149 lines
3.4 KiB
Go
149 lines
3.4 KiB
Go
package cryptfs
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import (
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"fmt"
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"os"
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"io"
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"errors"
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"crypto/cipher"
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)
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type CryptFile struct {
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file *os.File
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gcm cipher.AEAD
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plainBS int64
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cipherBS int64
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}
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// readCipherBlock - Read ciphertext block number "blockNo", decrypt,
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// return plaintext
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func (be *CryptFile) readCipherBlock(blockNo int64) ([]byte, error) {
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off := blockNo * int64(be.cipherBS)
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buf := make([]byte, be.cipherBS)
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readN, err := be.file.ReadAt(buf, off)
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if err != nil && err != io.EOF {
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return nil, err
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}
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// Truncate buffer to actually read bytes
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buf = buf[:readN]
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// Empty block?file:///home/jakob/go/src/github.com/rfjakob/gocryptfs-bazil/backend/backend.go
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if len(buf) == 0 {
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return buf, nil
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}
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if len(buf) < NONCE_LEN {
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warn.Printf("readCipherBlock: Block is too short: %d bytes\n", len(buf))
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return nil, errors.New("Block is too short")
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}
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// Extract nonce
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nonce := buf[:NONCE_LEN]
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buf = buf[NONCE_LEN:]
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// Decrypt
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var plainBuf []byte
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plainBuf, err = be.gcm.Open(plainBuf, nonce, buf, nil)
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if err != nil {
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fmt.Printf("gcm.Open() failed: %d\n", err)
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return nil, err
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}
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return plainBuf, nil
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}
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// intraBlock identifies a part of a file block
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type intraBlock struct {
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blockNo int64 // Block number in file
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offset int64 // Offset into block plaintext
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length int64 // Length of data from this block
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}
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// Split a plaintext byte range into (possible partial) blocks
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func (be *CryptFile) splitRange(offset int64, length int64) []intraBlock {
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var b intraBlock
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var parts []intraBlock
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for length > 0 {
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b.blockNo = offset / be.plainBS
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b.offset = offset % be.plainBS
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b.length = be.min64(length, be.plainBS - b.offset)
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parts = append(parts, b)
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offset += b.length
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length -= b.length
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}
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return parts
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}
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func (be *CryptFile) min64(x int64, y int64) int64 {
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if x < y {
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return x
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}
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return y
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}
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// writeCipherBlock - Encrypt plaintext and write it to file block "blockNo"
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func (be *CryptFile) writeCipherBlock(blockNo int64, plain []byte) error {
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if int64(len(plain)) > be.plainBS {
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panic("writeCipherBlock: Cannot write block that is larger than plainBS")
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}
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// Get fresh nonce
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nonce := gcmNonce.Get()
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// Encrypt data and append to nonce
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cipherBuf := be.gcm.Seal(nonce, nonce, plain, nil)
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// WriteAt retries short writes autmatically
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written, err := be.file.WriteAt(cipherBuf, blockNo * be.cipherBS)
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debug.Printf("writeCipherBlock: wrote %d ciphertext bytes to block %d\n",
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written, blockNo)
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return err
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}
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// Perform RMW cycle on block
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// Write "data" into file location specified in "b"
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func (be *CryptFile) rmwWrite(b intraBlock, data []byte, f *os.File) error {
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if b.length != int64(len(data)) {
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panic("Length mismatch")
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}
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oldBlock, err := be.readCipherBlock(b.blockNo)
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if err != nil {
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return err
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}
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newBlockLen := b.offset + b.length
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debug.Printf("newBlockLen := %d + %d\n", b.offset, b.length)
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var newBlock []byte
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// Write goes beyond the old block and grows the file?
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// Must create a bigger newBlock
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if newBlockLen > int64(len(oldBlock)) {
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newBlock = make([]byte, newBlockLen)
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} else {
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newBlock = make([]byte, len(oldBlock))
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}
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// Fill with old data
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copy(newBlock, oldBlock)
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// Then overwrite the relevant parts with new data
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copy(newBlock[b.offset:b.offset + b.length], data)
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// Actual write
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err = be.writeCipherBlock(b.blockNo, newBlock)
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if err != nil {
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// An incomplete write to a ciphertext block means that the whole block
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// is destroyed.
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fmt.Printf("rmwWrite: Write error: %s\n", err)
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}
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return err
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}
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