hardcoresushi/libgocryptfs
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reverse: use per-purpose nonce generation

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Also pull all the deterministic nonce code into fusefrontend_reverse
to greatly simplify the normal code path.
This commit is contained in:
Jakob Unterwurzacher 2016-09-29 21:29:45 +02:00
parent bce96b5095
commit a2510efe12
9 changed files with 71 additions and 52 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
internal/configfile/config_file.go
View File

@ -168,7 +168,7 @@ func (cf *ConfFile) EncryptKey(key []byte, password string, logN int) {
// Lock master key using password-based key
cc := cryptocore.New(scryptHash, cryptocore.BackendGoGCM, 96)
ce := contentenc.New(cc, 4096)
cf.EncryptedKey = ce.EncryptBlock(key, 0, nil, contentenc.RandomNonce, nil)
cf.EncryptedKey = ce.EncryptBlock(key, 0, nil)
}
// WriteFile - write out config in JSON format to file "filename.tmp"

60
internal/contentenc/content.go
View File

@ -127,50 +127,34 @@ func (be *ContentEnc) DecryptBlock(ciphertext []byte, blockNo uint64, fileId []b
return plaintext, nil
}
// EncryptBlocks - Encrypt a number of blocks
// Used for reverse mode
func (be *ContentEnc) EncryptBlocks(plaintext []byte, firstBlockNo uint64, fileId []byte, nMode NonceMode) []byte {
inBuf := bytes.NewBuffer(plaintext)
var outBuf bytes.Buffer
for blockNo := firstBlockNo; inBuf.Len() > 0; blockNo++ {
inBlock := inBuf.Next(int(be.plainBS))
outBlock := be.EncryptBlock(inBlock, blockNo, fileId, nMode, nil)
outBuf.Write(outBlock)
}
return outBuf.Bytes()
// EncryptBlock - Encrypt plaintext using a random nonce.
// blockNo and fileID are used as associated data.
// The output is nonce + ciphertext + tag.
func (be *ContentEnc) EncryptBlock(plaintext []byte, blockNo uint64, fileID []byte) []byte {
// Get a fresh random nonce
nonce := be.cryptoCore.IVGenerator.Get()
return be.doEncryptBlock(plaintext, blockNo, fileID, nonce)
}
// encryptBlock - Encrypt and add IV and MAC
func (be *ContentEnc) EncryptBlock(plaintext []byte, blockNo uint64, fileID []byte, nMode NonceMode, externalNonce []byte) []byte {
// EncryptBlockNonce - Encrypt plaintext using a nonce chosen by the caller.
// blockNo and fileID are used as associated data.
// The output is nonce + ciphertext + tag.
// This function can only be used in SIV mode.
func (be *ContentEnc) EncryptBlockNonce(plaintext []byte, blockNo uint64, fileID []byte, nonce []byte) []byte {
if be.cryptoCore.AEADBackend != cryptocore.BackendAESSIV {
panic("deterministic nonces are only secure in SIV mode")
}
return be.doEncryptBlock(plaintext, blockNo, fileID, nonce)
}
// doEncryptBlock is the backend for EncryptBlock and EncryptBlockNonce.
// blockNo and fileID are used as associated data.
// The output is nonce + ciphertext + tag.
func (be *ContentEnc) doEncryptBlock(plaintext []byte, blockNo uint64, fileID []byte, nonce []byte) []byte {
// Empty block?
if len(plaintext) == 0 {
return plaintext
}
var nonce []byte
switch nMode {
case ExternalNonce:
if be.cryptoCore.AEADBackend != cryptocore.BackendAESSIV {
panic("MUST NOT use deterministic nonces unless in AESSIV mode!")
}
nonce = externalNonce
case ReverseDeterministicNonce:
if be.cryptoCore.AEADBackend != cryptocore.BackendAESSIV {
panic("MUST NOT use deterministic nonces unless in AESSIV mode!")
}
l := be.cryptoCore.IVLen
nonce = make([]byte, l)
copy(nonce, fileID)
// Add the block number to the last 8 byte. Plus one so the block-zero
// IV is distinct from the fileID.
counter := binary.BigEndian.Uint64(nonce[l-8 : l])
binary.BigEndian.PutUint64(nonce[l-8:l], counter+blockNo+1)
case RandomNonce:
// Get a fresh random nonce
nonce = be.cryptoCore.IVGenerator.Get()
default:
panic("invalid nonce mode")
}
if len(nonce) != be.cryptoCore.IVLen {
panic("wrong nonce length")
}

