From 1766e127acba2cde257f721b2270ad0572f38a78 Mon Sep 17 00:00:00 2001
From: Scott Leggett <scott@sl.id.au>
Date: Wed, 28 Jul 2021 21:31:39 +0800
Subject: [PATCH] feat: cache decryption passphrases for keyfiles

---
 internal/assuan/assuan_test.go |  7 ++++-
 internal/server/gpg.go         | 54 +++++++++++++++++++++++-----------
 2 files changed, 43 insertions(+), 18 deletions(-)

diff --git a/internal/assuan/assuan_test.go b/internal/assuan/assuan_test.go
index a5fd9fd..9683a2c 100644
--- a/internal/assuan/assuan_test.go
+++ b/internal/assuan/assuan_test.go
@@ -17,6 +17,7 @@ import (
 	"github.com/smlx/piv-agent/internal/pivservice"
 	"github.com/smlx/piv-agent/internal/securitykey"
 	"github.com/smlx/piv-agent/internal/server"
+	"go.uber.org/zap"
 	"golang.org/x/crypto/cryptobyte"
 	"golang.org/x/crypto/cryptobyte/asn1"
 	"golang.org/x/crypto/openpgp"
@@ -282,7 +283,11 @@ func TestKeyfileSigner(t *testing.T) {
 			if tc.protected {
 				mockPES.EXPECT().GetPGPPassphrase(gomock.Any()).Return([]byte("trustno1"), nil)
 			}
-			g := server.NewGPG(nil, mockPES, nil, tc.path)
+			log, err := zap.NewDevelopment()
+			if err != nil {
+				tt.Fatal(err)
+			}
+			g := server.NewGPG(nil, mockPES, log, tc.path)
 			if _, err := assuan.KeyfileSigner(g, tc.keygrip); err != nil {
 				tt.Fatalf("couldn't find keygrip: %v", err)
 			}
diff --git a/internal/server/gpg.go b/internal/server/gpg.go
index 90d36d1..19c34ff 100644
--- a/internal/server/gpg.go
+++ b/internal/server/gpg.go
@@ -31,6 +31,8 @@ type GPG struct {
 	log              *zap.Logger
 	fallbackPrivKeys []*packet.PrivateKey
 	pinentry         PINEntryService
+	// cache passphrases used for decryption
+	passphrases [][]byte
 }
 
 // LoadFallbackKeys reads the given path and returns any private keys found.
@@ -76,33 +78,51 @@ func NewGPG(p *pivservice.PIVService, pe PINEntryService, l *zap.Logger, path st
 // GetKey returns a matching private RSA key if the keygrip matches, and nil
 // otherwise.
 func (g *GPG) GetKey(keygrip []byte) *rsa.PrivateKey {
+	var pass []byte
+	var err error
 	for _, k := range g.fallbackPrivKeys {
 		pubKey, ok := k.PublicKey.PublicKey.(*rsa.PublicKey)
 		if !ok {
 			continue
 		}
-		if bytes.Equal(keygrip, gpg.KeygripRSA(pubKey)) {
-			if k.Encrypted {
-				pass, err := g.pinentry.GetPGPPassphrase(
-					fmt.Sprintf("%X %X %X %X", k.Fingerprint[:5], k.Fingerprint[5:10],
-						k.Fingerprint[10:15], k.Fingerprint[15:]))
-				if err != nil {
-					g.log.Warn("couldn't get passphrase for key",
-						zap.String("fingerprint", k.KeyIdString()), zap.Error(err))
-					return nil
-				}
-				if err = k.Decrypt(pass); err != nil {
-					g.log.Warn("couldn't decrypt key",
-						zap.String("fingerprint", k.KeyIdString()), zap.Error(err))
+		if !bytes.Equal(keygrip, gpg.KeygripRSA(pubKey)) {
+			continue
+		}
+		if k.Encrypted {
+			// try existing passphrases
+			for _, pass := range g.passphrases {
+				if err = k.Decrypt(pass); err == nil {
+					g.log.Debug("decrypted using cached passphrase",
+						zap.String("fingerprint", k.KeyIdString()))
+					break
 				}
 			}
-			privKey, ok := k.PrivateKey.(*rsa.PrivateKey)
-			if !ok {
-				g.log.Info("not an RSA key", zap.String("fingerprint", k.KeyIdString()))
+		}
+		if k.Encrypted {
+			// ask for a passphrase
+			pass, err = g.pinentry.GetPGPPassphrase(
+				fmt.Sprintf("%X %X %X %X", k.Fingerprint[:5], k.Fingerprint[5:10],
+					k.Fingerprint[10:15], k.Fingerprint[15:]))
+			if err != nil {
+				g.log.Warn("couldn't get passphrase for key",
+					zap.String("fingerprint", k.KeyIdString()), zap.Error(err))
 				return nil
 			}
-			return privKey
+			g.passphrases = append(g.passphrases, pass)
+			if err = k.Decrypt(pass); err != nil {
+				g.log.Warn("couldn't decrypt key",
+					zap.String("fingerprint", k.KeyIdString()), zap.Error(err))
+				return nil
+			}
+			g.log.Debug("decrypted using passphrase",
+				zap.String("fingerprint", k.KeyIdString()))
+		}
+		privKey, ok := k.PrivateKey.(*rsa.PrivateKey)
+		if !ok {
+			g.log.Info("not an RSA key", zap.String("fingerprint", k.KeyIdString()))
+			return nil
 		}
+		return privKey
 	}
 	return nil
 }