Re: AES-256-XTS related question on a multithreaded program

[Dim Xr <dimxrss@xxxxxxxxx>]

To answer my own question, after checking the documentation,

I think that the answer is NO, you can't give the same buffers

to multiple threads.

I would appreciate if anyone can confirm this, because I've faced

some pretty weird bugs (which are not deterministic, I mean in the

most cases my program seems to work correctly, but in some cases

it doesn't) and I can't find why!

"In particular, being configured for threads support does not

imply that all OpenSSL objects are thread-safe.

To emphasize: most objects are not safe for simultaneous use."

From: https://www.openssl.org/docs/man3.0/man7/openssl-threads.html

On Thu, Jul 20, 2023 at 12:21 AM Dim Xr <dimxrss@xxxxxxxxx> wrote:

Hi all!

At the moment I'm experimenting with OpenSSL-3.1.0, and I'm

trying to encrypt in parallel a block of data.

Let's say that I have a block of 4096 bytes stored in a buffer.

Can I pass to worker threads a pointer to this buffer (let' call

it input_buf), a pointer to an output buffer (let's call it output_buf)

 and a corresponding tweak value and let them work in parallel?

So each thread (in short) will compute something like (error handling

is abbreviated):

cipher = EVP_CIPHER_fetch(NULL, "AES-256-XTS", NULL);

EVP_EncryptInit_ex2(ctx, cipher, key, NULL, NULL);

EVP_EncryptInit_ex2(ctx, NULL, NULL, tweak, NULL);

EVP_EncryptUpdate(ctx, outbuf + relative_bytes, &encrypt_size,

input_buf + relative_bytes, inputsize);

To put it another way, can multiple threads work **on the same

input and output buffers** (but in different regions of course) in

parallel?

Thanks,

Dimitris