ptr = sodium_malloc(size) returns a pointer from which exactly "size" bytes
can be accessed.
ptr = sodium_allocarray(count, size) allocates enough storage space for
"count" pointers or scalars of unit size "size".
In both cases, the region is immediately followed by a guard page.
As a result, any attempt to access a memory location after ptr[size - 1] will
immediately trigger a segmentation fault.
The allocated region is mlock()ed and filled with 0xd0 bytes.
A read-only page with the size, a guard page, as well as a canary are
placed before the returned pointer.
The canary is checked by sodium_free(); as a result, altering data right
before ptr is likely to cause sodium_free() to kill the process.
sodium_free() munlock()s the region and fills it with zeros before
actually calling free().
sodium_mprotect_noaccess(), sodium_mprotect_readonly() and
sodium_mprotect_readwrite() can be used to change the protection on the set
of allocated pages.
Reverting the protection to read+write is not required before calling
sodium_free().
Encrypting in-place and storing the tag separately is a very common need.
Instead of forcing people to do their own cuisine, let's provide simple
variants of the _easy interfaces to do that.
crypto_sign() doesn't just need the secret key. The public key has to follow.
Which is why the test vectors are laid out in this order.
But this can confuse static analysis, as well as people looking at the test
in order to better understand how crypto_sign() works.
So, just copy the sk and the pk into a dedicated buffer, for clarity.
- Moved variable declarations to top of function
- Constant output buffer inside the function
Moved strlen calls from main to inside function to make code easier to read.
Also switched from fancy quotes to single quotes in expected output
Frank Denis