/
commands.go
209 lines (185 loc) · 5.18 KB
/
commands.go
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package pnglib
import (
"bytes"
"encoding/binary"
"encoding/hex"
"fmt"
"hash/crc32"
"log"
"strconv"
"strings"
"github.com/blackhat-go/bhg/ch-13/imgInject/models"
"github.com/blackhat-go/bhg/ch-13/imgInject/utils"
)
const (
endChunkType = "IEND"
)
//Header holds the first byte (aka magic byte)
type Header struct {
Header uint64 // 0:8
}
//Chunk represents a data byte chunk
type Chunk struct {
Size uint32
Type uint32
Data []byte
CRC uint32
}
//MetaChunk inherits a Chunk struct
type MetaChunk struct {
Chk Chunk
Offset int64
}
//ProcessImage is the wrapper to parse PNG bytes
func (mc *MetaChunk) ProcessImage(b *bytes.Reader, c *models.CmdLineOpts) {
mc.validate(b)
if (c.Offset != "") && (c.Encode == false && c.Decode == false) {
var m MetaChunk
m.Chk.Data = []byte(c.Payload)
m.Chk.Type = m.strToInt(c.Type)
m.Chk.Size = m.createChunkSize()
m.Chk.CRC = m.createChunkCRC()
bm := m.marshalData()
bmb := bm.Bytes()
fmt.Printf("Payload Original: % X\n", []byte(c.Payload))
fmt.Printf("Payload: % X\n", m.Chk.Data)
utils.WriteData(b, c, bmb)
}
if (c.Offset != "") && c.Encode {
var m MetaChunk
m.Chk.Data = utils.XorEncode([]byte(c.Payload), c.Key)
m.Chk.Type = m.strToInt(c.Type)
m.Chk.Size = m.createChunkSize()
m.Chk.CRC = m.createChunkCRC()
bm := m.marshalData()
bmb := bm.Bytes()
fmt.Printf("Payload Original: % X\n", []byte(c.Payload))
fmt.Printf("Payload Encode: % X\n", m.Chk.Data)
utils.WriteData(b, c, bmb)
}
if (c.Offset != "") && c.Decode {
var m MetaChunk
offset, _ := strconv.ParseInt(c.Offset, 10, 64)
b.Seek(offset, 0)
m.readChunk(b)
origData := m.Chk.Data
m.Chk.Data = utils.XorDecode(m.Chk.Data, c.Key)
m.Chk.CRC = m.createChunkCRC()
bm := m.marshalData()
bmb := bm.Bytes()
fmt.Printf("Payload Original: % X\n", origData)
fmt.Printf("Payload Decode: % X\n", m.Chk.Data)
utils.WriteData(b, c, bmb)
}
if c.Meta {
count := 1 //Start at 1 because 0 is reserved for magic byte
var chunkType string
for chunkType != endChunkType {
mc.getOffset(b)
mc.readChunk(b)
fmt.Println("---- Chunk # " + strconv.Itoa(count) + " ----")
fmt.Printf("Chunk Offset: %#02x\n", mc.Offset)
fmt.Printf("Chunk Length: %s bytes\n", strconv.Itoa(int(mc.Chk.Size)))
fmt.Printf("Chunk Type: %s\n", mc.chunkTypeToString())
fmt.Printf("Chunk Importance: %s\n", mc.checkCritType())
if c.Suppress == false {
fmt.Printf("Chunk Data: %#x\n", mc.Chk.Data)
} else if c.Suppress {
fmt.Printf("Chunk Data: %s\n", "Suppressed")
}
fmt.Printf("Chunk CRC: %x\n", mc.Chk.CRC)
chunkType = mc.chunkTypeToString()
count++
}
}
}
func (mc *MetaChunk) marshalData() *bytes.Buffer {
bytesMSB := new(bytes.Buffer)
if err := binary.Write(bytesMSB, binary.BigEndian, mc.Chk.Size); err != nil {
log.Fatal(err)
}
if err := binary.Write(bytesMSB, binary.BigEndian, mc.Chk.Type); err != nil {
log.Fatal(err)
}
if err := binary.Write(bytesMSB, binary.BigEndian, mc.Chk.Data); err != nil {
log.Fatal(err)
}
if err := binary.Write(bytesMSB, binary.BigEndian, mc.Chk.CRC); err != nil {
log.Fatal(err)
}
return bytesMSB
}
func (mc *MetaChunk) readChunk(b *bytes.Reader) {
mc.readChunkSize(b)
mc.readChunkType(b)
mc.readChunkBytes(b, mc.Chk.Size)
mc.readChunkCRC(b)
}
func (mc *MetaChunk) readChunkSize(b *bytes.Reader) {
if err := binary.Read(b, binary.BigEndian, &mc.Chk.Size); err != nil {
log.Fatal(err)
}
}
func (mc *MetaChunk) readChunkType(b *bytes.Reader) {
if err := binary.Read(b, binary.BigEndian, &mc.Chk.Type); err != nil {
log.Fatal(err)
}
}
func (mc *MetaChunk) readChunkBytes(b *bytes.Reader, cLen uint32) {
mc.Chk.Data = make([]byte, cLen)
if err := binary.Read(b, binary.BigEndian, &mc.Chk.Data); err != nil {
log.Fatal(err)
}
}
func (mc *MetaChunk) readChunkCRC(b *bytes.Reader) {
if err := binary.Read(b, binary.BigEndian, &mc.Chk.CRC); err != nil {
log.Fatal(err)
}
}
func (mc *MetaChunk) getOffset(b *bytes.Reader) {
offset, _ := b.Seek(0, 1)
mc.Offset = offset
}
func (mc *MetaChunk) chunkTypeToString() string {
h := fmt.Sprintf("%x", mc.Chk.Type)
decoded, _ := hex.DecodeString(h)
result := fmt.Sprintf("%s", decoded)
return result
}
func (mc *MetaChunk) checkCritType() string {
fChar := string([]rune(mc.chunkTypeToString())[0])
if fChar == strings.ToUpper(fChar) {
return "Critical"
}
return "Ancillary"
}
func (mc *MetaChunk) validate(b *bytes.Reader) {
var header Header
if err := binary.Read(b, binary.BigEndian, &header.Header); err != nil {
log.Fatal(err)
}
bArr := make([]byte, 8)
binary.BigEndian.PutUint64(bArr, header.Header)
if string(bArr[1:4]) != "PNG" {
log.Fatal("Provided file is not a valid PNG format")
} else {
fmt.Println("Valid PNG so let us continue!")
}
}
func (mc *MetaChunk) createChunkSize() uint32 {
return uint32(len(mc.Chk.Data))
}
func (mc *MetaChunk) createChunkCRC() uint32 {
bytesMSB := new(bytes.Buffer)
if err := binary.Write(bytesMSB, binary.BigEndian, mc.Chk.Type); err != nil {
log.Fatal(err)
}
if err := binary.Write(bytesMSB, binary.BigEndian, mc.Chk.Data); err != nil {
log.Fatal(err)
}
return crc32.ChecksumIEEE(bytesMSB.Bytes())
}
func (mc *MetaChunk) strToInt(s string) uint32 {
t := []byte(s)
return binary.BigEndian.Uint32(t)
}