1.\" $OpenBSD: BIO_f_md.3,v 1.11 2019/06/06 01:06:58 schwarze Exp $ 2.\" OpenSSL a528d4f0 Oct 27 13:40:11 2015 -0400 3.\" 4.\" This file was written by Dr. Stephen Henson <steve@openssl.org>. 5.\" Copyright (c) 2000, 2006, 2009, 2016 The OpenSSL Project. 6.\" All rights reserved. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in 17.\" the documentation and/or other materials provided with the 18.\" distribution. 19.\" 20.\" 3. 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Redistributions of any form whatsoever must retain the following 35.\" acknowledgment: 36.\" "This product includes software developed by the OpenSSL Project 37.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)" 38.\" 39.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY 40.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 41.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 42.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR 43.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 44.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 45.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 46.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 47.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 48.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 49.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 50.\" OF THE POSSIBILITY OF SUCH DAMAGE. 51.\" 52.Dd $Mdocdate: June 6 2019 $ 53.Dt BIO_F_MD 3 54.Os 55.Sh NAME 56.Nm BIO_f_md , 57.Nm BIO_set_md , 58.Nm BIO_get_md , 59.Nm BIO_get_md_ctx 60.Nd message digest BIO filter 61.Sh SYNOPSIS 62.In openssl/bio.h 63.In openssl/evp.h 64.Ft const BIO_METHOD * 65.Fo BIO_f_md 66.Fa void 67.Fc 68.Ft int 69.Fo BIO_set_md 70.Fa "BIO *b" 71.Fa "EVP_MD *md" 72.Fc 73.Ft int 74.Fo BIO_get_md 75.Fa "BIO *b" 76.Fa "EVP_MD **mdp" 77.Fc 78.Ft int 79.Fo BIO_get_md_ctx 80.Fa "BIO *b" 81.Fa "EVP_MD_CTX **mdcp" 82.Fc 83.Sh DESCRIPTION 84.Fn BIO_f_md 85returns the message digest BIO method. 86This is a filter BIO that digests any data passed through it. 87It is a BIO wrapper for the digest routines 88.Xr EVP_DigestInit 3 , 89.Xr EVP_DigestUpdate 3 , 90and 91.Xr EVP_DigestFinal 3 . 92.Pp 93Any data written or read through a digest BIO using 94.Xr BIO_read 3 95and 96.Xr BIO_write 3 97is digested. 98.Pp 99.Xr BIO_gets 3 , 100if its 101.Sy size 102parameter is large enough, 103finishes the digest calculation and returns the digest value. 104.Xr BIO_puts 3 105is 106not supported. 107.Pp 108.Xr BIO_reset 3 109reinitialises a digest BIO. 110.Pp 111.Fn BIO_set_md 112sets the message digest of BIO 113.Fa b 114to 115.Fa md : 116this must be called to initialize a digest BIO 117before any data is passed through it. 118It is a 119.Xr BIO_ctrl 3 120macro. 121.Pp 122.Fn BIO_get_md 123places a pointer to the digest BIOs digest method in 124.Fa mdp . 125It is a 126.Xr BIO_ctrl 3 127macro. 128.Pp 129.Fn BIO_get_md_ctx 130returns the digest BIOs context in 131.Fa mdcp . 132.Pp 133The context returned by 134.Fn BIO_get_md_ctx 135can be used in calls to 136.Xr EVP_DigestFinal 3 137and also in the signature routines 138.Xr EVP_SignFinal 3 139and 140.Xr EVP_VerifyFinal 3 . 141.Pp 142The context returned by 143.Fn BIO_get_md_ctx 144is an internal context structure. 145Changes made to this context will affect the digest BIO itself, and 146the context pointer will become invalid when the digest BIO is freed. 