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BN_SET_FLAGS(3)       DragonFly 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 con-
     tain 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 objects
	     returned by BN_value_one(3) and by the functions documented in
	     BN_get0_nist_prime_521(3).

     BN_get_flags() interpretes 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().

     These functions are currently implemented as macros, but they are likely
     to become real functions in the future when the BIGNUM data type will be
     made opaque.


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.

DragonFly 5.5			April 29, 2018			 DragonFly 5.5

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