Re-design of the original gocryptfs code to work as a library.
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// Package contentenc encrypts and decrypts file blocks.
package contentenc
import (
"bytes"
"encoding/binary"
"errors"
"log"
"runtime"
"sync"
"../cryptocore"
)
const (
//value from FUSE doc
MAX_KERNEL_WRITE = 128 * 1024
// DefaultBS is the default plaintext block size
DefaultBS = 4096
// DefaultIVBits is the default length of IV, in bits.
// We always use 128-bit IVs for file content, but the
// master key in the config file is encrypted with a 96-bit IV for
// gocryptfs v1.2 and earlier. v1.3 switched to 128 bit.
DefaultIVBits = 128
)
// ContentEnc is used to encipher and decipher file content.
type ContentEnc struct {
// Cryptographic primitives
cryptoCore *cryptocore.CryptoCore
// plainBS is the plaintext block size. Usually 4096 bytes.
plainBS uint64
// cipherBS is the ciphertext block size. Usually 4128 bytes.
// `cipherBS - plainBS`is the per-block overhead
// (use BlockOverhead() to calculate it for you!)
cipherBS uint64
// All-zero block of size cipherBS, for fast compares
allZeroBlock []byte
// All-zero block of size IVBitLen/8, for fast compares
allZeroNonce []byte
// Ciphertext block "sync.Pool" pool. Always returns cipherBS-sized byte
// slices (usually 4128 bytes).
cBlockPool bPool
// Plaintext block pool. Always returns plainBS-sized byte slices
// (usually 4096 bytes).
pBlockPool bPool
// Ciphertext request data pool. Always returns byte slices of size
// fuse.MAX_KERNEL_WRITE + encryption overhead.
// Used by Read() to temporarily store the ciphertext as it is read from
// disk.
CReqPool bPool
// Plaintext request data pool. Slice have size fuse.MAX_KERNEL_WRITE.
PReqPool bPool
}
// New returns an initialized ContentEnc instance.
func New(cc *cryptocore.CryptoCore, plainBS uint64) *ContentEnc {
if MAX_KERNEL_WRITE%plainBS != 0 {
log.Panicf("unaligned MAX_KERNEL_WRITE=%d", MAX_KERNEL_WRITE)
}
cipherBS := plainBS + uint64(cc.IVLen) + cryptocore.AuthTagLen
// Take IV and GHASH overhead into account.
cReqSize := int(MAX_KERNEL_WRITE / plainBS * cipherBS)
// Unaligned reads (happens during fsck, could also happen with O_DIRECT?)
// touch one additional ciphertext and plaintext block. Reserve space for the
// extra block.
cReqSize += int(cipherBS)
pReqSize := MAX_KERNEL_WRITE + int(plainBS)
c := &ContentEnc{
cryptoCore: cc,
plainBS: plainBS,
cipherBS: cipherBS,
allZeroBlock: make([]byte, cipherBS),
allZeroNonce: make([]byte, cc.IVLen),
cBlockPool: newBPool(int(cipherBS)),
CReqPool: newBPool(cReqSize),
pBlockPool: newBPool(int(plainBS)),
PReqPool: newBPool(pReqSize),
}
return c
}
// PlainBS returns the plaintext block size
func (be *ContentEnc) PlainBS() uint64 {
return be.plainBS
}
// CipherBS returns the ciphertext block size
func (be *ContentEnc) CipherBS() uint64 {
return be.cipherBS
}
// DecryptBlocks decrypts a number of blocks
func (be *ContentEnc) DecryptBlocks(ciphertext []byte, firstBlockNo uint64, fileID []byte) ([]byte, error) {
cBuf := bytes.NewBuffer(ciphertext)
var err error
pBuf := bytes.NewBuffer(be.PReqPool.Get()[:0])
blockNo := firstBlockNo
for cBuf.Len() > 0 {
cBlock := cBuf.Next(int(be.cipherBS))
var pBlock []byte
pBlock, err = be.DecryptBlock(cBlock, blockNo, fileID)
if err != nil {
break
}
pBuf.Write(pBlock)
be.pBlockPool.Put(pBlock)
blockNo++
}
return pBuf.Bytes(), err
}
// concatAD concatenates the block number and the file ID to a byte blob
// that can be passed to AES-GCM as associated data (AD).
// Result is: aData = [blockNo.bigEndian fileID].
func concatAD(blockNo uint64, fileID []byte) (aData []byte) {
if fileID != nil && len(fileID) != headerIDLen {
// fileID is nil when decrypting the master key from the config file,
// and for symlinks and xattrs.
log.Panicf("wrong fileID length: %d", len(fileID))
}
const lenUint64 = 8
// Preallocate space to save an allocation in append()
aData = make([]byte, lenUint64, lenUint64+headerIDLen)
binary.BigEndian.PutUint64(aData, blockNo)
aData = append(aData, fileID...)
return aData
}
// DecryptBlock - Verify and decrypt GCM block
//
// Corner case: A full-sized block of all-zero ciphertext bytes is translated
// to an all-zero plaintext block, i.e. file hole passthrough.
func (be *ContentEnc) DecryptBlock(ciphertext []byte, blockNo uint64, fileID []byte) ([]byte, error) {
// Empty block?
if len(ciphertext) == 0 {
return ciphertext, nil
}
// All-zero block?
if bytes.Equal(ciphertext, be.allZeroBlock) {
return make([]byte, be.plainBS), nil
}
if len(ciphertext) < be.cryptoCore.IVLen {
return nil, errors.New("Block is too short")
}
// Extract nonce
nonce := ciphertext[:be.cryptoCore.IVLen]
if bytes.Equal(nonce, be.allZeroNonce) {
// Bug in tmpfs?
