backport of commit daf72aa (hashicorp#20901)

Removed byok test; this is unfortunate as it was the strongest
exerciser of this, but sadly it doesn't exist in 1.13 and previous
versions.

Signed-off-by: Alexander Scheel <alex.scheel@hashicorp.com>
Co-authored-by: Alexander Scheel <alex.scheel@hashicorp.com>

builtin/logical/transit/path_backup_test.go

@@ -36,6 +36,7 @@ func TestTransit_BackupRestore(t *testing.T) {
 	testBackupRestore(t, "rsa-2048", "hmac-verify")
 	testBackupRestore(t, "rsa-3072", "hmac-verify")
 	testBackupRestore(t, "rsa-4096", "hmac-verify")
+	testBackupRestore(t, "hmac", "hmac-verify")
 }
 
 func testBackupRestore(t *testing.T, keyType, feature string) {
@@ -54,6 +55,9 @@ func testBackupRestore(t *testing.T, keyType, feature string) {
 			"exportable": true,
 		},
 	}
+	if keyType == "hmac" {
+		keyReq.Data["key_size"] = 32
+	}
 	resp, err = b.HandleRequest(context.Background(), keyReq)
 	if err != nil || (resp != nil && resp.IsError()) {
 		t.Fatalf("resp: %#v\nerr: %v", resp, err)

builtin/logical/transit/path_export.go

@@ -151,7 +151,11 @@ func getExportKey(policy *keysutil.Policy, key *keysutil.KeyEntry, exportType st
 
 	switch exportType {
 	case exportTypeHMACKey:
-		return strings.TrimSpace(base64.StdEncoding.EncodeToString(key.HMACKey)), nil
+		src := key.HMACKey
+		if policy.Type == keysutil.KeyType_HMAC {
+			src = key.Key
+		}
+		return strings.TrimSpace(base64.StdEncoding.EncodeToString(src)), nil
 
 	case exportTypeEncryptionKey:
 		switch policy.Type {

builtin/logical/transit/path_export_test.go

@@ -25,6 +25,7 @@ func TestTransit_Export_KeyVersion_ExportsCorrectVersion(t *testing.T) {
 	verifyExportsCorrectVersion(t, "hmac-key", "ecdsa-p384")
 	verifyExportsCorrectVersion(t, "hmac-key", "ecdsa-p521")
 	verifyExportsCorrectVersion(t, "hmac-key", "ed25519")
+	verifyExportsCorrectVersion(t, "hmac-key", "hmac")
 }
 
 func verifyExportsCorrectVersion(t *testing.T, exportType, keyType string) {
@@ -40,6 +41,9 @@ func verifyExportsCorrectVersion(t *testing.T, exportType, keyType string) {
 		"exportable": true,
 		"type":       keyType,
 	}
+	if keyType == "hmac" {
+		req.Data["key_size"] = 32
+	}
 	_, err := b.HandleRequest(context.Background(), req)
 	if err != nil {
 		t.Fatal(err)

changelog/20864.txt

@@ -0,0 +1,5 @@
+```release-note:bug
+secrets/transit: Fix export of HMAC-only key, correctly exporting the key used for sign operations. For consumers of the previously incorrect key, use the plaintext export to retrieve these incorrect keys and import them as new versions.
+secrets/transit: Fix bug related to shorter dedicated HMAC key sizing.
+sdk/helper/keysutil: New HMAC type policies will have HMACKey equal to Key and be copied over on import.
+```

sdk/helper/keysutil/policy.go

@@ -731,6 +731,10 @@ func (p *Policy) Upgrade(ctx context.Context, storage logical.Storage, randReade
 		entry.HMACKey = hmacKey
 		p.Keys[strconv.Itoa(p.LatestVersion)] = entry
 		persistNeeded = true
+
+		if p.Type == KeyType_HMAC {
+			entry.HMACKey = entry.Key
+		}
 	}
 
 	if persistNeeded {
@@ -1417,6 +1421,7 @@ func (p *Policy) Import(ctx context.Context, storage logical.Storage, key []byte
 		entry.Key = key
 		if p.Type == KeyType_HMAC {
 			p.KeySize = len(key)
+			entry.HMACKey = key
 		}
 	} else {
 		parsedPrivateKey, err := x509.ParsePKCS8PrivateKey(key)
@@ -1574,7 +1579,7 @@ func (p *Policy) RotateInMemory(randReader io.Reader) (retErr error) {
 		if p.Type == KeyType_AES128_GCM96 {
 			numBytes = 16
 		} else if p.Type == KeyType_HMAC {
-			numBytes := p.KeySize
+			numBytes = p.KeySize
 			if numBytes < HmacMinKeySize || numBytes > HmacMaxKeySize {
 				return fmt.Errorf("invalid key size for HMAC key, must be between %d and %d bytes", HmacMinKeySize, HmacMaxKeySize)
 			}
@@ -1585,6 +1590,11 @@ func (p *Policy) RotateInMemory(randReader io.Reader) (retErr error) {
 		}
 		entry.Key = newKey
 
+		if p.Type == KeyType_HMAC {
+			// To avoid causing problems, ensure HMACKey = Key.
+			entry.HMACKey = newKey
+		}
+
 	case KeyType_ECDSA_P256, KeyType_ECDSA_P384, KeyType_ECDSA_P521:
 		var curve elliptic.Curve
 		switch p.Type {