Implement Erasure Coding

duplicacy/duplicacy_main.go

@@ -458,8 +458,26 @@ func configRepository(context *cli.Context, init bool) {
 		if iterations == 0 {
 			iterations = duplicacy.CONFIG_DEFAULT_ITERATIONS
 		}
+
+		dataShards := 0
+		parityShards := 0
+		shards := context.String("erasure-coding")
+		if shards != "" {
+			shardsRegex := regexp.MustCompile(`^([0-9]+):([0-9]+)$`)
+			matched := shardsRegex.FindStringSubmatch(shards)
+			if matched == nil {
+				duplicacy.LOG_ERROR("STORAGE_ERASURECODE", "Invalid erasure coding parameters: %s", shards)
+			} else {
+				dataShards, _ = strconv.Atoi(matched[1])
+				parityShards, _ = strconv.Atoi(matched[2])
+				if dataShards == 0 || dataShards > 256 || parityShards == 0 || parityShards > dataShards {
+					duplicacy.LOG_ERROR("STORAGE_ERASURECODE", "Invalid erasure coding parameters: %s", shards)
+				}
+			}
+		}
+
 		duplicacy.ConfigStorage(storage, iterations, compressionLevel, averageChunkSize, maximumChunkSize,
-			minimumChunkSize, storagePassword, otherConfig, bitCopy, context.String("key"))
+			minimumChunkSize, storagePassword, otherConfig, bitCopy, context.String("key"), dataShards, parityShards)
 	}
 
 	duplicacy.Preferences = append(duplicacy.Preferences, preference)
@@ -1403,6 +1421,11 @@ func main() {
 					Usage:    "the RSA public key to encrypt file chunks",
 					Argument: "<public key>",
 				},
+				cli.StringFlag{
+					Name:     "erasure-coding",
+					Usage:    "enable erasure coding to protect against storage corruption",
+					Argument: "<data shards>:<parity shards>",
+				},
 			},
 			Usage:     "Initialize the storage if necessary and the current directory as the repository",
 			ArgsUsage: "<snapshot id> <storage url>",
@@ -1882,6 +1905,11 @@ func main() {
 					Usage:    "the RSA public key to encrypt file chunks",
 					Argument: "<public key>",
 				},
+				cli.StringFlag{
+					Name:     "erasure-coding",
+					Usage:    "enable erasure coding to protect against storage corruption",
+					Argument: "<data shards>:<parity shards>",
+				},
 			},
 			Usage:     "Add an additional storage to be used for the existing repository",
 			ArgsUsage: "<storage name> <snapshot id> <storage url>",

src/duplicacy_backupmanager_test.go

@@ -226,12 +226,20 @@ func TestBackupManager(t *testing.T) {
 	cleanStorage(storage)
 
 	time.Sleep(time.Duration(delay) * time.Second)
+
+	dataShards := 0
+	parityShards := 0
+	if testErasureCoding {
+		dataShards = 5
+		parityShards = 2
+	}
+
 	if testFixedChunkSize {
-		if !ConfigStorage(storage, 16384, 100, 64*1024, 64*1024, 64*1024, password, nil, false, "") {
+		if !ConfigStorage(storage, 16384, 100, 64*1024, 64*1024, 64*1024, password, nil, false, "", dataShards, parityShards) {
 			t.Errorf("Failed to initialize the storage")
 		}
 	} else {
-		if !ConfigStorage(storage, 16384, 100, 64*1024, 256*1024, 16*1024, password, nil, false, "") {
+		if !ConfigStorage(storage, 16384, 100, 64*1024, 256*1024, 16*1024, password, nil, false, "", dataShards, parityShards) {
 			t.Errorf("Failed to initialize the storage")
 		}
 	}

src/duplicacy_chunk.go

@@ -22,6 +22,8 @@ import (
 	"runtime"
 
 	"github.com/bkaradzic/go-lz4"
+	"github.com/minio/highwayhash"
+	"github.com/klauspost/reedsolomon"
 )
 
