Handle malformed encrypted requests without panics

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

pkg/encrypt/aes.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"crypto/aes"
 	"crypto/cipher"
+	"fmt"
 )
 
 var (
@@ -17,32 +18,45 @@ func padding(plainText []byte, blockSize int) []byte {
 	return plainText
 }
 
-func unPadding(cipherText []byte) []byte {
+func unPadding(cipherText []byte) ([]byte, error) {
+	if len(cipherText) == 0 {
+		return nil, fmt.Errorf("AES plaintext is empty")
+	}
+
 	end := cipherText[len(cipherText)-1]
-	cipherText = cipherText[:len(cipherText)-int(end)]
-	return cipherText
+	if end == 0 || int(end) > len(cipherText) {
+		return nil, fmt.Errorf("invalid AES padding")
+	}
+	for _, value := range cipherText[len(cipherText)-int(end):] {
+		if value != end {
+			return nil, fmt.Errorf("invalid AES padding")
+		}
+	}
+	return cipherText[:len(cipherText)-int(end)], nil
 }
 
-func AESCBCEncrypt(plainText []byte, key []byte) []byte {
+func AESCBCEncrypt(plainText []byte, key []byte) ([]byte, error) {
 	block, err := aes.NewCipher(key)
 	if err != nil {
-		panic(err)
+		return nil, err
 	}
 	plainText = padding(plainText, block.BlockSize())
 	blockMode := cipher.NewCBCEncrypter(block, iv)
 	cipherText := make([]byte, len(plainText))
 	blockMode.CryptBlocks(cipherText, plainText)
-	return cipherText
+	return cipherText, nil
 }
 
-func AESCBCDecrypt(cipherText []byte, key []byte) []byte {
+func AESCBCDecrypt(cipherText []byte, key []byte) ([]byte, error) {
 	block, err := aes.NewCipher(key)
 	if err != nil {
-		panic(err)
+		return nil, err
+	}
+	if len(cipherText) == 0 || len(cipherText)%block.BlockSize() != 0 {
+		return nil, fmt.Errorf("AES ciphertext must be a non-empty multiple of the block size")
 	}
 	plainText := make([]byte, len(cipherText))
 	blockMode := cipher.NewCBCDecrypter(block, iv)
 	blockMode.CryptBlocks(plainText, cipherText)
-	plainText = unPadding(plainText)
-	return plainText
+	return unPadding(plainText)
 }