feat(ximalaya): initial support

algo/ximalaya/x3m_crypto.go

@@ -0,0 +1,40 @@
+package ximalaya
+
+import (
+	_ "embed"
+	"encoding/binary"
+)
+
+var x3mKey = [...]byte{
+	'3', '9', '8', '9', 'd', '1', '1', '1',
+	'a', 'a', 'd', '5', '6', '1', '3', '9',
+	'4', '0', 'f', '4', 'f', 'c', '4', '4',
+	'b', '6', '3', '9', 'b', '2', '9', '2',
+}
+
+const x3mHeaderSize = 1024
+
+var x3mScrambleTable = [x3mHeaderSize]uint16{}
+
+//go:embed x3m_scramble_table.bin
+var x3mScrambleTableBytes []byte
+
+func init() {
+	if len(x3mScrambleTableBytes) != 2*x3mHeaderSize {
+		panic("invalid x3m scramble table")
+	}
+	for i := range x3mScrambleTable {
+		x3mScrambleTable[i] = binary.LittleEndian.Uint16(x3mScrambleTableBytes[i*2:])
+	}
+}
+
+// decryptX3MHeader decrypts the header of ximalaya .x3m file.
+// make sure input src is 1024 (x3mHeaderSize) bytes long.
+func decryptX3MHeader(src []byte) []byte {
+	dst := make([]byte, len(src))
+	for dstIdx := range src {
+		srcIdx := x3mScrambleTable[dstIdx]
+		dst[dstIdx] = src[srcIdx] ^ x3mKey[dstIdx%len(x3mKey)]
+	}
+	return dst
+}