 // A chunk needs to acquire a new buffer and return the old one for every encrypt/decrypt operation, therefore
@@ -68,11 +70,13 @@ type Chunk struct {
 }
 
 // Magic word to identify a duplicacy format encrypted file, plus a version number.
-var ENCRYPTION_HEADER = "duplicacy\000"
+var ENCRYPTION_BANNER = "duplicacy\000"
 
 // RSA encrypted chunks start with "duplicacy\002"
 var ENCRYPTION_VERSION_RSA byte = 2
 
+var ERASURE_CODING_BANNER = "duplicacy\003"
+
 // CreateChunk creates a new chunk.
 func CreateChunk(config *Config, bufferNeeded bool) *Chunk {
 
@@ -224,7 +228,7 @@ func (chunk *Chunk) Encrypt(encryptionKey []byte, derivationKey string, isSnapsh
 		// Start with the magic number and the version number.
 		if usingRSA {
 			// RSA encryption starts "duplicacy\002"
-			encryptedBuffer.Write([]byte(ENCRYPTION_HEADER)[:len(ENCRYPTION_HEADER) - 1])
+			encryptedBuffer.Write([]byte(ENCRYPTION_BANNER)[:len(ENCRYPTION_BANNER) - 1])
 			encryptedBuffer.Write([]byte{ENCRYPTION_VERSION_RSA})
 
 			// Then the encrypted key
@@ -235,7 +239,7 @@ func (chunk *Chunk) Encrypt(encryptionKey []byte, derivationKey string, isSnapsh
 			binary.Write(encryptedBuffer, binary.LittleEndian, uint16(len(encryptedKey)))
 			encryptedBuffer.Write(encryptedKey)
 		} else {
-			encryptedBuffer.Write([]byte(ENCRYPTION_HEADER))
+			encryptedBuffer.Write([]byte(ENCRYPTION_BANNER))
 		}
 
 		// Followed by the nonce
@@ -248,7 +252,7 @@ func (chunk *Chunk) Encrypt(encryptionKey []byte, derivationKey string, isSnapsh
 		offset = encryptedBuffer.Len()
 	}
 
-	// offset is either 0 or the length of header + nonce
+	// offset is either 0 or the length of banner + nonce
 
 	if chunk.config.CompressionLevel >= -1 && chunk.config.CompressionLevel <= 9 {
 		deflater, _ := zlib.NewWriterLevel(encryptedBuffer, chunk.config.CompressionLevel)
@@ -273,26 +277,79 @@ func (chunk *Chunk) Encrypt(encryptionKey []byte, derivationKey string, isSnapsh
 		return fmt.Errorf("Invalid compression level: %d", chunk.config.CompressionLevel)
 	}
 
-	if len(encryptionKey) == 0 {
-		chunk.buffer, encryptedBuffer = encryptedBuffer, chunk.buffer
-		return nil
+	if len(encryptionKey) > 0 {
+
+		// PKCS7 is used.  The sizes of compressed chunks leak information about the original chunks so we want the padding sizes
+		// to be the maximum allowed by PKCS7
+		dataLength := encryptedBuffer.Len() - offset
+		paddingLength := 256 - dataLength%256
+
+		encryptedBuffer.Write(bytes.Repeat([]byte{byte(paddingLength)}, paddingLength))
+		encryptedBuffer.Write(bytes.Repeat([]byte{0}, gcm.Overhead()))
+
+		// The encrypted data will be appended to the duplicacy banner and the once.
+		encryptedBytes := gcm.Seal(encryptedBuffer.Bytes()[:offset], nonce,
+			encryptedBuffer.Bytes()[offset:offset+dataLength+paddingLength], nil)
+
+		encryptedBuffer.Truncate(len(encryptedBytes))
 	}
 