2
internal/fusefrontend/file.go
View File

@ -256,7 +256,7 @@ func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) {
// Encrypt
blockOffset := b.BlockCipherOff()
blockData = f.contentEnc.EncryptBlock(blockData, b.BlockNo, f.header.Id, contentenc.RandomNonce, nil)
blockData = f.contentEnc.EncryptBlock(blockData, b.BlockNo, f.header.Id)
tlog.Debug.Printf("ino%d: Writing %d bytes to block #%d",
f.ino, uint64(len(blockData))-f.contentEnc.BlockOverhead(), b.BlockNo)

2
internal/fusefrontend/fs.go
View File

@ -326,7 +326,7 @@ func (fs *FS) Symlink(target string, linkName string, context *fuse.Context) (co
return fuse.ToStatus(err)
}
// Symlinks are encrypted like file contents (GCM) and base64-encoded
cBinTarget := fs.contentEnc.EncryptBlock([]byte(target), 0, nil, contentenc.RandomNonce, nil)
cBinTarget := fs.contentEnc.EncryptBlock([]byte(target), 0, nil)
cTarget := base64.URLEncoding.EncodeToString(cBinTarget)
// Handle long file name

2
internal/fusefrontend_reverse/reverse_longnames.go
View File

@ -84,7 +84,7 @@ func (rfs *reverseFS) newNameFile(relPath string) (nodefs.File, fuse.Status) {
if err != nil {
return nil, fuse.ToStatus(err)
}
dirIV := derivePathIV(cDir)
dirIV := derivePathIV(cDir, ivPurposeDirIV)
e, err := rfs.findLongnameParent(pDir, dirIV, longname)
if err != nil {
return nil, fuse.ToStatus(err)

28
internal/fusefrontend_reverse/rfile.go
View File

@ -2,6 +2,7 @@ package fusefrontend_reverse
import (
"bytes"
"encoding/binary"
"fmt"
"io"
"os"
@ -20,6 +21,8 @@ type reverseFile struct {
fd *os.File
// File header (contains the IV)
header contentenc.FileHeader
// IV for block 0
block0IV []byte
// Content encryption helper
contentEnc *contentenc.ContentEnc
}
@ -33,7 +36,7 @@ func (rfs *reverseFS) NewFile(relPath string, flags uint32) (nodefs.File, fuse.S
if err != nil {
return nil, fuse.ToStatus(err)
}
id := derivePathIV(relPath)
id := derivePathIV(relPath, ivPurposeFileID)
header := contentenc.FileHeader{
Version: contentenc.CurrentVersion,
Id: id,
@ -42,6 +45,7 @@ func (rfs *reverseFS) NewFile(relPath string, flags uint32) (nodefs.File, fuse.S
File: nodefs.NewDefaultFile(),
fd: fd,
header: header,
block0IV: derivePathIV(relPath, ivPurposeBlock0IV),
contentEnc: rfs.contentEnc,
}, fuse.OK
}
@ -52,6 +56,26 @@ func (rf *reverseFile) GetAttr(*fuse.Attr) fuse.Status {
return fuse.ENOSYS
}
// encryptBlocks - encrypt "plaintext" into a number of ciphertext blocks.
// "plaintext" must already be block-aligned.
func (rf *reverseFile) encryptBlocks(plaintext []byte, firstBlockNo uint64, fileId []byte, block0IV []byte) []byte {
nonce := make([]byte, len(block0IV))
copy(nonce, block0IV)
block0IVlow := binary.BigEndian.Uint64(block0IV[8:])
nonceLow := nonce[8:]
inBuf := bytes.NewBuffer(plaintext)
var outBuf bytes.Buffer
bs := int(rf.contentEnc.PlainBS())
for blockNo := firstBlockNo; inBuf.Len() > 0; blockNo++ {
binary.BigEndian.PutUint64(nonceLow, block0IVlow+blockNo)
inBlock := inBuf.Next(bs)
outBlock := rf.contentEnc.EncryptBlockNonce(inBlock, blockNo, fileId, nonce)
outBuf.Write(outBlock)
}
return outBuf.Bytes()
}
// readBackingFile: read from the backing plaintext file, encrypt it, return the
// ciphertext.
// "off" ... ciphertext offset (must be >= HEADER_LEN)
@ -71,7 +95,7 @@ func (rf *reverseFile) readBackingFile(off uint64, length uint64) (out []byte, e
plaintext = plaintext[0:n]
// Encrypt blocks
ciphertext := rf.contentEnc.EncryptBlocks(plaintext, blocks[0].BlockNo, rf.header.Id, contentenc.ReverseDeterministicNonce)
ciphertext := rf.encryptBlocks(plaintext, blocks[0].BlockNo, rf.header.Id, rf.block0IV)
// Crop down to the relevant part
lenHave := len(ciphertext)

