[PATCH] favor bcrypt over wincrypt for the random generator on Windows

[Steve Lhomme]

Hello,

Any update on this ? This prevents libssp from being usable in UWP apps.

(BTW the name of the old API is not wincrypt, the header, but CryptoAPI 
or CAPI)

On 2020-04-21 9:48, Steve Lhomme wrote:
> BCrypt is more modern and supported in Universal Apps, Wincrypt is not and
> CryptGenRandom is deprecated:
> https://docs.microsoft.com/en-us/windows/win32/api/wincrypt/nf-wincrypt-cryptgenrandom
> 
> BCrypt is available since Vista
> https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptopenalgorithmprovider
> 
> It requires linking with bcrypt rather than advapi32 for wincrypt.
> ---
>   libssp/configure.ac | 16 ++++++++++++++++
>   libssp/ssp.c        | 20 ++++++++++++++++++++
>   2 files changed, 36 insertions(+)
> 
> diff --git a/libssp/configure.ac b/libssp/configure.ac
> index f30f81c54f6..a39d9e9c992 100644
> --- a/libssp/configure.ac
> +++ b/libssp/configure.ac
> @@ -158,6 +158,22 @@ else
>   fi
>   AC_SUBST(ssp_have_usable_vsnprintf)
>   
> +AC_ARG_ENABLE(bcrypt,
> +AS_HELP_STRING([--disable-bcrypt],
> +  [use bcrypt for random generator on Windows (otherwise wincrypt)]),
> +  use_win_bcrypt=$enableval,
> +  use_win_bcrypt=yes)
> +if test "x$use_win_bcrypt" != xno; then
> +  case "$target_os" in
> +    win32 | pe | mingw32*)
> +      AC_CHECK_TYPES([BCRYPT_ALG_HANDLE],[
> +  LDFLAGS="$LDFLAGS -lbcrypt"
> +],[],[#include <windows.h>
> +#include <bcrypt.h>])
> +    ;;
> +  esac
> +fi
> +
>   AM_PROG_LIBTOOL
>   ACX_LT_HOST_FLAGS
>   AC_SUBST(enable_shared)
> diff --git a/libssp/ssp.c b/libssp/ssp.c
> index 28f3e9cc64a..f07cc41fd4f 100644
> --- a/libssp/ssp.c
> +++ b/libssp/ssp.c
> @@ -56,7 +56,11 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
>      to the console using  "CONOUT$"   */
>   #if defined (_WIN32) && !defined (__CYGWIN__)
>   #include <windows.h>
> +#ifdef HAVE_BCRYPT_ALG_HANDLE
> +#include <bcrypt.h>
> +#else
>   #include <wincrypt.h>
> +#endif
>   # define _PATH_TTY "CONOUT$"
>   #else
>   # define _PATH_TTY "/dev/tty"
> @@ -77,6 +81,21 @@ __guard_setup (void)
>       return;
>   
>   #if defined (_WIN32) && !defined (__CYGWIN__)
> +#ifdef HAVE_BCRYPT_ALG_HANDLE
> +  BCRYPT_ALG_HANDLE algo = 0;
> +  NTSTATUS err = BCryptOpenAlgorithmProvider(&algo, BCRYPT_RNG_ALGORITHM,
> +                                             NULL, 0);
> +  if (BCRYPT_SUCCESS(err))
> +    {
> +      if (BCryptGenRandom(algo, (BYTE *)&__stack_chk_guard,
> +                          sizeof (__stack_chk_guard), 0) && __stack_chk_guard != 0)
> +        {
> +           BCryptCloseAlgorithmProvider(algo, 0);
> +           return;
> +        }
> +      BCryptCloseAlgorithmProvider(algo, 0);
> +    }
> +#else /* !HAVE_BCRYPT_ALG_HANDLE */
>     HCRYPTPROV hprovider = 0;
>     if (CryptAcquireContext(&hprovider, NULL, NULL, PROV_RSA_FULL,
>                             CRYPT_VERIFYCONTEXT | CRYPT_SILENT))
> @@ -89,6 +108,7 @@ __guard_setup (void)
>           }
>         CryptReleaseContext(hprovider, 0);
>       }
> +#endif /* !HAVE_BCRYPT_ALG_HANDLE */
>   #else
>     int fd = open ("/dev/urandom", O_RDONLY);
>     if (fd != -1)
> -- 
> 2.17.1
>