-	// PKCS7 is used.  Compressed chunk sizes leaks information about the original chunks so we want the padding sizes
-	// to be the maximum allowed by PKCS7
-	dataLength := encryptedBuffer.Len() - offset
-	paddingLength := 256 - dataLength%256
+	if chunk.config.DataShards == 0 || chunk.config.ParityShards == 0 {
+		chunk.buffer, encryptedBuffer = encryptedBuffer, chunk.buffer
+		return
+	}
 
-	encryptedBuffer.Write(bytes.Repeat([]byte{byte(paddingLength)}, paddingLength))
-	encryptedBuffer.Write(bytes.Repeat([]byte{0}, gcm.Overhead()))
+	// Start erasure coding
+	encoder, err := reedsolomon.New(chunk.config.DataShards, chunk.config.ParityShards)
+	if err != nil {
+		return err
+	}
+	chunkSize := len(encryptedBuffer.Bytes())
+	shardSize := (chunkSize + chunk.config.DataShards - 1) / chunk.config.DataShards
+	// Append zeros to make the last shard to have the same size as other
+	encryptedBuffer.Write(make([]byte, shardSize * chunk.config.DataShards - chunkSize))
+	// Grow the buffer for parity shards
+	encryptedBuffer.Grow(shardSize * chunk.config.ParityShards)
+	// Now create one slice for each shard, reusing the data in the buffer
+	data := make([][]byte, chunk.config.DataShards + chunk.config.ParityShards)
+	for i := 0; i < chunk.config.DataShards + chunk.config.ParityShards; i++ {
+		data[i] = encryptedBuffer.Bytes()[i * shardSize: (i + 1) * shardSize]
+	}
+	// This populates the parity shard
+	encoder.Encode(data)
 
-	// The encrypted data will be appended to the duplicacy header and the once.
-	encryptedBytes := gcm.Seal(encryptedBuffer.Bytes()[:offset], nonce,
-		encryptedBuffer.Bytes()[offset:offset+dataLength+paddingLength], nil)
+	// Prepare the chunk to be uploaded
+	chunk.buffer.Reset()
+	// First the banner
+	chunk.buffer.Write([]byte(ERASURE_CODING_BANNER))
+	// Then the header which includes the chunk size, data/parity and a 2-byte checksum
+	header := make([]byte, 14)
+	binary.LittleEndian.PutUint64(header[0:], uint64(chunkSize))
+	binary.LittleEndian.PutUint16(header[8:], uint16(chunk.config.DataShards))
+	binary.LittleEndian.PutUint16(header[10:], uint16(chunk.config.ParityShards))
+	header[12] = header[0] ^ header[2] ^ header[4] ^ header[6] ^ header[8] ^ header[10]
+	header[13] = header[1] ^ header[3] ^ header[5] ^ header[7] ^ header[9] ^ header[11]
+	chunk.buffer.Write(header)
+	// Calculate the highway hash for each shard
+	hashKey := make([]byte, 32)
+	for _, part := range data {
+		hasher, err := highwayhash.New(hashKey)
+		if err != nil {
+			return err
+		}
+		_, err = hasher.Write(part)
+		if err != nil {
+			return err
+		}
+		chunk.buffer.Write(hasher.Sum(nil))
+	}
 
-	encryptedBuffer.Truncate(len(encryptedBytes))
-
-	chunk.buffer, encryptedBuffer = encryptedBuffer, chunk.buffer
+	// Copy the data
+	for _, part := range data {
+		chunk.buffer.Write(part)
+	}
+	// Append the header again for redundancy
+	chunk.buffer.Write(header)
 
 	return nil
 
@@ -322,7 +379,122 @@ func (chunk *Chunk) Decrypt(encryptionKey []byte, derivationKey string) (err err
 	}()
 
