doc/man3/BIO_f_md.pod

   1 =pod
   2
   3 =head1 NAME
   4
   5 BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx - message digest BIO filter
   6
   7 =head1 SYNOPSIS
   8
   9 =for comment 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
  21 BIO_f_md() returns the message digest BIO method. This is a filter
  22 BIO that digests any data passed through it, it is a BIO wrapper
  23 for the digest routines EVP_DigestInit(), EVP_DigestUpdate()
  24 and EVP_DigestFinal().
  25
  26 Any data written or read through a digest BIO using BIO_read_ex() and
  27 BIO_write_ex() is digested.
  28
  29 BIO_gets(), if its B<size> parameter is large enough finishes the
  30 digest calculation and returns the digest value. BIO_puts() is
  31 not supported.
  32
  33 BIO_reset() reinitialises a digest BIO.
  34
  35 BIO_set_md() sets the message digest of BIO B<b> to B<md>: this
  36 must be called to initialize a digest BIO before any data is
  37 passed through it. It is a BIO_ctrl() macro.
  38
  39 BIO_get_md() places the a pointer to the digest BIOs digest method
  40 in B<mdp>, it is a BIO_ctrl() macro.
  41
  42 BIO_get_md_ctx() returns the digest BIOs context into B<mdcp>.
  43
  44 =head1 NOTES
  45
  46 The context returned by BIO_get_md_ctx() can be used in calls
  47 to EVP_DigestFinal() and also the signature routines EVP_SignFinal()
  48 and EVP_VerifyFinal().
  49
  50 The context returned by BIO_get_md_ctx() is an internal context
  51 structure. Changes made to this context will affect the digest
  52 BIO itself and the context pointer will become invalid when the digest
  53 BIO is freed.
  54
  55 After the digest has been retrieved from a digest BIO it must be
  56 reinitialized by calling BIO_reset(), or BIO_set_md() before any more
  57 data is passed through it.
  58
  59 If an application needs to call BIO_gets() or BIO_puts() through
  60 a chain containing digest BIOs then this can be done by prepending
  61 a buffering BIO.
  62
  63 Calling BIO_get_md_ctx() will return the context and initialize the BIO
  64 state. This allows applications to initialize the context externally
  65 if the standard calls such as BIO_set_md() are not sufficiently flexible.
  66
  67 =head1 RETURN VALUES
  68
  69 BIO_f_md() returns the digest BIO method.
  70
  71 BIO_set_md(), BIO_get_md() and BIO_md_ctx() return 1 for success and
  72 0 for failure.
  73
  74 =head1 EXAMPLES
  75
  76 The following example creates a BIO chain containing an SHA1 and MD5
  77 digest BIO and passes the string "Hello World" through it. Error
  78 checking 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
  97 The 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
 115 This next example retrieves the message digests from a BIO chain and
 116 outputs 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_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
 142 The lack of support for BIO_puts() and the non standard behaviour of
 143 BIO_gets() could be regarded as anomalous. It could be argued that BIO_gets()
 144 and BIO_puts() should be passed to the next BIO in the chain and digest
 145 the data passed through and that digests should be retrieved using a
 146 separate BIO_ctrl() call.
 147
 148 =head1 HISTORY
 149
 150 Before OpenSSL 1.0.0., the call to BIO_get_md_ctx() would only work if the
 151 BIO was initialized first.
 152
 153 =head1 COPYRIGHT
 154
 155 Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
 156
 157 Licensed under the Apache License 2.0 (the "License").  You may not use
 158 this file except in compliance with the License.  You can obtain a copy
 159 in the file LICENSE in the source distribution or at
 160 L<https://www.openssl.org/source/license.html>.
 161
 162 =cut