BN_SET_FLAGS(3)            Library Functions Manual            BN_SET_FLAGS(3)

NAME
     BN_set_flags, BN_get_flags - enable and inspect flags on BIGNUM objects

SYNOPSIS
     #include <openssl/bn.h>

     void
     BN_set_flags(BIGNUM *b, int flags);

     int
     BN_get_flags(const BIGNUM *b, int flags);

DESCRIPTION
     BN_set_flags() enables the given flags on b.  The flags argument can
     contain zero or more of the following constants OR'ed together:

     BN_FLG_CONSTTIME
             If this flag is set on the divident a or the divisor d in
             BN_div(3), on the exponent p in BN_mod_exp(3), or on the divisor
             a or the modulus n in BN_mod_inverse(3), these functions select
             algorithms with an execution time independent of the respective
             numbers, to avoid exposing sensitive information to timing side-
             channel attacks.

             This flag is off by default for BIGNUM objects created with
             BN_new(3).

     BN_FLG_MALLOCED
             If this flag is set, BN_free(3) and BN_clear_free(3) will not
             only clear and free the components of b, but also b itself.  This
             flag is set internally by BN_new(3).  Setting it manually on an
             existing BIGNUM object is usually a bad idea and can cause calls
             to free(3) with bogus arguments.

     BN_FLG_STATIC_DATA
             If this flag is set, BN_clear_free(3) will neither clear nor free
             the memory used for storing the number.  Consequently, setting it
             manually on an existing BIGNUM object is usually a terrible idea
             that can cause both disclosure of secret data and memory leaks.
             This flag is automatically set on the constant BIGNUM object
             returned by BN_value_one(3).

     BN_get_flags() interprets flags as a bitmask and returns those of the
     given flags that are set in b, OR'ed together, or 0 if none of the given
     flags is set.  The flags argument has the same syntax as for
     BN_set_flags().

RETURN VALUES
     BN_get_flags() returns zero or more of the above constants, OR'ed
     together.

SEE ALSO
     BN_mod_exp(3), BN_mod_inverse(3), BN_new(3), BN_with_flags(3)

HISTORY
     BN_set_flags() and BN_get_flags() first appeared in SSLeay 0.9.1 and have
     been available since OpenBSD 2.6.

CAVEATS
     No public interface exists to clear a flag once it is set.  So think
     twice before using BN_set_flags().

BUGS
     Even if the BN_FLG_CONSTTIME flag is set on a or b, BN_gcd() neither
     fails nor operates in constant time, potentially allowing timing side-
     channel attacks.

     Even if the BN_FLG_CONSTTIME flag is set on p, if the modulus m is even,
     BN_mod_exp(3) does not operate in constant time, potentially allowing
     timing side-channel attacks.

     If BN_FLG_CONSTTIME is set on p, BN_exp() fails instead of operating in
     constant time.

Linux 6.8.2-arch2-1             April 27, 2023             Linux 6.8.2-arch2-1