diff options
| -rw-r--r-- | backend.go | 42 | ||||
| -rw-r--r-- | backend_content.go | 140 | ||||
| -rw-r--r-- | backend_metadata.go | 155 | ||||
| -rw-r--r-- | backend_nonce.go | 55 | ||||
| -rw-r--r-- | log.go | 19 |
5 files changed, 411 insertions, 0 deletions
diff --git a/backend.go b/backend.go new file mode 100644 index 0000000..ad80b9a --- /dev/null +++ b/backend.go @@ -0,0 +1,42 @@ +package gocryptfs + +import ( + "crypto/cipher" + "crypto/aes" +) + +const ( + NONCE_LEN = 12 + AUTH_TAG_LEN = 16 + DEFAULT_PLAINBS = 4096 + + ENCRYPT = true + DECRYPT = false +) + +type Backend struct { + blockCipher cipher.Block + gcm cipher.AEAD + plainBS int64 + cipherBS int64 +} + +func New(key [16]byte) *Backend { + + b, err := aes.NewCipher(key[:]) + if err != nil { + panic(err) + } + + g, err := cipher.NewGCM(b) + if err != nil { + panic(err) + } + + return &Backend{ + blockCipher: b, + gcm: g, + plainBS: DEFAULT_PLAINBS, + cipherBS: DEFAULT_PLAINBS + NONCE_LEN + AUTH_TAG_LEN, + } +} diff --git a/backend_content.go b/backend_content.go new file mode 100644 index 0000000..3cf2a87 --- /dev/null +++ b/backend_content.go @@ -0,0 +1,140 @@ +package gocryptfs + +import ( + "fmt" + "os" + "io" + "errors" +) + +// readCipherBlock - Read ciphertext block number "blockNo", decrypt, +// return plaintext +func (be *Backend) readCipherBlock(blockNo int64, f *os.File) ([]byte, error) { + off := blockNo * int64(be.cipherBS) + buf := make([]byte, be.cipherBS) + + readN, err := f.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 *Backend) splitRange(offset int64, length int64, f *os.File) []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 *Backend) 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 *Backend) writeCipherBlock(blockNo int64, plain []byte, f *os.File) 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 := f.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 *Backend) rmwWrite(b intraBlock, data []byte, f *os.File) error { + if b.length != int64(len(data)) { + panic("Length mismatch") + } + + oldBlock, err := be.readCipherBlock(b.blockNo, f) + 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, f) + + 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/backend_metadata.go b/backend_metadata.go new file mode 100644 index 0000000..9d2e556 --- /dev/null +++ b/backend_metadata.go @@ -0,0 +1,155 @@ +package gocryptfs + +import ( + "errors" + "fmt" + "strings" + "encoding/base64" + "crypto/cipher" + "crypto/aes" +) + +// DecryptName - decrypt filename +func (be *Backend) 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 *Backend) 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 *Backend) 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 *Backend) EncryptPath(path string) string { + newPath, _ := be.translatePath(path, ENCRYPT) + return newPath +} + +// DecryptPath - decrypt filename or path. Just hands it to TranslatePath(). +func (be *Backend) DecryptPath(path string) (string, error) { + return be.translatePath(path, DECRYPT) +} + +// plainSize - calculate plaintext size from ciphertext size +func (be *Backend) 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 *Backend) 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 *Backend) 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/backend_nonce.go b/backend_nonce.go new file mode 100644 index 0000000..835a80f --- /dev/null +++ b/backend_nonce.go @@ -0,0 +1,55 @@ +package gocryptfs + +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 +} @@ -0,0 +1,19 @@ +package gocryptfs + +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} |