Encryption async api (#17603)

* swarm/storage/encryption: async segmentwise encryption/decryption

* swarm/storage: adapt hasherstore to encryption API change

* swarm/api: adapt RefEncryption for AC to new Encryption API

* swarm/storage/encryption: address review comments

swarm/storage/encryption/encryption.go

@@ -21,6 +21,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"hash"
+	"sync"
 )
 
 const KeyLength = 32
@@ -28,84 +29,119 @@ const KeyLength = 32
 type Key []byte
 
 type Encryption interface {
-	Encrypt(data []byte, key Key) ([]byte, error)
-	Decrypt(data []byte, key Key) ([]byte, error)
+	Encrypt(data []byte) ([]byte, error)
+	Decrypt(data []byte) ([]byte, error)
 }
 
 type encryption struct {
-	padding  int
-	initCtr  uint32
-	hashFunc func() hash.Hash
+	key      Key              // the encryption key (hashSize bytes long)
+	keyLen   int              // length of the key = length of blockcipher block
+	padding  int              // encryption will pad the data upto this if > 0
+	initCtr  uint32           // initial counter used for counter mode blockcipher
+	hashFunc func() hash.Hash // hasher constructor function
 }
 
-func New(padding int, initCtr uint32, hashFunc func() hash.Hash) *encryption {
+// New constructs a new encryptor/decryptor
+func New(key Key, padding int, initCtr uint32, hashFunc func() hash.Hash) *encryption {
 	return &encryption{
+		key:      key,
+		keyLen:   len(key),
 		padding:  padding,
 		initCtr:  initCtr,
 		hashFunc: hashFunc,
 	}
 }
 
-func (e *encryption) Encrypt(data []byte, key Key) ([]byte, error) {
+// Encrypt encrypts the data and does padding if specified
+func (e *encryption) Encrypt(data []byte) ([]byte, error) {
 	length := len(data)
+	outLength := length
 	isFixedPadding := e.padding > 0
-	if isFixedPadding && length > e.padding {
-		return nil, fmt.Errorf("Data length longer than padding, data length %v padding %v", length, e.padding)
+	if isFixedPadding {
+		if length > e.padding {
+			return nil, fmt.Errorf("Data length longer than padding, data length %v padding %v", length, e.padding)
+		}
+		outLength = e.padding
 	}
-
-	paddedData := data
-	if isFixedPadding && length < e.padding {
-		paddedData = make([]byte, e.padding)
-		copy(paddedData[:length], data)
-		rand.Read(paddedData[length:])
-	}
-	return e.transform(paddedData, key), nil
+	out := make([]byte, outLength)
+	e.transform(data, out)
+	return out, nil
 }
 
-func (e *encryption) Decrypt(data []byte, key Key) ([]byte, error) {
+// Decrypt decrypts the data, if padding was used caller must know original length and truncate
+func (e *encryption) Decrypt(data []byte) ([]byte, error) {
 	length := len(data)
 	if e.padding > 0 && length != e.padding {
 		return nil, fmt.Errorf("Data length different than padding, data length %v padding %v", length, e.padding)
 	}
-
-	return e.transform(data, key), nil
+	out := make([]byte, length)
+	e.transform(data, out)
+	return out, nil
 }
 
-func (e *encryption) transform(data []byte, key Key) []byte {
-	dataLength := len(data)
-	transformedData := make([]byte, dataLength)
-	hasher := e.hashFunc()
-	ctr := e.initCtr
-	hashSize := hasher.Size()
-	for i := 0; i < dataLength; i += hashSize {
-		hasher.Write(key)
-
-		ctrBytes := make([]byte, 4)
-		binary.LittleEndian.PutUint32(ctrBytes, ctr)
-
-		hasher.Write(ctrBytes)
-
-		ctrHash := hasher.Sum(nil)
-		hasher.Reset()
-		hasher.Write(ctrHash)
-
-		segmentKey := hasher.Sum(nil)
-
-		hasher.Reset()
-
-		segmentSize := min(hashSize, dataLength-i)
-		for j := 0; j < segmentSize; j++ {
-			transformedData[i+j] = data[i+j] ^ segmentKey[j]
-		}
-		ctr++
+//
+func (e *encryption) transform(in, out []byte) {
+	inLength := len(in)
+	wg := sync.WaitGroup{}
+	wg.Add((inLength-1)/e.keyLen + 1)
+	for i := 0; i < inLength; i += e.keyLen {
+		l := min(e.keyLen, inLength-i)
+		// call transformations per segment (asyncronously)
+		go func(i int, x, y []byte) {
+			defer wg.Done()
+			e.Transcrypt(i, x, y)
+		}(i/e.keyLen, in[i:i+l], out[i:i+l])
 	}
-	return transformedData
+	// pad the rest if out is longer
+	pad(out[inLength:])
+	wg.Wait()
 }
 
-func GenerateRandomKey() (Key, error) {
-	key := make([]byte, KeyLength)
-	_, err := rand.Read(key)
-	return key, err
+// used for segmentwise transformation
+// if in is shorter than out, padding is used
+func (e *encryption) Transcrypt(i int, in []byte, out []byte) {
+	// first hash key with counter (initial counter + i)
+	hasher := e.hashFunc()
+	hasher.Write(e.key)
+
+	ctrBytes := make([]byte, 4)
+	binary.LittleEndian.PutUint32(ctrBytes, uint32(i)+e.initCtr)
+	hasher.Write(ctrBytes)
+
+	ctrHash := hasher.Sum(nil)
+	hasher.Reset()
+
+	// second round of hashing for selective disclosure
+	hasher.Write(ctrHash)
+	segmentKey := hasher.Sum(nil)
+	hasher.Reset()
+
+	// XOR bytes uptil length of in (out must be at least as long)
+	inLength := len(in)
+	for j := 0; j < inLength; j++ {
+		out[j] = in[j] ^ segmentKey[j]
+	}
+	// insert padding if out is longer
+	pad(out[inLength:])
+}
+
+func pad(b []byte) {
+	l := len(b)
+	for total := 0; total < l; {
+		read, _ := rand.Read(b[total:])
+		total += read
+	}
+}
+
+// GenerateRandomKey generates a random key of length l
+func GenerateRandomKey(l int) Key {
+	key := make([]byte, l)
+	var total int
+	for total < l {
+		read, _ := rand.Read(key[total:])
+		total += read
+	}
+	return key
 }
 
 func min(x, y int) int {