Re: OpenSSL AES Decryption fails randomly C++

[Thomas Bailleux <thomas.bailleux@xxxxxxxxxxxxxxxxxx>]

Hello Jinze.

The issue doesn't come from OpenSSL. It comes from at least two buffer overruns.

In aesEncrypt:

ret = EVP_EncryptInit_ex(ctx, EVP_aes_128_ecb(), NULL, (const unsigned char*)key.c_str(), NULL);

You use key.c_str() to set the key. However, key here is "input":

if (!aesEncrypt(content, "input", encrypted_content)) return -1;

key.c_str() returns a buffer of size 6: "input" plus the null-terminated byte. However, EVP_aes_128_ecb expects a buffer of at least 16 bytes.

Therefore, this is UB: you don't control the 10 bytes after the buffer returned by key.c_str().

Same with aesDecrypt:

ret = EVP_DecryptInit_ex(ctx, EVP_aes_128_ecb(), NULL, (const unsigned char*)key.c_str(), NULL); 

if (!aesDecrypt(encrypted_content, "input", decrypted_content)) {

If you set "input" to "AAAAAAAAAAAAAAAA" ("A" x 16), it works.

The main issue here is that you use the wrong container for storing your key materials and your buffers. You should use "std::vector<std::byte>" (or "std::vector<uint8_t>") with std::vector::data().

Regards,

On 12 Nov 2022, at 11:25, WuJinze via openssl-users <openssl-users@xxxxxxxxxxx> wrote:

sorry for my mistake. I found that the gist url can not display well in mail and here is the url: https://gist.github.com/GoGim1/77c9bebec1cc71cea066515b4623a051

WuJinze
294843472@xxxxxx
 

------------------ Original ------------------
From: "WuJinze" <294843472@xxxxxx>;
Date: Sat, Nov 12, 2022 06:17 PM
To: "openssl-users"<openssl-users@xxxxxxxxxxx>;Subject: OpenSSL AES Decryption fails randomly C++

Dear OpenSSL Group,
Greetings. I was working on writing simple aes encrypt/decrypt wrapper function in c++ and running into a strange problem. The minimal reproducible examples in gist seems working fine but when i uncomment lines 90-92, it will fail to decrypt randomly. Can someone help me to figure out what's wrong with the code?
Here is my code: OpenSSL AES Decryption fails randomly C++ (github.com). OpenSSL version is OpenSSL 1.1.1f. G++ version is 9.4.0.
Regards,
Jinze