added fs encryption overlay

pkg/provider/crypto/helper.go

@@ -0,0 +1,78 @@
+package crypto
+
+import (
+	"cachefs/pkg/provider"
+	"crypto/rand"
+	"io"
+	"math"
+)
+
+func isZero(nonce []byte) bool {
+	for i := 0; i < len(nonce); i++ {
+		if nonce[i] != 0 {
+			return false
+		}
+	}
+	return true
+}
+
+func initNonce(f provider.File) (nonce []byte, err error) {
+	nonce = make([]byte, KDFNonceSize)
+	n, err := io.ReadFull(f, nonce)
+	if err != nil || n != len(nonce) || isZero(nonce) {
+		_, err = io.ReadFull(rand.Reader, nonce)
+		if err != nil {
+			return
+		}
+		_, err = f.Seek(0, io.SeekStart)
+		if err != nil {
+			return
+		}
+		_, err = f.Write(nonce)
+		return
+	}
+	return
+}
+
+func incNonce(nonce *[NonceSize]byte) {
+	for i := len(nonce) - 2; i >= 0; i-- {
+		nonce[i]++
+		if nonce[i] != 0 {
+			break
+		} else if i == 0 {
+			// The counter is 88 bits, this is unreachable.
+			panic("stream: chunk counter wrapped around")
+		}
+	}
+}
+
+func Size(s int64) int64 {
+	return KDFNonceSize + s + (int64(math.Ceil(float64(s)/ChunkSize)) * Overhead)
+}
+
+func RealSize(s int64) int64 {
+	s -= KDFNonceSize
+	return s - (((s / FullSize) + 1) * Overhead)
+}
+
+func chunkNum(o int64) int64 {
+	return int64(math.Ceil(float64(o) / ChunkSize))
+}
+
+func align(o int64) (cn, off, roff int64) {
+	cn = chunkNum(o)
+	off = cn * FullSize
+	roff = o - (cn * ChunkSize)
+	if roff < 0 {
+		cn--
+		off = cn * FullSize
+		roff = o - (cn * ChunkSize)
+	}
+	return
+}
+
+func inc(nonce *[NonceSize]byte, n int64) {
+	for i := int64(0); i < n; i++ {
+		incNonce(nonce)
+	}
+}