6
internal/fusefrontend_reverse/rfs.go
View File

@ -254,7 +254,7 @@ func (rfs *reverseFS) OpenDir(cipherPath string, context *fuse.Context) ([]fuse.
nVirtual := 1
// Encrypt names
dirIV := derivePathIV(cipherPath)
dirIV := derivePathIV(cipherPath, ivPurposeDirIV)
for i := range entries {
var cName string
// ".gocryptfs.reverse.conf" in the root directory is mapped to "gocryptfs.conf"
@ -296,9 +296,9 @@ func (rfs *reverseFS) Readlink(cipherPath string, context *fuse.Context) (string
if rfs.args.PlaintextNames {
return plainTarget, fuse.OK
}
nonce := derivePathIV(cipherPath)
nonce := derivePathIV(cipherPath, ivPurposeSymlinkIV)
// Symlinks are encrypted like file contents and base64-encoded
cBinTarget := rfs.contentEnc.EncryptBlock([]byte(plainTarget), 0, nil, contentenc.ExternalNonce, nonce)
cBinTarget := rfs.contentEnc.EncryptBlockNonce([]byte(plainTarget), 0, nil, nonce)
cTarget := base64.URLEncoding.EncodeToString(cBinTarget)
return cTarget, fuse.OK
}

19
internal/fusefrontend_reverse/rpath.go
View File

@ -19,9 +19,20 @@ func saneDir(path string) string {
return d
}
// derivePathIV derives an IV from an encrypted path by hashing it
func derivePathIV(path string) []byte {
hash := sha256.Sum256([]byte(path))
type ivPurposeType string
const (
ivPurposeDirIV ivPurposeType = "DIRIV"
ivPurposeFileID ivPurposeType = "FILEID"
ivPurposeSymlinkIV ivPurposeType = "SYMLINKIV"
ivPurposeBlock0IV ivPurposeType = "BLOCK0IV"
)
// derivePathIV derives an IV from an encrypted path by hashing it with sha256
func derivePathIV(path string, purpose ivPurposeType) []byte {
// Use null byte as separator as it cannot occour in the path
extended := []byte(path + "\000" + string(purpose))
hash := sha256.Sum256(extended)
return hash[:nametransform.DirIVLen]
}
@ -43,7 +54,7 @@ func (rfs *reverseFS) decryptPath(relPath string) (string, error) {
// Start at the top and recurse
currentDir := filepath.Join(parts[:i]...)
nameType := nametransform.NameType(part)
dirIV := derivePathIV(currentDir)
dirIV := derivePathIV(currentDir, ivPurposeDirIV)
var transformedPart string
if nameType == nametransform.LongNameNone {
transformedPart, err = rfs.nameTransform.DecryptName(part, dirIV)

2
internal/fusefrontend_reverse/virtualfile.go
View File

@ -14,7 +14,7 @@ func (rfs *reverseFS) newDirIVFile(cRelPath string) (nodefs.File, fuse.Status) {
if err != nil {
return nil, fuse.ToStatus(err)
}
return rfs.NewVirtualFile(derivePathIV(cDir), absDir)
return rfs.NewVirtualFile(derivePathIV(cDir, ivPurposeDirIV), absDir)
}
type virtualFile struct {