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authorJakob Unterwurzacher2015-11-01 01:32:33 +0100
committerJakob Unterwurzacher2015-11-01 01:38:27 +0100
commit76311b60f2e208dbd93e1e7b6e9794770c14fede (patch)
treefa71d48744fd1ad6de26aaadd03f2440e4d4103d /cryptfs/cryptfs_content.go
parent73fa8efdb27172210b9751eb86689287db0b1170 (diff)
Add file header (on-disk-format change)
Format: [ "Version" uint16 big endian ] [ "Id" 16 random bytes ] Quoting SECURITY.md: * Every file has a header that contains a 16-byte random *file id* * Each block uses the file id and its block number as GCM *authentication data* * This means the position of the blocks is protected as well. The blocks can not be reordered or copied between different files without causing an decryption error.
Diffstat (limited to 'cryptfs/cryptfs_content.go')
-rw-r--r--cryptfs/cryptfs_content.go20
1 files changed, 13 insertions, 7 deletions
diff --git a/cryptfs/cryptfs_content.go b/cryptfs/cryptfs_content.go
index 7a1859a..03253d3 100644
--- a/cryptfs/cryptfs_content.go
+++ b/cryptfs/cryptfs_content.go
@@ -30,14 +30,14 @@ type CryptFile struct {
}
// DecryptBlocks - Decrypt a number of blocks
-func (be *CryptFS) DecryptBlocks(ciphertext []byte, firstBlockNo uint64) ([]byte, error) {
+func (be *CryptFS) DecryptBlocks(ciphertext []byte, firstBlockNo uint64, fileId []byte) ([]byte, error) {
cBuf := bytes.NewBuffer(ciphertext)
var err error
var pBuf bytes.Buffer
for cBuf.Len() > 0 {
cBlock := cBuf.Next(int(be.cipherBS))
var pBlock []byte
- pBlock, err = be.DecryptBlock(cBlock, firstBlockNo)
+ pBlock, err = be.DecryptBlock(cBlock, firstBlockNo, fileId)
if err != nil {
break
}
@@ -51,7 +51,7 @@ func (be *CryptFS) DecryptBlocks(ciphertext []byte, firstBlockNo uint64) ([]byte
//
// Corner case: A full-sized block of all-zero ciphertext bytes is translated
// to an all-zero plaintext block, i.e. file hole passtrough.
-func (be *CryptFS) DecryptBlock(ciphertext []byte, blockNo uint64) ([]byte, error) {
+func (be *CryptFS) DecryptBlock(ciphertext []byte, blockNo uint64, fileId []byte) ([]byte, error) {
// Empty block?
if len(ciphertext) == 0 {
@@ -77,6 +77,7 @@ func (be *CryptFS) DecryptBlock(ciphertext []byte, blockNo uint64) ([]byte, erro
// Decrypt
var plaintext []byte
aData := make([]byte, 8)
+ aData = append(aData, fileId...)
binary.BigEndian.PutUint64(aData, blockNo)
plaintext, err := be.gcm.Open(plaintext, nonce, ciphertext, aData)
@@ -89,8 +90,8 @@ func (be *CryptFS) DecryptBlock(ciphertext []byte, blockNo uint64) ([]byte, erro
return plaintext, nil
}
-// encryptBlock - Encrypt and add MAC using GCM
-func (be *CryptFS) EncryptBlock(plaintext []byte, blockNo uint64) []byte {
+// encryptBlock - Encrypt and add IV and MAC
+func (be *CryptFS) EncryptBlock(plaintext []byte, blockNo uint64, fileId []byte) []byte {
// Empty block?
if len(plaintext) == 0 {
@@ -103,6 +104,7 @@ func (be *CryptFS) EncryptBlock(plaintext []byte, blockNo uint64) []byte {
// Encrypt plaintext and append to nonce
aData := make([]byte, 8)
binary.BigEndian.PutUint64(aData, blockNo)
+ aData = append(aData, fileId...)
ciphertext := be.gcm.Seal(nonce, nonce, plaintext, aData)
return ciphertext
@@ -118,6 +120,7 @@ func (be *CryptFS) SplitRange(offset uint64, length uint64) []intraBlock {
for length > 0 {
b.BlockNo = offset / be.plainBS
b.Skip = offset % be.plainBS
+ // Minimum of remaining data and remaining space in the block
b.Length = be.minu64(length, be.plainBS-b.Skip)
parts = append(parts, b)
offset += b.Length
@@ -134,6 +137,9 @@ func (be *CryptFS) PlainSize(size uint64) uint64 {
return 0
}
+ // Account for header
+ size -= HEADER_LEN
+
overhead := be.cipherBS - be.plainBS
nBlocks := (size + be.cipherBS - 1) / be.cipherBS
if nBlocks*overhead > size {
@@ -171,7 +177,7 @@ func (be *CryptFS) CiphertextRange(offset uint64, length uint64) (alignedOffset
firstBlockNo := offset / be.plainBS
lastBlockNo := (offset + length - 1) / be.plainBS
- alignedOffset = firstBlockNo * be.cipherBS
+ alignedOffset = HEADER_LEN + firstBlockNo * be.cipherBS
alignedLength = (lastBlockNo - firstBlockNo + 1) * be.cipherBS
skipBytes = int(skip)
@@ -232,5 +238,5 @@ func (be *CryptFS) BlockNoPlainOff(plainOffset uint64) uint64 {
// Get the block number at ciphter-text offset
func (be *CryptFS) BlockNoCipherOff(cipherOffset uint64) uint64 {
- return cipherOffset / be.cipherBS
+ return (cipherOffset - HEADER_LEN) / be.cipherBS
}