Split into FS and File

4 files changed, 423 insertions, 0 deletions

diff --git a/cryptfs/file.go b/cryptfs/file.go
new file mode 100644
index 0000000..77262d4
--- /dev/null
+++ b/cryptfs/file.go
@@ -0,0 +1,148 @@
+package cryptfs
+
+import (
+	"fmt"
+	"os"
+	"io"
+	"errors"
+	"crypto/cipher"
+)
+
+type File struct {
+	file *os.File
+	gcm cipher.AEAD
+	plainBS	int64
+	cipherBS int64
+}
+
+// readCipherBlock - Read ciphertext block number "blockNo", decrypt,
+// return plaintext
+func (be *File) readCipherBlock(blockNo int64) ([]byte, error) {
+	off := blockNo * int64(be.cipherBS)
+	buf := make([]byte, be.cipherBS)
+
+	readN, err := be.file.ReadAt(buf, off)
+
+	if err != nil && err != io.EOF {
+		return nil, err
+	}
+
+	// Truncate buffer to actually read bytes
+	buf = buf[:readN]
+
+	// Empty block?file:///home/jakob/go/src/github.com/rfjakob/gocryptfs-bazil/backend/backend.go
+
+	if len(buf) == 0 {
+		return buf, nil
+	}
+
+	if len(buf) < NONCE_LEN {
+		warn.Printf("readCipherBlock: Block is too short: %d bytes\n", len(buf))
+		return nil, errors.New("Block is too short")
+	}
+
+	// Extract nonce
+	nonce := buf[:NONCE_LEN]
+	buf = buf[NONCE_LEN:]
+
+	// Decrypt
+	var plainBuf []byte
+	plainBuf, err = be.gcm.Open(plainBuf, nonce, buf, nil)
+	if err != nil {
+		fmt.Printf("gcm.Open() failed: %d\n", err)
+		return nil, err
+	}
+
+	return plainBuf, nil
+}
+
+// intraBlock identifies a part of a file block
+type intraBlock struct {
+	blockNo int64  // Block number in file
+	offset  int64  // Offset into block plaintext
+	length  int64  // Length of data from this block
+}
+
+// Split a plaintext byte range into (possible partial) blocks
+func (be *File) splitRange(offset int64, length int64) []intraBlock {
+	var b intraBlock
+	var parts []intraBlock
+
+	for length > 0 {
+		b.blockNo = offset / be.plainBS
+		b.offset = offset % be.plainBS
+		b.length = be.min64(length, be.plainBS - b.offset)
+		parts = append(parts, b)
+		offset += b.length
+		length -= b.length
+	}
+	return parts
+}
+
+func (be *File) min64(x int64, y int64) int64 {
+	if x < y {
+		return x
+	}
+	return y
+}
+
+// writeCipherBlock - Encrypt plaintext and write it to file block "blockNo"
+func (be *File) writeCipherBlock(blockNo int64, plain []byte) error {
+
+	if int64(len(plain)) > be.plainBS {
+		panic("writeCipherBlock: Cannot write block that is larger than plainBS")
+	}
+
+	// Get fresh nonce
+	nonce := gcmNonce.Get()
+	// Encrypt data and append to nonce
+	cipherBuf := be.gcm.Seal(nonce, nonce, plain, nil)
+
+	// WriteAt retries short writes autmatically
+	written, err := be.file.WriteAt(cipherBuf, blockNo * be.cipherBS)
+
+	debug.Printf("writeCipherBlock: wrote %d ciphertext bytes to block %d\n",
+		written, blockNo)
+
+	return err
+}
+
+// Perform RMW cycle on block
+// Write "data" into file location specified in "b"
+func (be *File) rmwWrite(b intraBlock, data []byte, f *os.File) error {
+	if b.length != int64(len(data)) {
+		panic("Length mismatch")
+	}
+
+	oldBlock, err := be.readCipherBlock(b.blockNo)
+	if err != nil {
+		return err
+	}
+	newBlockLen := b.offset + b.length
+	debug.Printf("newBlockLen := %d + %d\n", b.offset, b.length)
+	var newBlock []byte
+
+	// Write goes beyond the old block and grows the file?
+	// Must create a bigger newBlock
+	if newBlockLen > int64(len(oldBlock)) {
+		newBlock = make([]byte, newBlockLen)
+	} else {
+		newBlock = make([]byte, len(oldBlock))
+	}
+
+	// Fill with old data
+	copy(newBlock, oldBlock)
+	// Then overwrite the relevant parts with new data
+	copy(newBlock[b.offset:b.offset + b.length], data)
+
+	// Actual write
+	err = be.writeCipherBlock(b.blockNo, newBlock)
+
+	if err != nil {
+		// An incomplete write to a ciphertext block means that the whole block
+		// is destroyed.
