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Diffstat (limited to 'cryptfs/fs.go')
-rw-r--r--cryptfs/fs.go201
1 files changed, 201 insertions, 0 deletions
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
+}