 	chunk.buffer, encryptedBuffer = encryptedBuffer, chunk.buffer
-	headerLength := len(ENCRYPTION_HEADER)
+	bannerLength := len(ENCRYPTION_BANNER)
+
+	if len(encryptedBuffer.Bytes()) > bannerLength && string(encryptedBuffer.Bytes()[:bannerLength]) == ERASURE_CODING_BANNER {
+
+		// The chunk was encoded with erasure coding
+		if len(encryptedBuffer.Bytes()) < bannerLength + 14 {
+			return fmt.Errorf("Erasure coding header truncated (%d bytes)", len(encryptedBuffer.Bytes()))
+		}
+		// Check the header checksum
+		header := encryptedBuffer.Bytes()[bannerLength: bannerLength + 14]
+		if header[12] != header[0] ^ header[2] ^ header[4] ^ header[6] ^ header[8] ^ header[10] ||
+		   header[13] != header[1] ^ header[3] ^ header[5] ^ header[7] ^ header[9] ^ header[11] {
+			return fmt.Errorf("Erasure coding header corrupted (%x)", header)
+		}
+
+		// Read the parameters
+		chunkSize := int(binary.LittleEndian.Uint64(header[0:8]))
+		dataShards := int(binary.LittleEndian.Uint16(header[8:10]))
+		parityShards := int(binary.LittleEndian.Uint16(header[10:12]))
+		shardSize := (chunkSize + chunk.config.DataShards - 1) / chunk.config.DataShards
+		// This is the length the chunk file should have
+		expectedLength := bannerLength + 2 * len(header) + (dataShards + parityShards) * (shardSize + 32)
+		// The minimum length that can be recovered from
+		minimumLength := bannerLength + len(header) + (dataShards + parityShards) * 32 + dataShards * shardSize
+		LOG_DEBUG("CHUNK_ERASURECODE", "Chunk size: %d bytes, data size: %d, parity: %d/%d", chunkSize, len(encryptedBuffer.Bytes()), dataShards, parityShards)
+		if len(encryptedBuffer.Bytes()) > expectedLength {
+			LOG_WARN("CHUNK_ERASURECODE", "Chunk has %d bytes (instead of %d)", len(encryptedBuffer.Bytes()), expectedLength)
+		} else if len(encryptedBuffer.Bytes()) == expectedLength {
+			// Correct size; fall through
+		} else if len(encryptedBuffer.Bytes()) > minimumLength {
+			LOG_WARN("CHUNK_ERASURECODE", "Chunk is truncated (%d out of %d bytes)", len(encryptedBuffer.Bytes()), expectedLength)
+		} else {
+			return fmt.Errorf("Not enough chunk data for recovery; chunk size: %d bytes, data size: %d, parity: %d/%d", chunkSize, len(encryptedBuffer.Bytes()), dataShards, parityShards)
+		}
+
+		// Where the hashes start
+		hashOffset := bannerLength + len(header)
+		// Where the data start
+		dataOffset := hashOffset + (dataShards + parityShards) * 32
+
+		data := make([][]byte, dataShards + parityShards)
+		recoveryNeeded := false
+		hashKey := make([]byte, 32)
+		availableShards := 0
+		for i := 0; i < dataShards + parityShards; i++ {
+			start := dataOffset + i * shardSize
+			if start + shardSize > len(encryptedBuffer.Bytes()) {
+				// the current shard is incomplete
+				break
+			}
+			// Now verify the hash
+			hasher, err := highwayhash.New(hashKey)
+			if err != nil {
+				return err
+			}
+			_, err = hasher.Write(encryptedBuffer.Bytes()[start: start + shardSize])
+			if err != nil {
+				return err
+			}
+			if bytes.Compare(hasher.Sum(nil), encryptedBuffer.Bytes()[hashOffset + i * 32: hashOffset + (i + 1) * 32]) != 0 {
+				if i < dataShards {
+					recoveryNeeded = true
+				}
+			} else {
+				// The shard is good
+				data[i] = encryptedBuffer.Bytes()[start: start + shardSize]
+				availableShards++
+				if availableShards >= dataShards {
+					// We have enough shards to recover; skip the remaining shards
+					break
+				}
+			}
+		}
+
+		if !recoveryNeeded {
+			// Remove the padding zeros from the last shard
+			encryptedBuffer.Truncate(dataOffset + chunkSize)
+			// Skip the header and hashes
+			encryptedBuffer.Read(encryptedBuffer.Bytes()[:dataOffset])
+		} else {
+			if availableShards < dataShards {
+				return fmt.Errorf("Not enough chunk data for recover; only %d out of %d shards are complete", availableShards, dataShards + parityShards)
+			}
+
+			// Show the validity of shards using a string of * and -
+			slots := ""
+			for _, part := range data {
+				if len(part) != 0 {
+					slots += "*"
+				} else {
+					slots += "-"
+				}
+			}
+
+			LOG_WARN("CHUNK_ERASURECODE", "Recovering a %d byte chunk from %d byte shards: %s", chunkSize, shardSize, slots)
+			encoder, err := reedsolomon.New(dataShards, parityShards)
+			if err != nil {
+				return err
+			}
+			err = encoder.Reconstruct(data)
+			if err != nil {
+				return err
+			}
+			LOG_DEBUG("CHUNK_ERASURECODE", "Chunk data successfully recovered")
+			buffer := AllocateChunkBuffer()
+			buffer.Reset()
+			for i := 0; i < dataShards; i++ {
+				buffer.Write(data[i])
+			}
+			buffer.Truncate(chunkSize)
+
+			ReleaseChunkBuffer(encryptedBuffer)
+			encryptedBuffer = buffer
+		}
+
+	}
 
