Handle malformed encrypted requests without panics

Signed-off-by: Sean Du <do4suki@gmail.com>

pkg/encrypt/aes_test.go

@@ -0,0 +1,36 @@
+package encrypt
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestAESCBCDecryptRoundTrip(t *testing.T) {
+	key := []byte("1234567890abcdef")
+	plainText := []byte("login payload")
+
+	cipherText, err := AESCBCEncrypt(plainText, key)
+	if err != nil {
+		t.Fatalf("encrypt: %v", err)
+	}
+	decrypted, err := AESCBCDecrypt(cipherText, key)
+	if err != nil {
+		t.Fatalf("decrypt: %v", err)
+	}
+	if !bytes.Equal(decrypted, plainText) {
+		t.Fatalf("decrypted plaintext = %q, want %q", decrypted, plainText)
+	}
+}
+
+func TestAESCBCDecryptRejectsMalformedCiphertext(t *testing.T) {
+	key := []byte("1234567890abcdef")
+	for _, cipherText := range [][]byte{nil, make([]byte, 15)} {
+		if _, err := AESCBCDecrypt(cipherText, key); err == nil {
+			t.Fatalf("AESCBCDecrypt(%d bytes) succeeded", len(cipherText))
+		}
+	}
+
+	if _, err := unPadding([]byte{1, 2, 3, 2}); err == nil {
+		t.Fatal("unPadding accepted invalid padding")
+	}
+}