SIGSEGV from EVP_MAC_CTX_get_mac_size()

[James Muir]

On 2023-11-27 18:25, Hal Murray wrote:
> I have a fresh ctx using cmac with AES-128-CBC all ready to go.
> No key yet.
> 
> If I call EVP_MAC_CTX_get_mac_size(), I get a SIGSEGV.
> If I call EVP_MAC_init() with a key first, it works.
> 
> Is this a bug?  Is there a setup step I've missed?

Without seeing the rest of your code it is difficult to tell.

The documentation

   https://www.openssl.org/docs/man3.1/man3/EVP_MAC_CTX_get_mac_size.html

says:

 > EVP_MAC_CTX_get_mac_size() returns the expected output size, or 0 if 
it isn't set. If it isn't set, a call to EVP_MAC_init() will set it.

Do you check the return value of EVP_MAC_CTX_get_mac_size()?

Note that EVP_MAC_CTX_get_mac_size() does not seem to be called in the 
back-trace you listed.

-James M