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authorJakob Unterwurzacher2015-09-03 18:57:28 +0200
committerJakob Unterwurzacher2015-09-03 19:09:11 +0200
commitf8fddff7694b2cb9487fd4b5cbe9f97a136600b0 (patch)
treec592e59683165d9af1116e65fa16ffddff1bb7c5 /cryptfs
parent4e93fdf820695c6afb38d525b5cf1dcc64080305 (diff)
Split into FS and File
Diffstat (limited to 'cryptfs')
-rw-r--r--cryptfs/file.go148
-rw-r--r--cryptfs/fs.go201
-rw-r--r--cryptfs/log.go19
-rw-r--r--cryptfs/nonce.go55
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
+}