feat: 新增XTS/CCM流式与KDF能力，补充安全测试并更新README/CHANGELOG

encodingx/encoding.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"io"
 	"os"
+	"strings"
 )
 
 var (
@@ -192,12 +193,12 @@ func Base85Encode(bstr []byte) string {
 }
 
 func Base85Decode(str string) ([]byte, error) {
-	out := make([]byte, len(str))
-	n, _, err := ascii85.Decode(out, []byte(str), true)
+	dec := ascii85.NewDecoder(strings.NewReader(str))
+	out, err := io.ReadAll(dec)
 	if err != nil {
 		return nil, err
 	}
-	return out[:n], nil
+	return out, nil
 }
 
 func Base85EncodeFile(src, dst string, progress func(float64)) error {

encodingx/encoding_test.go

@@ -96,3 +96,36 @@ func TestBase64AndBase85FileRoundTrip(t *testing.T) {
 		t.Fatalf("base85 file roundtrip mismatch")
 	}
 }
+
+func TestBase85RoundTripEdgeLengths(t *testing.T) {
+	for n := 0; n <= 128; n++ {
+		plain := make([]byte, n)
+		for i := range plain {
+			plain[i] = byte((i*37 + n) % 256)
+		}
+
+		e := Base85Encode(plain)
+		d, err := Base85Decode(e)
+		if err != nil {
+			t.Fatalf("Base85Decode failed at len=%d: %v", n, err)
+		}
+		if !bytes.Equal(d, plain) {
+			t.Fatalf("base85 mismatch at len=%d", n)
+		}
+	}
+}
+
+func TestBase91RoundTripEdgeLengths(t *testing.T) {
+	for n := 0; n <= 256; n++ {
+		plain := make([]byte, n)
+		for i := range plain {
+			plain[i] = byte((i*53 + n) % 256)
+		}
+
+		e := Base91Encode(plain)
+		d := Base91Decode(e)
+		if !bytes.Equal(d, plain) {
+			t.Fatalf("base91 mismatch at len=%d", n)
+		}
+	}
+}