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BN_CTX_start(3)                                    OpenSSL                                   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 been created
       by 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.

RETURN VALUES
       BN_CTX_start() and BN_CTX_end() return no 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)

HISTORY
       BN_CTX_start(), BN_CTX_get() and BN_CTX_end() were added in OpenSSL 0.9.5.



50                                               2013-03-05                                  BN_CTX_start(3)