Cryptex | Secure secret storage and cryptographic key retrieval | Cryptography library

The structure secure_head_t only contains integers, no pointers, so you under the condition you stay on the same machine/compiler+options you can consider (cast) a pointer to a secure_head_t as a pointer to sizeof(secure_head_t) characters and the reverse without any problem. Else save/marshall the 4 integers as their external forms with sprintf or equivalent and read/unmarshall them with scanf or equivalent.

I encourage you to never hide a pointer through a typedef, so do not define typedef char* secure_t; but use char*.

Your code allocate and initialize then return a secure_head_t so the use of secure_t * being a char ** has no sense because it is not a pointer to a pointer. Perhaps you imagined that because the struct contains a struct, but the struct does not contain a pointer to a struct, so there is no two levels of pointer.

You also have a problem here :