Add vendor (steam)

vendor/github.com/Philipp15b/go-steam/cryptoutil/pkcs7.go

@@ -0,0 +1,25 @@
+package cryptoutil
+
+import (
+	"crypto/aes"
+)
+
+// Returns a new byte array padded with PKCS7 and prepended
+// with empty space of the AES block size (16 bytes) for the IV.
+func padPKCS7WithIV(src []byte) []byte {
+	missing := aes.BlockSize - (len(src) % aes.BlockSize)
+	newSize := len(src) + aes.BlockSize + missing
+	dest := make([]byte, newSize, newSize)
+	copy(dest[aes.BlockSize:], src)
+
+	padding := byte(missing)
+	for i := newSize - missing; i < newSize; i++ {
+		dest[i] = padding
+	}
+	return dest
+}
+
+func unpadPKCS7(src []byte) []byte {
+	padLen := src[len(src)-1]
+	return src[:len(src)-int(padLen)]
+}