// https://github.com/rfjakob/gocryptfs/issues/56
// http://www.spinics.net/lists/kernel/msg2370127.html
return nil, errors.New("all-zero nonce")
}
ciphertext = ciphertext[be.cryptoCore.IVLen:]
// Decrypt
plaintext := be.pBlockPool.Get()
plaintext = plaintext[:0]
aData := concatAD(blockNo, fileID)
plaintext, err := be.cryptoCore.AEADCipher.Open(plaintext, nonce, ciphertext, aData)
if err != nil {
return nil, err
}
return plaintext, nil
}
// At some point, splitting the ciphertext into more groups will not improve
// performance, as spawning goroutines comes at a cost.
// 2 seems to work ok for now.
const encryptMaxSplit = 2
// encryptBlocksParallel splits the plaintext into parts and encrypts them
// in parallel.
func (be *ContentEnc) encryptBlocksParallel(plaintextBlocks [][]byte, ciphertextBlocks [][]byte, firstBlockNo uint64, fileID []byte) {
ncpu := runtime.NumCPU()
if ncpu > encryptMaxSplit {
ncpu = encryptMaxSplit
}
groupSize := len(plaintextBlocks) / ncpu
var wg sync.WaitGroup
for i := 0; i < ncpu; i++ {
wg.Add(1)
go func(i int) {
low := i * groupSize
high := (i + 1) * groupSize
if i == ncpu-1 {
// Last part picks up any left-over blocks
//
// The last part could run in the original goroutine, but
// doing that complicates the code, and, surprisingly,
// incurs a 1 % performance penalty.
high = len(plaintextBlocks)
}
be.doEncryptBlocks(plaintextBlocks[low:high], ciphertextBlocks[low:high], firstBlockNo+uint64(low), fileID)
wg.Done()
}(i)
}
wg.Wait()
}
// EncryptBlocks is like EncryptBlock but takes multiple plaintext blocks.
// Returns a byte slice from CReqPool - so don't forget to return it
// to the pool.
func (be *ContentEnc) EncryptBlocks(plaintextBlocks [][]byte, firstBlockNo uint64, fileID []byte) []byte {
ciphertextBlocks := make([][]byte, len(plaintextBlocks))
// For large writes, we parallelize encryption.
if len(plaintextBlocks) >= 32 && runtime.NumCPU() >= 2 {
be.encryptBlocksParallel(plaintextBlocks, ciphertextBlocks, firstBlockNo, fileID)
} else {
be.doEncryptBlocks(plaintextBlocks, ciphertextBlocks, firstBlockNo, fileID)
}
// Concatenate ciphertext into a single byte array.
tmp := be.CReqPool.Get()
out := bytes.NewBuffer(tmp[:0])
for _, v := range ciphertextBlocks {
out.Write(v)
// Return the memory to cBlockPool
be.cBlockPool.Put(v)
}
return out.Bytes()
}
// doEncryptBlocks is called by EncryptBlocks to do the actual encryption work
func (be *ContentEnc) doEncryptBlocks(in [][]byte, out [][]byte, firstBlockNo uint64, fileID []byte) {
for i, v := range in {
out[i] = be.EncryptBlock(v, firstBlockNo+uint64(i), fileID)
}
}
// 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)
}
// 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 {
log.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
}
if len(nonce) != be.cryptoCore.IVLen {
log.Panic("wrong nonce length")
}
// Block is authenticated with block number and file ID
aData := concatAD(blockNo, fileID)
// Get a cipherBS-sized block of memory, copy the nonce into it and truncate to
// nonce length
cBlock := be.cBlockPool.Get()
copy(cBlock, nonce)
cBlock = cBlock[0:len(nonce)]
// Encrypt plaintext and append to nonce
ciphertext := be.cryptoCore.AEADCipher.Seal(cBlock, nonce, plaintext, aData)
overhead := int(be.BlockOverhead())
if len(plaintext)+overhead != len(ciphertext) {
log.Panicf("unexpected ciphertext length: plaintext=%d, overhead=%d, ciphertext=%d",
len(plaintext), overhead, len(ciphertext))
}
return ciphertext
}
// MergeBlocks - Merge newData into oldData at offset
// New block may be bigger than both newData and oldData
func (be *ContentEnc) MergeBlocks(oldData []byte, newData []byte, offset int) []byte {
// Fastpath for small-file creation
if len(oldData) == 0 && offset == 0 {
return newData
}
// Make block of maximum size
out := make([]byte, be.plainBS)
// Copy old and new data into it
copy(out, oldData)
l := len(newData)
copy(out[offset:offset+l], newData)
// Crop to length
outLen := len(oldData)
newLen := offset + len(newData)
if outLen < newLen {
outLen = newLen
}
return out[0:outLen]
}
// Wipe tries to wipe secret keys from memory by overwriting them with zeros
// and/or setting references to nil.
func (be *ContentEnc) Wipe() {
be.cryptoCore.Wipe()
be.cryptoCore = nil
}