[openssl-users] Questions about Ciphers

[Matt Caswell]

On 14/02/2019 16:42, Patrice Guérin wrote:
> Hello,
> 
> I have two questions :
> 
>   * I use OBJ_NAME_do_all_sorted() with  OBJ_NAME_TYPE_CIPHER_METH to get the
>     list of supported cipher methods
>     Is there a difference between lowercase and uppercase names ?
>     I've noticed that some do not have uppercase name (ex. aes-128-ccm)
>     Is there a prefered name to use ?

Objects have a "short name" and a "long name". In many cases the two are
identical. In others they have minor differences such as uppercase vs lowercase.
It doesn't matter - both forms refer to the same object. You can use either.

>   * In the case of GCM usage (with examples found in the OpenSSL wiki),
>     Is the specific control action to set the tag on decryption can be done at
>     the beginning rather than juste before EVP_DecryptFinal_ex() ?

Yes, as long as it's done after EVP_DecryptInit_ex().

Matt