 	if len(encryptionKey) > 0 {
 
@@ -340,15 +512,15 @@ func (chunk *Chunk) Decrypt(encryptionKey []byte, derivationKey string) (err err
 			key = hasher.Sum(nil)
 		}
 
-		if len(encryptedBuffer.Bytes()) < headerLength + 12 {
+		if len(encryptedBuffer.Bytes()) < bannerLength + 12 {
 			return fmt.Errorf("No enough encrypted data (%d bytes) provided", len(encryptedBuffer.Bytes()))
 		}
 
-		if string(encryptedBuffer.Bytes()[:headerLength-1]) != ENCRYPTION_HEADER[:headerLength-1] {
+		if string(encryptedBuffer.Bytes()[:bannerLength-1]) != ENCRYPTION_BANNER[:bannerLength-1] {
 			return fmt.Errorf("The storage doesn't seem to be encrypted")
 		}
 
-		encryptionVersion := encryptedBuffer.Bytes()[headerLength-1]
+		encryptionVersion := encryptedBuffer.Bytes()[bannerLength-1]
 		if encryptionVersion != 0 && encryptionVersion != ENCRYPTION_VERSION_RSA {
 			return fmt.Errorf("Unsupported encryption version %d", encryptionVersion)
 		}
@@ -359,14 +531,14 @@ func (chunk *Chunk) Decrypt(encryptionKey []byte, derivationKey string) (err err
 				return fmt.Errorf("An RSA private key is required to decrypt the chunk")
 			}
 
-			encryptedKeyLength := binary.LittleEndian.Uint16(encryptedBuffer.Bytes()[headerLength:headerLength+2])
+			encryptedKeyLength := binary.LittleEndian.Uint16(encryptedBuffer.Bytes()[bannerLength:bannerLength+2])
 
-			if len(encryptedBuffer.Bytes()) < headerLength + 14 + int(encryptedKeyLength) {
+			if len(encryptedBuffer.Bytes()) < bannerLength + 14 + int(encryptedKeyLength) {
 				return fmt.Errorf("No enough encrypted data (%d bytes) provided", len(encryptedBuffer.Bytes()))
 			}
 
-			encryptedKey := encryptedBuffer.Bytes()[headerLength + 2:headerLength + 2 + int(encryptedKeyLength)]
-			headerLength += 2 + int(encryptedKeyLength)
+			encryptedKey := encryptedBuffer.Bytes()[bannerLength + 2:bannerLength + 2 + int(encryptedKeyLength)]
+			bannerLength += 2 + int(encryptedKeyLength)
 
 			decryptedKey, err := rsa.DecryptOAEP(sha256.New(), rand.Reader, chunk.config.rsaPrivateKey, encryptedKey, nil)
 			if err != nil {
@@ -385,8 +557,8 @@ func (chunk *Chunk) Decrypt(encryptionKey []byte, derivationKey string) (err err
 			return err
 		}
 
