1.\" $OpenBSD: BN_CTX_start.3,v 1.8 2019/08/20 10:59:09 schwarze Exp $ 2.\" full merge up to: OpenSSL 35fd9953 May 28 14:49:38 2019 +0200 3.\" 4.\" This file was written by Ulf Moeller <ulf@openssl.org>. 5.\" Copyright (c) 2000 The OpenSSL Project. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in 16.\" the documentation and/or other materials provided with the 17.\" distribution. 18.\" 19.\" 3. All advertising materials mentioning features or use of this 20.\" software must display the following acknowledgment: 21.\" "This product includes software developed by the OpenSSL Project 22.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)" 23.\" 24.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to 25.\" endorse or promote products derived from this software without 26.\" prior written permission. For written permission, please contact 27.\" openssl-core@openssl.org. 28.\" 29.\" 5. Products derived from this software may not be called "OpenSSL" 30.\" nor may "OpenSSL" appear in their names without prior written 31.\" permission of the OpenSSL Project. 32.\" 33.\" 6. Redistributions of any form whatsoever must retain the following 34.\" acknowledgment: 35.\" "This product includes software developed by the OpenSSL Project 36.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)" 37.\" 38.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY 39.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 40.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 41.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR 42.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 43.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 44.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 45.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 46.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 47.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 48.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 49.\" OF THE POSSIBILITY OF SUCH DAMAGE. 50.\" 51.Dd $Mdocdate: August 20 2019 $ 52.Dt BN_CTX_START 3 53.Os 54.Sh NAME 55.Nm BN_CTX_start , 56.Nm BN_CTX_get , 57.Nm BN_CTX_end 58.Nd use temporary BIGNUM variables 59.Sh SYNOPSIS 60.In openssl/bn.h 61.Ft void 62.Fo BN_CTX_start 63.Fa "BN_CTX *ctx" 64.Fc 65.Ft BIGNUM * 66.Fo BN_CTX_get 67.Fa "BN_CTX *ctx" 68.Fc 69.Ft void 70.Fo BN_CTX_end 71.Fa "BN_CTX *ctx" 72.Fc 73.Sh DESCRIPTION 74These functions are used to obtain temporary 75.Vt BIGNUM 76variables from a 77.Vt BN_CTX 78(which can be created using 79.Xr BN_CTX_new 3 ) 80in order to save the overhead of repeatedly creating and freeing 81.Vt BIGNUM Ns s 82in functions that are called from inside a loop. 83.Pp 84A function must call 85.Fn BN_CTX_start 86first. 87Then, 88.Fn BN_CTX_get 89may be called repeatedly to obtain temporary 90.Vt BIGNUM Ns s . 91All 92.Fn BN_CTX_get 93calls must be made before calling any other functions that use the 94.Fa ctx 95as an argument. 96.Pp 97Finally, 98.Fn BN_CTX_end 99must be called before returning from the function. 100When 101.Fn BN_CTX_end 102is called, the 103.Vt BIGNUM 104pointers obtained from 105.Fn BN_CTX_get 106become invalid. 107If 108.Fa ctx 109is 110.Dv NULL , 111no action occurs. 112.Sh RETURN VALUES 113.Fn BN_CTX_get 114returns a pointer to the 115.Vt BIGNUM , 116or 117.Dv NULL 118on error. 119Once 120.Fn BN_CTX_get 121has failed, the subsequent calls will return 122.Dv NULL 123as well, so it is sufficient to check the return value of the last 124.Fn BN_CTX_get 125call. 126In case of an error, an error code is set which can be obtained by 127.Xr ERR_get_error 3 . 128.Sh SEE ALSO 129.Xr BN_CTX_new 3 , 130.Xr BN_new 3 131.Sh HISTORY 132.Fn BN_CTX_start , 133.Fn BN_CTX_get , 134and 135.Fn BN_CTX_end 136first appeared in OpenSSL 0.9.5 and have been available since 137.Ox 2.7 . 138