BN_CTX_START(3)            Library Functions Manual            BN_CTX_START(3)

NAME
     BN_CTX_start, BN_CTX_get, BN_CTX_end - use temporary BIGNUM variables

SYNOPSIS
     #include <openssl/bn.h>

     void
     BN_CTX_start(BN_CTX *ctx);

     BIGNUM *
     BN_CTX_get(BN_CTX *ctx);

     void
     BN_CTX_end(BN_CTX *ctx);

DESCRIPTION
     These functions are used to obtain temporary BIGNUM variables from a
     BN_CTX (which can be created using BN_CTX_new(3)) in order to save the
     overhead of repeatedly creating and freeing BIGNUMs in functions that are
     called from inside a loop.

     A function must call BN_CTX_start() first.  Then, BN_CTX_get() may be
     called repeatedly to obtain temporary BIGNUMs.  All BN_CTX_get() calls
     must be made before calling any other functions that use the ctx as an
     argument.

     Finally, BN_CTX_end() must be called before returning from the function.
     When BN_CTX_end() is called, the BIGNUM pointers obtained from
     BN_CTX_get() become invalid.  If ctx is NULL, no action occurs.

RETURN VALUES
     BN_CTX_get() returns a pointer to the BIGNUM, or NULL on error.  Once
     BN_CTX_get() has failed, the subsequent calls will return NULL as well,
     so it is sufficient to check the return value of the last BN_CTX_get()
     call.  In case of an error, an error code is set which can be obtained by
     ERR_get_error(3).

SEE ALSO
     BN_CTX_new(3), BN_new(3)

HISTORY
     BN_CTX_start(), BN_CTX_get(), and BN_CTX_end() first appeared in OpenSSL
     0.9.5 and have been available since OpenBSD 2.7.

Linux 6.8.2-arch2-1             August 20, 2019            Linux 6.8.2-arch2-1