feat: Encrypt header by embedding it to prevent metadata sniffing

cmd/stbak/cmd/archive.go

@@ -6,6 +6,7 @@ import (
 	"compress/gzip"
 	"context"
 	"encoding/base32"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -421,27 +422,27 @@ func encryptHeader(
 	encryptionFormat string,
 	pubkey []byte,
 ) error {
-	var err error
+	if encryptionFormat == encryptionFormatNoneKey {
+		return nil
+	}
 
-	hdr.Name, err = encryptString(hdr.Name, encryptionFormat, pubkey)
+	newHdr := &tar.Header{
+		Format:     tar.FormatPAX,
+		Size:       hdr.Size,
+		PAXRecords: map[string]string{},
+	}
+
+	wrappedHeader, err := json.Marshal(hdr)
 	if err != nil {
 		return err
 	}
 
-	hdr.Linkname, err = encryptString(hdr.Linkname, encryptionFormat, pubkey)
+	newHdr.PAXRecords[pax.STFSEmbeddedHeader], err = encryptString(string(wrappedHeader), encryptionFormat, pubkey)
 	if err != nil {
 		return err
 	}
 
-	hdr.Uname, err = encryptString(hdr.Uname, encryptionFormat, pubkey)
-	if err != nil {
-		return err
-	}
-
-	hdr.Gname, err = encryptString(hdr.Gname, encryptionFormat, pubkey)
-	if err != nil {
-		return err
-	}
+	*hdr = *newHdr
 
 	return nil
 }

cmd/stbak/cmd/recovery_fetch.go

@@ -7,6 +7,8 @@ import (
 	"compress/gzip"
 	"context"
 	"encoding/base32"
+	"encoding/json"
+	"errors"
 	"io"
 	"os"
 	"path/filepath"
@@ -20,6 +22,7 @@ import (
 	"github.com/pierrec/lz4/v4"
 	"github.com/pojntfx/stfs/pkg/controllers"
 	"github.com/pojntfx/stfs/pkg/formatting"
+	"github.com/pojntfx/stfs/pkg/pax"
 	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
 	"github.com/volatiletech/sqlboiler/v4/boil"
@@ -32,6 +35,10 @@ const (
 	previewFlag = "preview"
 )
 
+var (
+	errEmbeddedHeaderMissing = errors.New("embedded header is missing")
+)
+
 var recoveryFetchCmd = &cobra.Command{
 	Use:   "fetch",
 	Short: "Fetch a file or directory from tape or tar file by record and block",
@@ -237,27 +244,30 @@ func decryptHeader(
 	encryptionFormat string,
 	privkey []byte,
 ) error {
-	var err error
+	if encryptionFormat == encryptionFormatNoneKey {
+		return nil
+	}
 
-	hdr.Name, err = decryptString(hdr.Name, encryptionFormat, privkey)
+	if hdr.PAXRecords == nil {
+		return errEmbeddedHeaderMissing
+	}
+
+	encryptedEmbeddedHeader, ok := hdr.PAXRecords[pax.STFSEmbeddedHeader]
+	if !ok {
+		return errEmbeddedHeaderMissing
+	}
+
+	embeddedHeader, err := decryptString(encryptedEmbeddedHeader, encryptionFormat, privkey)
 	if err != nil {
 		return err
 	}
 
-	hdr.Linkname, err = decryptString(hdr.Linkname, encryptionFormat, privkey)
-	if err != nil {
+	var newHdr tar.Header
+	if err := json.Unmarshal([]byte(embeddedHeader), &newHdr); err != nil {
 		return err
 	}
 
-	hdr.Uname, err = decryptString(hdr.Uname, encryptionFormat, privkey)
-	if err != nil {
-		return err
-	}
-
-	hdr.Gname, err = decryptString(hdr.Gname, encryptionFormat, privkey)
-	if err != nil {
-		return err
-	}
+	*hdr = newHdr
 
 	return nil
 }

pkg/pax/stfs.go

@@ -20,6 +20,8 @@ const (
 	STFSRecordReplacesName = STFSPrefix + "ReplacesName"
 
 	STFSRecordUncompressedSize = STFSPrefix + "UncompressedSize"
+
+	STFSEmbeddedHeader = STFSPrefix + "EmbeddedHeader"
 )
 
 var (