package contentenc // File content encryption / decryption import ( "bytes" "encoding/binary" "encoding/hex" "errors" "github.com/rfjakob/gocryptfs/internal/cryptocore" "github.com/rfjakob/gocryptfs/internal/tlog" ) const ( // Default plaintext block size DefaultBS = 4096 ) type ContentEnc struct { // Cryptographic primitives cryptoCore *cryptocore.CryptoCore // Plaintext block size plainBS uint64 // Ciphertext block size cipherBS uint64 // All-zero block of size cipherBS, for fast compares allZeroBlock []byte } func New(cc *cryptocore.CryptoCore, plainBS uint64) *ContentEnc { cipherBS := plainBS + uint64(cc.IVLen) + cryptocore.AuthTagLen return &ContentEnc{ cryptoCore: cc, plainBS: plainBS, cipherBS: cipherBS, allZeroBlock: make([]byte, cipherBS), } } func (be *ContentEnc) PlainBS() uint64 { return be.plainBS } // DecryptBlocks - Decrypt a number of blocks func (be *ContentEnc) 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, fileId) if err != nil { break } pBuf.Write(pBlock) firstBlockNo++ } return pBuf.Bytes(), err } // 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 passtrough. 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) { tlog.Debug.Printf("DecryptBlock: file hole encountered") return make([]byte, be.plainBS), nil } if len(ciphertext) < be.cryptoCore.IVLen { tlog.Warn.Printf("DecryptBlock: Block is too short: %d bytes", len(ciphertext)) return nil, errors.New("Block is too short") } // Extract nonce nonce := ciphertext[:be.cryptoCore.IVLen] ciphertextOrig := ciphertext ciphertext = ciphertext[be.cryptoCore.IVLen:] // Decrypt var plaintext []byte aData := make([]byte, 8) aData = append(aData, fileId...) binary.BigEndian.PutUint64(aData, blockNo) plaintext, err := be.cryptoCore.Gcm.Open(plaintext, nonce, ciphertext, aData) if err != nil { tlog.Warn.Printf("DecryptBlock: %s, len=%d", err.Error(), len(ciphertextOrig)) tlog.Debug.Println(hex.Dump(ciphertextOrig)) return nil, err } return plaintext, nil } // encryptBlock - Encrypt and add IV and MAC func (be *ContentEnc) EncryptBlock(plaintext []byte, blockNo uint64, fileID []byte) []byte { // Empty block? if len(plaintext) == 0 { return plaintext } // Get fresh nonce nonce := be.cryptoCore.GcmIVGen.Get() // Authenticate block with block number and file ID aData := make([]byte, 8) binary.BigEndian.PutUint64(aData, blockNo) aData = append(aData, fileID...) // Encrypt plaintext and append to nonce ciphertext := be.cryptoCore.Gcm.Seal(nonce, nonce, plaintext, aData) 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 { // 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] }