+		fmt.Printf("rmwWrite: Write error: %s\n", err)
+	}
+
+	return err
+}
diff --git a/cryptfs/fs.go b/cryptfs/fs.go
new file mode 100644
index 0000000..b40dcf3
--- /dev/null
+++ b/cryptfs/fs.go
@@ -0,0 +1,201 @@
+package cryptfs
+
+import (
+	"crypto/cipher"
+	"crypto/aes"
+	"fmt"
+	"strings"
+	"encoding/base64"
+	"errors"
+	"os"
+)
+
+const (
+	NONCE_LEN = 12
+	AUTH_TAG_LEN = 16
+	DEFAULT_PLAINBS = 4096
+
+	ENCRYPT = true
+	DECRYPT = false
+)
+
+type FS struct {
+	blockCipher cipher.Block
+	gcm cipher.AEAD
+	plainBS	int64
+	cipherBS int64
+}
+
+func New(key [16]byte) *FS {
+
+	b, err := aes.NewCipher(key[:])
+	if err != nil {
+		panic(err)
+	}
+
+	g, err := cipher.NewGCM(b)
+	if err != nil {
+		panic(err)
+	}
+
+	return &FS{
+		blockCipher: b,
+		gcm: g,
+		plainBS: DEFAULT_PLAINBS,
+		cipherBS: DEFAULT_PLAINBS + NONCE_LEN + AUTH_TAG_LEN,
+	}
+}
+
+func (fs *FS) NewFile(f *os.File) *File {
+	return &File {
+		file: f,
+		gcm: fs.gcm,
+		plainBS: fs.plainBS,
+		cipherBS: fs.cipherBS,
+	}
+}
+
+// DecryptName - decrypt filename
+func (be *FS) decryptName(cipherName string) (string, error) {
+
+	bin, err := base64.URLEncoding.DecodeString(cipherName)
+	if err != nil {
+		return "", err
+	}
+
+	if len(bin) % aes.BlockSize != 0 {
+		return "", errors.New(fmt.Sprintf("Name len=%d is not a multiple of 16", len(bin)))
+	}
+
+	iv := make([]byte, aes.BlockSize) // TODO ?
+	cbc := cipher.NewCBCDecrypter(be.blockCipher, iv)
+	cbc.CryptBlocks(bin, bin)
+
+	bin, err = be.unPad16(bin)
+	if err != nil {
+		return "", err
+	}
+
+	plain := string(bin)
+	return plain, err
+}
+
+// EncryptName - encrypt filename
+func (be *FS) encryptName(plainName string) string {
+
+	bin := []byte(plainName)
+	bin = be.pad16(bin)
+
+	iv := make([]byte, 16) // TODO ?
+	cbc := cipher.NewCBCEncrypter(be.blockCipher, iv)
+	cbc.CryptBlocks(bin, bin)
+
+	cipherName64 := base64.URLEncoding.EncodeToString(bin)
+
+	return cipherName64
+}
+
+// TranslatePath - encrypt or decrypt path. Just splits the string on "/"
+// and hands the parts to EncryptName() / DecryptName()
+func (be *FS) translatePath(path string, op bool) (string, error) {
+	var err error
+
+	// Empty string means root directory
+	if path == "" {
+		return path, err
+	}
+
+	// Run operation on each path component
+	var translatedParts []string
+	parts := strings.Split(path, "/")
+	for _, part := range parts {
+		var newPart string
+		if op == ENCRYPT {
+			newPart = be.encryptName(part)
+		} else {
+			newPart, err = be.decryptName(part)
+			if err != nil {
+				return "", err
+			}
+		}
+		translatedParts = append(translatedParts, newPart)
+	}
+
+	return strings.Join(translatedParts, "/"), err
+}
+
+// EncryptPath - encrypt filename or path. Just hands it to TranslatePath().
+func (be *FS) EncryptPath(path string) string {
+	newPath, _ := be.translatePath(path, ENCRYPT)
+	return newPath
+}
+
+// DecryptPath - decrypt filename or path. Just hands it to TranslatePath().