-		offset = headerLength + gcm.NonceSize()
-		nonce := encryptedBuffer.Bytes()[headerLength:offset]
+		offset = bannerLength + gcm.NonceSize()
+		nonce := encryptedBuffer.Bytes()[bannerLength:offset]
 
 		decryptedBytes, err := gcm.Open(encryptedBuffer.Bytes()[:offset], nonce,
 			encryptedBuffer.Bytes()[offset:], nil)

src/duplicacy_chunk_test.go

@@ -12,7 +12,46 @@ import (
 	"testing"
 )
 
-func TestChunk(t *testing.T) {
+func TestErasureCoding(t *testing.T) {
+	key := []byte("duplicacydefault")
+
+	config := CreateConfig()
+	config.HashKey = key
+	config.IDKey = key
+	config.MinimumChunkSize = 100
+	config.CompressionLevel = DEFAULT_COMPRESSION_LEVEL
+	config.DataShards = 5
+    config.ParityShards = 2
+
+	chunk := CreateChunk(config, true)
+	chunk.Reset(true)
+	data := make([]byte, 100)
+	for i := 0; i < len(data); i++ {
+		data[i] = byte(i)
+	}
+	chunk.Write(data)
+	err := chunk.Encrypt([]byte(""), "", false)
+	if err != nil {
+		t.Errorf("Failed to encrypt the test data: %v", err)
+		return
+	}
+
+	encryptedData := make([]byte, chunk.GetLength())
+	copy(encryptedData, chunk.GetBytes())
+
+	crypto_rand.Read(encryptedData[280:300])
+
+	chunk.Reset(false)
+	chunk.Write(encryptedData)
+	err = chunk.Decrypt([]byte(""), "")
+	if err != nil {
+		t.Errorf("Failed to decrypt the data: %v", err)
+		return
+	}
+	return
+}
+
+func TestChunkBasic(t *testing.T) {
 
 	key := []byte("duplicacydefault")
 
@@ -32,7 +71,10 @@ func TestChunk(t *testing.T) {
 		config.rsaPublicKey = privateKey.Public().(*rsa.PublicKey)
 	}
 
-	remainderLength := -1
+	if testErasureCoding {
+		config.DataShards = 5
+		config.ParityShards = 2
+	}
 
 	for i := 0; i < 500; i++ {
 
@@ -56,10 +98,14 @@ func TestChunk(t *testing.T) {
 		encryptedData := make([]byte, chunk.GetLength())
 		copy(encryptedData, chunk.GetBytes())
 
-		if remainderLength == -1 {
-			remainderLength = len(encryptedData) % 256
-		} else if len(encryptedData)%256 != remainderLength {
-			t.Errorf("Incorrect padding size")
+		if testErasureCoding {
+			offset := 24 + 32 * 7
+			start := rand.Int() % (len(encryptedData) - offset) + offset
+			length := (len(encryptedData) - offset) / 7
+			if start + length > len(encryptedData) {
+				length = len(encryptedData) - start
+			}
+			crypto_rand.Read(encryptedData[start: start+length])
 		}
 
 		chunk.Reset(false)

src/duplicacy_config.go

@@ -34,8 +34,8 @@ var DEFAULT_KEY = []byte("duplicacy")
 // standard zlib levels of -1 to 9.
 var DEFAULT_COMPRESSION_LEVEL = 100
 
-// The new header of the config file (to differentiate from the old format where the salt and iterations are fixed)
-var CONFIG_HEADER = "duplicacy\001"
+// The new banner of the config file (to differentiate from the old format where the salt and iterations are fixed)
+var CONFIG_BANNER = "duplicacy\001"
 
