performance optimization for extract encrypted 7z

internal/aes7z/key.go

@@ -4,12 +4,50 @@ import (
 	"bytes"
 	"crypto/sha256"
 	"encoding/binary"
+	"sync"
 
 	"golang.org/x/text/encoding/unicode"
 	"golang.org/x/text/transform"
 )
 
+type keyCacheItem struct {
+	password string
+	cycles   int
+	salt     []byte
+	key      []byte
+}
+
+func (c *keyCacheItem) hittest(password string, cycles int, salt []byte) bool {
+	return c.password == password && c.cycles == cycles && bytes.Equal(salt, c.salt)
+}
+
+var keyCache []*keyCacheItem = []*keyCacheItem{}
+var keyCacheLock sync.RWMutex
+
+func findKeyCached(password string, cycles int, salt []byte) []byte {
+	keyCacheLock.RLock()
+	defer keyCacheLock.RUnlock()
+	for _, kci := range keyCache {
+		if kci.hittest(password, cycles, salt) {
+			return kci.key
+		}
+	}
+
+	return nil
+}
+
+func recordKeyCached(password string, cycles int, salt []byte, key []byte) {
+	keyCacheLock.Lock()
+	defer keyCacheLock.Unlock()
+	keyCache = append(keyCache, &keyCacheItem{password: password, cycles: cycles, salt: salt, key: key})
+}
+
 func calculateKey(password string, cycles int, salt []byte) []byte {
+	k := findKeyCached(password, cycles, salt)
+	if len(k) > 0 {
+		// key found in cache
+		return k
+	}
 	b := bytes.NewBuffer(salt)
 
 	// Convert password to UTF-16LE
@@ -30,5 +68,6 @@ func calculateKey(password string, cycles int, salt []byte) []byte {
 		copy(key, h.Sum(nil))
 	}
 
+	recordKeyCached(password, cycles, salt, key)
 	return key
 }