+func (be *FS) DecryptPath(path string) (string, error) {
+	return be.translatePath(path, DECRYPT)
+}
+
+// plainSize - calculate plaintext size from ciphertext size
+func (be *FS) PlainSize(s int64) int64 {
+	// Zero sized files stay zero-sized
+	if s > 0 {
+		// Number of blocks
+		n := s / be.cipherBS + 1
+		overhead := be.cipherBS - be.plainBS
+		s -= n * overhead
+	}
+	return s
+}
+
+// pad16 - pad filename to 16 byte blocks using standard PKCS#7 padding
+// https://tools.ietf.org/html/rfc5652#section-6.3
+func (be *FS) pad16(orig []byte) (padded []byte) {
+	oldLen := len(orig)
+	if oldLen == 0 {
+		panic("Padding zero-length string makes no sense")
+	}
+	padLen := aes.BlockSize - oldLen % aes.BlockSize
+	if padLen == 0 {
+		padLen = aes.BlockSize
+	}
+	newLen := oldLen + padLen
+	padded = make([]byte, newLen)
+	copy(padded, orig)
+	padByte := byte(padLen)
+	for i := oldLen; i < newLen; i++ {
+		padded[i] = padByte
+	}
+	return padded
+}
+
+// unPad16 - remove padding
+func (be *FS) unPad16(orig []byte) ([]byte, error) {
+	oldLen := len(orig)
+	if oldLen % aes.BlockSize != 0 {
+		return nil, errors.New("Unaligned size")
+	}
+	// The last byte is always a padding byte
+	padByte := orig[oldLen -1]
+	// The padding byte's value is the padding length
+	padLen := int(padByte)
+	// Padding must be at least 1 byte
+	if padLen <= 0 {
+		return nil, errors.New("Padding cannot be zero-length")
+	}
+	// Larger paddings make no sense
+	if padLen > aes.BlockSize {
+		return nil, errors.New("Padding cannot be larger than 16")
+	}
+	// All padding bytes must be identical
+	for i := oldLen - padLen; i < oldLen; i++ {
+		if orig[i] != padByte {
+			return nil, errors.New(fmt.Sprintf("Padding byte at i=%d is invalid", i))
+		}
+	}
+	newLen := oldLen - padLen
+	// Padding an empty string makes no sense
+	if newLen == 0 {
+		return nil, errors.New("Unpadded length is zero")
+	}
+	return orig[0:newLen], nil
+}
diff --git a/cryptfs/log.go b/cryptfs/log.go
new file mode 100644
index 0000000..947b1c3
--- /dev/null
+++ b/cryptfs/log.go
@@ -0,0 +1,19 @@
+package cryptfs
+
+import (
+	"fmt"
+)
+
+type logChannel struct {
+	enabled bool
+}
+
+func (l logChannel) Printf(format string, args ...interface{}) {
+	if l.enabled == true {
+		fmt.Printf(format, args...)
+	}
+}
+
+
+var debug = logChannel{true}
+var warn = logChannel{true}
diff --git a/cryptfs/nonce.go b/cryptfs/nonce.go
new file mode 100644
index 0000000..3803b8c
--- /dev/null
+++ b/cryptfs/nonce.go
@@ -0,0 +1,55 @@
+package cryptfs
+
+import (
+	"encoding/binary"
+	"encoding/hex"
+	"sync"
+	"crypto/rand"
+)
+
+type nonce96 struct {
+	lock sync.Mutex
+	high32 uint32
+	low64 uint64
+	ready int
+}
+
+var gcmNonce nonce96
+
+func (n *nonce96) randBytes(len int) []byte {
+	b := make([]byte, len)
+	_, err := rand.Read(b)
+	if err != nil {
+		panic("Could not get random bytes for nonce")
+	}
+	return b
+}
+
+func (n *nonce96) init() {
+	b := n.randBytes(8)
+	n.low64 = binary.BigEndian.Uint64(b)
+	b = n.randBytes(4)
+	n.high32 = binary.BigEndian.Uint32(b)
+	n.ready = 1
+	return
+}
+
+func (n *nonce96) Get() []byte {
+	n.lock.Lock()
+	if n.ready == 0 {
+		n.init()
+	}
+	n.low64++
+	if n.low64 == 0 {
+		// Counter has wrapped
+		n.high32++
+	}
+	r := make([]byte, 12)
+	binary.BigEndian.PutUint32(r[0:4], n.high32)
+	binary.BigEndian.PutUint64(r[4:12], n.low64)
+	n.lock.Unlock()
+
+	debug.Printf("nonce96.Get(): %s\n", hex.EncodeToString(r))
+
+	return r
+}