fix(backups): improved archive encryption [EE-6764] (#11489)

api/crypto/nonce.go

@@ -0,0 +1,61 @@
+package crypto
+
+import (
+	"crypto/rand"
+	"errors"
+	"io"
+)
+
+type Nonce struct {
+	val []byte
+}
+
+func NewNonce(size int) *Nonce {
+	return &Nonce{val: make([]byte, size)}
+}
+
+// NewRandomNonce generates a new initial nonce with the lower byte set to a random value
+// This ensures there are plenty of nonce values availble before rolling over
+// Based on ideas from the Secure Programming Cookbook for C and C++ by John Viega, Matt Messier
+// https://www.oreilly.com/library/view/secure-programming-cookbook/0596003943/ch04s09.html
+func NewRandomNonce(size int) (*Nonce, error) {
+	randomBytes := 1
+	if size <= randomBytes {
+		return nil, errors.New("nonce size must be greater than the number of random bytes")
+	}
+
+	randomPart := make([]byte, randomBytes)
+	if _, err := rand.Read(randomPart); err != nil {
+		return nil, err
+	}
+
+	zeroPart := make([]byte, size-randomBytes)
+	nonceVal := append(randomPart, zeroPart...)
+	return &Nonce{val: nonceVal}, nil
+}
+
+func (n *Nonce) Read(stream io.Reader) error {
+	_, err := io.ReadFull(stream, n.val)
+	return err
+}
+
+func (n *Nonce) Value() []byte {
+	return n.val
+}
+
+func (n *Nonce) Increment() error {
+	// Start incrementing from the least significant byte
+	for i := len(n.val) - 1; i >= 0; i-- {
+		// Increment the current byte
+		n.val[i]++
+
+		// Check for overflow
+		if n.val[i] != 0 {
+			// No overflow, nonce is successfully incremented
+			return nil
+		}
+	}
+
+	// If we reach here, it means the nonce has overflowed
+	return errors.New("nonce overflow")
+}