1=pod 2 3=head1 NAME 4 5BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx - message digest BIO filter 6 7=head1 SYNOPSIS 8 9=for openssl multiple includes 10 11 #include <openssl/bio.h> 12 #include <openssl/evp.h> 13 14 const BIO_METHOD *BIO_f_md(void); 15 int BIO_set_md(BIO *b, EVP_MD *md); 16 int BIO_get_md(BIO *b, EVP_MD **mdp); 17 int BIO_get_md_ctx(BIO *b, EVP_MD_CTX **mdcp); 18 19=head1 DESCRIPTION 20 21BIO_f_md() returns the message digest BIO method. This is a filter 22BIO that digests any data passed through it. It is a BIO wrapper 23for the digest routines EVP_DigestInit(), EVP_DigestUpdate() 24and EVP_DigestFinal(). 25 26Any data written or read through a digest BIO using BIO_read_ex() and 27BIO_write_ex() is digested. 28 29BIO_gets(), if its B<size> parameter is large enough finishes the 30digest calculation and returns the digest value. BIO_puts() is 31not supported. 32 33BIO_reset() reinitialises a digest BIO. 34 35BIO_set_md() sets the message digest of BIO B<b> to B<md>: this 36must be called to initialize a digest BIO before any data is 37passed through it. It is a BIO_ctrl() macro. 38 39BIO_get_md() places a pointer to the digest BIOs digest method 40in B<mdp>. It is a BIO_ctrl() macro. 41 42BIO_get_md_ctx() returns the digest BIOs context into B<mdcp>. 43 44=head1 NOTES 45 46The context returned by BIO_get_md_ctx() can be used in calls 47to EVP_DigestFinal() and also the signature routines EVP_SignFinal() 48and EVP_VerifyFinal(). 49 50The context returned by BIO_get_md_ctx() is an internal context 51structure. Changes made to this context will affect the digest 52BIO itself and the context pointer will become invalid when the digest 53BIO is freed. 54 55After the digest has been retrieved from a digest BIO it must be 56reinitialized by calling BIO_reset(), or BIO_set_md() before any more 57data is passed through it. 58 59If an application needs to call BIO_gets() or BIO_puts() through 60a chain containing digest BIOs then this can be done by prepending 61a buffering BIO. 62 63Calling BIO_get_md_ctx() will return the context and initialize the BIO 64state. This allows applications to initialize the context externally 65if the standard calls such as BIO_set_md() are not sufficiently flexible. 66 67=head1 RETURN VALUES 68 69BIO_f_md() returns the digest BIO method. 70 71BIO_set_md(), BIO_get_md() and BIO_md_ctx() return 1 for success and 72<=0 for failure. 73 74=head1 EXAMPLES 75 76The following example creates a BIO chain containing an SHA1 and MD5 77digest BIO and passes the string "Hello World" through it. Error 78checking has been omitted for clarity. 79 80 BIO *bio, *mdtmp; 81 char message[] = "Hello World"; 82 83 bio = BIO_new(BIO_s_null()); 84 mdtmp = BIO_new(BIO_f_md()); 85 BIO_set_md(mdtmp, EVP_sha1()); 86 /* 87 * For BIO_push() we want to append the sink BIO and keep a note of 88 * the start of the chain. 89 */ 90 bio = BIO_push(mdtmp, bio); 91 mdtmp = BIO_new(BIO_f_md()); 92 BIO_set_md(mdtmp, EVP_md5()); 93 bio = BIO_push(mdtmp, bio); 94 /* Note: mdtmp can now be discarded */ 95 BIO_write(bio, message, strlen(message)); 96 97The next example digests data by reading through a chain instead: 98 99 BIO *bio, *mdtmp; 100 char buf[1024]; 101 int rdlen; 102 103 bio = BIO_new_file(file, "rb"); 104 mdtmp = BIO_new(BIO_f_md()); 105 BIO_set_md(mdtmp, EVP_sha1()); 106 bio = BIO_push(mdtmp, bio); 107 mdtmp = BIO_new(BIO_f_md()); 108 BIO_set_md(mdtmp, EVP_md5()); 109 bio = BIO_push(mdtmp, bio); 110 do { 111 rdlen = BIO_read(bio, buf, sizeof(buf)); 112 /* Might want to do something with the data here */ 113 } while (rdlen > 0); 114 115This next example retrieves the message digests from a BIO chain and 116outputs them. This could be used with the examples above. 117 118 BIO *mdtmp; 119 unsigned char mdbuf[EVP_MAX_MD_SIZE]; 120 int mdlen; 121 int i; 122 123 mdtmp = bio; /* Assume bio has previously been set up */ 124 do { 125 EVP_MD *md; 126 127 mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD); 128 if (!mdtmp) 129 break; 130 BIO_get_md(mdtmp, &md); 131 printf("%s digest", OBJ_nid2sn(EVP_MD_get_type(md))); 132 mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE); 133 for (i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]); 134 printf("\n"); 135 mdtmp = BIO_next(mdtmp); 136 } while (mdtmp); 137 138 BIO_free_all(bio); 139 140=head1 BUGS 141 142The lack of support for BIO_puts() and the non standard behaviour of 143BIO_gets() could be regarded as anomalous. It could be argued that BIO_gets() 144and BIO_puts() should be passed to the next BIO in the chain and digest 145the data passed through and that digests should be retrieved using a 146separate BIO_ctrl() call. 147 148=head1 HISTORY 149 150Before OpenSSL 1.0.0., the call to BIO_get_md_ctx() would only work if the 151BIO was initialized first. 152 153=head1 COPYRIGHT 154 155Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved. 156 157Licensed under the Apache License 2.0 (the "License"). You may not use 158this file except in compliance with the License. You can obtain a copy 159in the file LICENSE in the source distribution or at 160L<https://www.openssl.org/source/license.html>. 161 162=cut 163