 // The length of the salt used in the new format
 var CONFIG_SALT_LENGTH = 32
@@ -70,6 +70,10 @@ type Config struct {
 	// for encrypting a non-chunk file
 	FileKey []byte `json:"-"`
 
+	// for erasure coding
+	DataShards int `json:'data-shards'`
+	ParityShards int `json:'parity-shards'`
+
 	// for RSA encryption
 	rsaPrivateKey *rsa.PrivateKey
 	rsaPublicKey *rsa.PublicKey
@@ -180,6 +184,10 @@ func (config *Config) Print() {
 		LOG_TRACE("CONFIG_INFO", "Metadata chunks are encrypted")
 	}
 
+	if config.DataShards != 0 && config.ParityShards != 0 {
+		LOG_TRACE("CONFIG_INFO", "Data shards: %d, parity shards: %d", config.DataShards, config.ParityShards)
+	}
+
 	if config.rsaPublicKey != nil {
 		pkisPublicKey, _ := x509.MarshalPKIXPublicKey(config.rsaPublicKey)
 
@@ -386,11 +394,11 @@ func DownloadConfig(storage Storage, password string) (config *Config, isEncrypt
 		return nil, false, err
 	}
 
-	if len(configFile.GetBytes()) < len(ENCRYPTION_HEADER) {
+	if len(configFile.GetBytes()) < len(ENCRYPTION_BANNER) {
 		return nil, false, fmt.Errorf("The storage has an invalid config file")
 	}
 
-	if string(configFile.GetBytes()[:len(ENCRYPTION_HEADER)-1]) == ENCRYPTION_HEADER[:len(ENCRYPTION_HEADER)-1] && len(password) == 0 {
+	if string(configFile.GetBytes()[:len(ENCRYPTION_BANNER)-1]) == ENCRYPTION_BANNER[:len(ENCRYPTION_BANNER)-1] && len(password) == 0 {
 		return nil, true, fmt.Errorf("The storage is likely to have been initialized with a password before")
 	}
 
@@ -398,23 +406,23 @@ func DownloadConfig(storage Storage, password string) (config *Config, isEncrypt
 
 	if len(password) > 0 {
 
-		if string(configFile.GetBytes()[:len(ENCRYPTION_HEADER)]) == ENCRYPTION_HEADER {
+		if string(configFile.GetBytes()[:len(ENCRYPTION_BANNER)]) == ENCRYPTION_BANNER {
 			// This is the old config format with a static salt and a fixed number of iterations
 			masterKey = GenerateKeyFromPassword(password, DEFAULT_KEY, CONFIG_DEFAULT_ITERATIONS)
 			LOG_TRACE("CONFIG_FORMAT", "Using a static salt and %d iterations for key derivation", CONFIG_DEFAULT_ITERATIONS)
-		} else if string(configFile.GetBytes()[:len(CONFIG_HEADER)]) == CONFIG_HEADER {
+		} else if string(configFile.GetBytes()[:len(CONFIG_BANNER)]) == CONFIG_BANNER {
 			// This is the new config format with a random salt and a configurable number of iterations
 			encryptedLength := len(configFile.GetBytes()) - CONFIG_SALT_LENGTH - 4
 
 			// Extract the salt and the number of iterations
-			saltStart := configFile.GetBytes()[len(CONFIG_HEADER):]
+			saltStart := configFile.GetBytes()[len(CONFIG_BANNER):]
 			iterations := binary.LittleEndian.Uint32(saltStart[CONFIG_SALT_LENGTH : CONFIG_SALT_LENGTH+4])
 			LOG_TRACE("CONFIG_ITERATIONS", "Using %d iterations for key derivation", iterations)
 			masterKey = GenerateKeyFromPassword(password, saltStart[:CONFIG_SALT_LENGTH], int(iterations))
 
