Add vendor (steam)

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

@@ -0,0 +1,38 @@
+package cryptoutil
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+)
+
+// Performs an encryption using AES/CBC/PKCS7
+// with a random IV prepended using AES/ECB/None.
+func SymmetricEncrypt(ciph cipher.Block, src []byte) []byte {
+	// get a random IV and ECB encrypt it
+	iv := make([]byte, aes.BlockSize, aes.BlockSize)
+	_, err := rand.Read(iv)
+	if err != nil {
+		panic(err)
+	}
+	encryptedIv := make([]byte, aes.BlockSize, aes.BlockSize)
+	newECBEncrypter(ciph).CryptBlocks(encryptedIv, iv)
+
+	// pad it, copy the IV to the first 16 bytes and encrypt the rest with CBC
+	encrypted := padPKCS7WithIV(src)
+	copy(encrypted, encryptedIv)
+	cipher.NewCBCEncrypter(ciph, iv).CryptBlocks(encrypted[aes.BlockSize:], encrypted[aes.BlockSize:])
+	return encrypted
+}
+
+// Decrypts data from the reader using AES/CBC/PKCS7 with an IV
+// prepended using AES/ECB/None. The src slice may not be used anymore.
+func SymmetricDecrypt(ciph cipher.Block, src []byte) []byte {
+	iv := src[:aes.BlockSize]
+	newECBDecrypter(ciph).CryptBlocks(iv, iv)
+
+	data := src[aes.BlockSize:]
+	cipher.NewCBCDecrypter(ciph, iv).CryptBlocks(data, data)
+
+	return unpadPKCS7(data)
+}