xray: add "gocryptfs-xray", on-disk-format exploration tool

Example output for a file encrypted in reverse mode:

Header: Version: 2, Id: 0b7f5e2574e4afa859a9bb156a2e7772
Block  0: IV: 0b7f5e2574e4afa859a9bb156a2e7773, Tag: bf39279ac6b1ccd852567aaf26ee386b, Len: 4128
Block  1: IV: 0b7f5e2574e4afa859a9bb156a2e7774, Tag: a4f0f9cde7f70a752254aa8fe7718699, Len: 4128
Block  2: IV: 0b7f5e2574e4afa859a9bb156a2e7775, Tag: b467b153016fc1d531818b65ab9e24f6, Len: 4128
Block  3: IV: 0b7f5e2574e4afa859a9bb156a2e7776, Tag: 1fcb7ffd8f1816fbe807df8148718a5c, Len: 4128
Block  4: IV: 0b7f5e2574e4afa859a9bb156a2e7777, Tag: a217e7933ef434c9f03ad931bb5fde9b, Len: 4128
Block  5: IV: 0b7f5e2574e4afa859a9bb156a2e7778, Tag: f3e6240d75cd66371a0b301111d6f1fc, Len: 4128
Block  6: IV: 0b7f5e2574e4afa859a9bb156a2e7779, Tag: bc85d322ebc7761ae5ef114ea3903a56, Len: 4128
Block  7: IV: 0b7f5e2574e4afa859a9bb156a2e777a, Tag: efda01c6b794690f939a12d6d49ac3af, Len: 4128
Block  8: IV: 0b7f5e2574e4afa859a9bb156a2e777b, Tag: b198329d489d1392080f710206932ff0, Len: 2907
This commit is contained in:
Jakob Unterwurzacher 2016-09-25 11:11:20 +02:00
parent 6c52c1a6e6
commit 3a9bd92754
3 changed files with 87 additions and 0 deletions

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@ -40,6 +40,7 @@ else
# Go 1.5 wants an "=" here
go build -ldflags="-X main.GitVersion=$GITVERSION -X main.GitVersionFuse=$GITVERSIONFUSE -X main.BuildTime=$BUILDTIME"
fi
(cd gocryptfs-xray; go build)
./gocryptfs -version

1
gocryptfs-xray/.gitignore vendored Normal file
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@ -0,0 +1 @@
gocryptfs-xray

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@ -0,0 +1,85 @@
package main
import (
"encoding/hex"
"flag"
"fmt"
"io"
"os"
"github.com/rfjakob/gocryptfs/internal/contentenc"
"github.com/rfjakob/gocryptfs/internal/cryptocore"
)
const (
IVLen = contentenc.IVBitLen / 8
blockSize = contentenc.DefaultBS + IVLen + cryptocore.AuthTagLen
)
func errExit(err error) {
fmt.Println(err)
os.Exit(1)
}
func prettyPrintHeader(h *contentenc.FileHeader) {
id := hex.EncodeToString(h.Id)
fmt.Printf("Header: Version: %d, Id: %s\n", h.Version, id)
}
func main() {
flag.Parse()
if flag.NArg() != 1 {
fmt.Printf("Usage: xray FILE\n")
os.Exit(1)
}
f := flag.Arg(0)
fd, err := os.Open(f)
if err != nil {
errExit(err)
}
headerBytes := make([]byte, contentenc.HEADER_LEN)
n, err := fd.ReadAt(headerBytes, 0)
if err == io.EOF && n == 0 {
fmt.Println("empty file")
os.Exit(0)
} else if err == io.EOF {
fmt.Printf("incomplete file header: read %d bytes, want %d\n", n, contentenc.HEADER_LEN)
os.Exit(1)
} else if err != nil {
errExit(err)
}
header, err := contentenc.ParseHeader(headerBytes)
if err != nil {
errExit(err)
}
prettyPrintHeader(header)
var i int64
for i = 0; ; i++ {
blockLen := int64(blockSize)
off := contentenc.HEADER_LEN + i*blockSize
iv := make([]byte, IVLen)
_, err := fd.ReadAt(iv, off)
if err == io.EOF {
break
} else if err != nil {
errExit(err)
}
tag := make([]byte, cryptocore.AuthTagLen)
_, err = fd.ReadAt(tag, off+blockSize-cryptocore.AuthTagLen)
if err == io.EOF {
fi, err2 := fd.Stat()
if err2 != nil {
errExit(err2)
}
_, err2 = fd.ReadAt(tag, fi.Size()-cryptocore.AuthTagLen)
if err2 != nil {
errExit(err2)
}
blockLen = (fi.Size() - contentenc.HEADER_LEN) % blockSize
} else if err != nil {
errExit(err)
}
fmt.Printf("Block %2d: IV: %s, Tag: %s, Len: %d\n", i, hex.EncodeToString(iv), hex.EncodeToString(tag), blockLen)
}
}