-			// Copy to a temporary buffer to replace the header and remove the salt and the number of riterations
+			// Copy to a temporary buffer to replace the banner and remove the salt and the number of riterations
 			var encrypted bytes.Buffer
-			encrypted.Write([]byte(ENCRYPTION_HEADER))
+			encrypted.Write([]byte(ENCRYPTION_BANNER))
 			encrypted.Write(saltStart[CONFIG_SALT_LENGTH+4:])
 
 			configFile.Reset(false)
@@ -423,7 +431,7 @@ func DownloadConfig(storage Storage, password string) (config *Config, isEncrypt
 				LOG_ERROR("CONFIG_DOWNLOAD", "Encrypted config has %d bytes instead of expected %d bytes", len(configFile.GetBytes()), encryptedLength)
 			}
 		} else {
-			return nil, true, fmt.Errorf("The config file has an invalid header")
+			return nil, true, fmt.Errorf("The config file has an invalid banner")
 		}
 
 		// Decrypt the config file.  masterKey == nil means no encryption.
@@ -487,15 +495,15 @@ func UploadConfig(storage Storage, config *Config, password string, iterations i
 			return false
 		}
 
-		// The new encrypted format for config is CONFIG_HEADER + salt + #iterations + encrypted content
+		// The new encrypted format for config is CONFIG_BANNER + salt + #iterations + encrypted content
 		encryptedLength := len(chunk.GetBytes()) + CONFIG_SALT_LENGTH + 4
 
-		// Copy to a temporary buffer to replace the header and add the salt and the number of iterations
+		// Copy to a temporary buffer to replace the banner and add the salt and the number of iterations
 		var encrypted bytes.Buffer
-		encrypted.Write([]byte(CONFIG_HEADER))
+		encrypted.Write([]byte(CONFIG_BANNER))
 		encrypted.Write(salt)
 		binary.Write(&encrypted, binary.LittleEndian, uint32(iterations))
-		encrypted.Write(chunk.GetBytes()[len(ENCRYPTION_HEADER):])
+		encrypted.Write(chunk.GetBytes()[len(ENCRYPTION_BANNER):])
 
 		chunk.Reset(false)
 		chunk.Write(encrypted.Bytes())
@@ -528,7 +536,7 @@ func UploadConfig(storage Storage, config *Config, password string, iterations i
 // it simply creates a file named 'config' that stores various parameters as well as a set of keys if encryption
 // is enabled.
 func ConfigStorage(storage Storage, iterations int, compressionLevel int, averageChunkSize int, maximumChunkSize int,
-	minimumChunkSize int, password string, copyFrom *Config, bitCopy bool, keyFile string) bool {
+	minimumChunkSize int, password string, copyFrom *Config, bitCopy bool, keyFile string, dataShards int, parityShards int) bool {
 
 	exist, _, _, err := storage.GetFileInfo(0, "config")
 	if err != nil {
@@ -550,6 +558,10 @@ func ConfigStorage(storage Storage, iterations int, compressionLevel int, averag
 	if keyFile != "" {
 		config.loadRSAPublicKey(keyFile)
 	}
+
+	config.DataShards = dataShards
+	config.ParityShards = parityShards
+
 	return UploadConfig(storage, config, password, iterations)
 }
 

src/duplicacy_storage_test.go

@@ -28,6 +28,7 @@ var testQuickMode bool
 var testThreads int
 var testFixedChunkSize bool
 var testRSAEncryption bool
+var testErasureCoding bool
 
 func init() {
 	flag.StringVar(&testStorageName, "storage", "", "the test storage to use")
@@ -36,6 +37,7 @@ func init() {
 	flag.IntVar(&testThreads, "threads", 1, "number of downloading/uploading threads")
 	flag.BoolVar(&testFixedChunkSize, "fixed-chunk-size", false, "fixed chunk size")
 	flag.BoolVar(&testRSAEncryption, "rsa", false, "enable RSA encryption")
+	flag.BoolVar(&testErasureCoding, "erasure-coding", false, "enable Erasure Coding")
 	flag.Parse()
 }