147.Pp 148After the digest has been retrieved from a digest BIO, 149it must be reinitialized by calling 150.Xr BIO_reset 3 151or 152.Fn BIO_set_md 153before any more data is passed through it. 154.Pp 155If an application needs to call 156.Xr BIO_gets 3 157or 158.Xr BIO_puts 3 159through a chain containing digest BIOs, 160then this can be done by prepending a buffering BIO. 161.Pp 162Calling 163.Fn BIO_get_md_ctx 164will return the context and initialize the 165.Vt BIO 166state. 167This allows applications to initialize the context externally 168if the standard calls such as 169.Fn BIO_set_md 170are not sufficiently flexible. 171.Sh RETURN VALUES 172.Fn BIO_f_md 173returns the digest BIO method. 174.Pp 175.Fn BIO_set_md , 176.Fn BIO_get_md , 177and 178.Fn BIO_get_md_ctx 179return 1 for success and 0 for failure. 180.Sh EXAMPLES 181The following example creates a BIO chain containing a SHA-1 and MD5 182digest BIO and passes the string "Hello World" through it. 183Error checking has been omitted for clarity. 184.Bd -literal -offset 2n 185BIO *bio, *mdtmp; 186const char message[] = "Hello World"; 187bio = BIO_new(BIO_s_null()); 188mdtmp = BIO_new(BIO_f_md()); 189BIO_set_md(mdtmp, EVP_sha1()); 190/* 191 * For BIO_push() we want to append the sink BIO 192 * and keep a note of the start of the chain. 193 */ 194bio = BIO_push(mdtmp, bio); 195mdtmp = BIO_new(BIO_f_md()); 196BIO_set_md(mdtmp, EVP_md5()); 197bio = BIO_push(mdtmp, bio); 198/* Note: mdtmp can now be discarded */ 199BIO_write(bio, message, strlen(message)); 200.Ed 201.Pp 202The next example digests data by reading through a chain instead: 203.Bd -literal -offset 2n 204BIO *bio, *mdtmp; 205char buf[1024]; 206int rdlen; 207 208bio = BIO_new_file(file, "rb"); 209mdtmp = BIO_new(BIO_f_md()); 210BIO_set_md(mdtmp, EVP_sha1()); 211bio = BIO_push(mdtmp, bio); 212mdtmp = BIO_new(BIO_f_md()); 213BIO_set_md(mdtmp, EVP_md5()); 214bio = BIO_push(mdtmp, bio); 215do { 216 rdlen = BIO_read(bio, buf, sizeof(buf)); 217 /* Might want to do something with the data here */ 218} while (rdlen > 0); 219.Ed 220.Pp 221This next example retrieves the message digests from a BIO chain 222and outputs them. 223This could be used with the examples above. 224.Bd -literal -offset 2n 225BIO *mdtmp; 226unsigned char mdbuf[EVP_MAX_MD_SIZE]; 227int mdlen; 228int i; 229 230mdtmp = bio; /* Assume bio has previously been set up */ 231do { 232 EVP_MD *md; 233 mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD); 234 if (!mdtmp) 235 break; 236 BIO_get_md(mdtmp, &md); 237 printf("%s digest", OBJ_nid2sn(EVP_MD_type(md))); 238 mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE); 239 for(i = 0; i < mdlen; i++) 240 printf(":%02X", mdbuf[i]); 241 printf("\en"); 242 mdtmp = BIO_next(mdtmp); 243} while(mdtmp); 244BIO_free_all(bio); 245.Ed 246.Sh SEE ALSO 247.Xr BIO_new 3 , 248.Xr EVP_DigestInit 3 249.Sh HISTORY 250.Fn BIO_f_md , 251.Fn BIO_set_md , 252and 253.Fn BIO_get_md 254first appeared in SSLeay 0.6.0. 255.Fn BIO_get_md_ctx 256first appeared in SSLeay 0.8.1. 257These functions have been available since 258.Ox 2.4 . 259.Pp 260Before OpenSSL 1.0.0, the call to 261.Fn BIO_get_md_ctx 262would only work if the 263.Vt BIO 264had been initialized, for example by calling 265.Fn BIO_set_md . 266.Sh BUGS 267The lack of support for 268.Xr BIO_puts 3 269and the non-standard behaviour of 270.Xr BIO_gets 3 271could be regarded as anomalous. 272It could be argued that 273.Xr BIO_gets 3 274and 275.Xr BIO_puts 3 276should be passed to the next BIO in the chain and digest the data 277passed through and that digests should be retrieved using a separate 278.Xr BIO_ctrl 3 279call. 280