity, error) {
+	id = strings.ToUpper(id)
+	for _, key := range Keyring.DecryptionKeys() {
+		if key.Entity == nil {
+			continue
+		}
+		kId := key.Entity.PrimaryKey.KeyIdString()
+		if strings.Contains(kId, id) {
+			return key.Entity, nil
+		}
+	}
+	return nil, fmt.Errorf("entity not found in keyring")
+}
+
 func (m *Mail) getSignerEntityByEmail(email string) (e *openpgp.Entity, err error) {
 	for _, key := range Keyring.DecryptionKeys() {
 		if key.Entity == nil {
@@ -157,12 +171,12 @@ func (m *Mail) ImportKeys(r io.Reader) error {
 	return nil
 }
 
-func (m *Mail) Encrypt(buf *bytes.Buffer, rcpts []string, signerEmail string, decryptKeys openpgp.PromptFunction, header *mail.Header) (io.WriteCloser, error) {
+func (m *Mail) Encrypt(buf *bytes.Buffer, rcpts []string, signer string, decryptKeys openpgp.PromptFunction, header *mail.Header) (io.WriteCloser, error) {
 	var err error
 	var to []*openpgp.Entity
-	var signer *openpgp.Entity
+	var signerEntity *openpgp.Entity
-	if signerEmail != "" {
+	if signer != "" {
-		signer, err = m.getSigner(signerEmail, decryptKeys)
+		signerEntity, err = m.getSigner(signer, decryptKeys)
 		if err != nil {
 			return nil, err
 		}
@@ -177,45 +191,50 @@ func (m *Mail) Encrypt(buf *bytes.Buffer, rcpts []string, signerEmail string, de
 	}
 
 	cleartext, err := pgpmail.Encrypt(buf, header.Header.Header,
-		to, signer, nil)
+		to, signerEntity, nil)
 	if err != nil {
 		return nil, err
 	}
 	return cleartext, nil
 }
 
-func (m *Mail) Sign(buf *bytes.Buffer, signerEmail string, decryptKeys openpgp.PromptFunction, header *mail.Header) (io.WriteCloser, error) {
+func (m *Mail) Sign(buf *bytes.Buffer, signer string, decryptKeys openpgp.PromptFunction, header *mail.Header) (io.WriteCloser, error) {
 	var err error
-	var signer *openpgp.Entity
+	var signerEntity *openpgp.Entity
-	if signerEmail != "" {
+	if signer != "" {
-		signer, err = m.getSigner(signerEmail, decryptKeys)
+		signerEntity, err = m.getSigner(signer, decryptKeys)
 		if err != nil {
 			return nil, err
 		}
 	}
-	cleartext, err := pgpmail.Sign(buf, header.Header.Header, signer, nil)
+	cleartext, err := pgpmail.Sign(buf, header.Header.Header, signerEntity, nil)
 	if err != nil {
 		return nil, err
 	}
 	return cleartext, nil
 }
 
-func (m *Mail) getSigner(signerEmail string, decryptKeys openpgp.PromptFunction) (signer *openpgp.Entity, err error) {
+func (m *Mail) getSigner(signer string, decryptKeys openpgp.PromptFunction) (signerEntity *openpgp.Entity, err error) {
+	switch strings.Contains(signer, "@") {
+	case true:
+		signerEntity, err = m.getSignerEntityByEmail(signer)
 		if err != nil {
 			return nil, err
 		}
-	signer, err = m.getSignerEntityByEmail(signerEmail)
+	case false:
+		signerEntity, err = m.getSignerEntityByKeyId(signer)
 		if err != nil {
 			return nil, err
 		}
+	}
 
-	key, ok := signer.SigningKey(time.Now())
+	key, ok := signerEntity.SigningKey(time.Now())
 	if !ok {
-		return nil, fmt.Errorf("no signing key found for %s", signerEmail)
+		return nil, fmt.Errorf("no signing key found for %s", signer)
 	}
 
 	if !key.PrivateKey.Encrypted {
-		return signer, nil
+		return signerEntity, nil
 	}
 
 	_, err = decryptKeys([]openpgp.Key{key}, false)
@@ -223,7 +242,7 @@ func (m *Mail) getSigner(signerEmail string, decryptKeys openpgp.PromptFunction)
 		return nil, err
 	}
 
-	return signer, nil
+	return signerEntity, nil
 }
 
 func handleSignatureError(e string) models.SignatureValidity {

widgets/compose.go

@@ -452,14 +452,16 @@ func (c *Composer) WriteMessage(header *mail.Header, writer io.Writer) error {
 		var cleartext io.WriteCloser
 		var err error
 
-		var signerEmail string
+		signer := ""
 		if c.sign {
-			signerEmail, err = getSenderEmail(c)
+			if c.acctConfig.PgpKeyId != "" {
+				signer = c.acctConfig.PgpKeyId
+			} else {
+				signer, err = getSenderEmail(c)
 				if err != nil {
 					return err
 				}
-		} else {
+			}
-			signerEmail = ""
 		}
 
 		if c.encrypt {
@@ -467,12 +469,12 @@ func (c *Composer) WriteMessage(header *mail.Header, writer io.Writer) error {
 			if err != nil {
 				return err
 			}
-			cleartext, err = c.aerc.Crypto.Encrypt(&buf, rcpts, signerEmail, c.aerc.DecryptKeys, header)
+			cleartext, err = c.aerc.Crypto.Encrypt(&buf, rcpts, signer, c.aerc.DecryptKeys, header)
 			if err != nil {
 				return err
 			}
 		} else {
-			cleartext, err = c.aerc.Crypto.Sign(&buf, signerEmail, c.aerc.DecryptKeys, header)
+			cleartext, err = c.aerc.Crypto.Sign(&buf, signer, c.aerc.DecryptKeys, header)
 			if err != nil {
 				return err
 			}