5 BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx - message digest BIO filter
9 =for comment multiple includes
11 #include <openssl/bio.h>
12 #include <openssl/evp.h>
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);
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().
26 Any data written or read through a digest BIO using BIO_read_ex() and
27 BIO_write_ex() is digested.
29 BIO_gets(), if its B<size> parameter is large enough finishes the
30 digest calculation and returns the digest value. BIO_puts() is
33 BIO_reset() reinitialises a digest BIO.
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.
39 BIO_get_md() places the a pointer to the digest BIOs digest method
40 in B<mdp>, it is a BIO_ctrl() macro.
42 BIO_get_md_ctx() returns the digest BIOs context into B<mdcp>.
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().
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
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.
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
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.
69 BIO_f_md() returns the digest BIO method.
71 BIO_set_md(), BIO_get_md() and BIO_md_ctx() return 1 for success and
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.
81 char message[] = "Hello World";
82 bio = BIO_new(BIO_s_null());
83 mdtmp = BIO_new(BIO_f_md());
84 BIO_set_md(mdtmp, EVP_sha1());
86 * For BIO_push() we want to append the sink BIO and keep a note of
87 * the start of the chain.
89 bio = BIO_push(mdtmp, bio);
90 mdtmp = BIO_new(BIO_f_md());
91 BIO_set_md(mdtmp, EVP_md5());
92 bio = BIO_push(mdtmp, bio);
93 /* Note: mdtmp can now be discarded */
94 BIO_write(bio, message, strlen(message));
96 The next example digests data by reading through a chain instead:
101 bio = BIO_new_file(file, "rb");
102 mdtmp = BIO_new(BIO_f_md());
103 BIO_set_md(mdtmp, EVP_sha1());
104 bio = BIO_push(mdtmp, bio);
105 mdtmp = BIO_new(BIO_f_md());
106 BIO_set_md(mdtmp, EVP_md5());
107 bio = BIO_push(mdtmp, bio);
109 rdlen = BIO_read(bio, buf, sizeof(buf));
110 /* Might want to do something with the data here */
113 This next example retrieves the message digests from a BIO chain and
114 outputs them. This could be used with the examples above.
117 unsigned char mdbuf[EVP_MAX_MD_SIZE];
120 mdtmp = bio; /* Assume bio has previously been set up */
123 mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
126 BIO_get_md(mdtmp, &md);
127 printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));
128 mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
129 for (i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);
131 mdtmp = BIO_next(mdtmp);
138 The lack of support for BIO_puts() and the non standard behaviour of
139 BIO_gets() could be regarded as anomalous. It could be argued that BIO_gets()
140 and BIO_puts() should be passed to the next BIO in the chain and digest
141 the data passed through and that digests should be retrieved using a
142 separate BIO_ctrl() call.
146 Before OpenSSL 1.0.0., the call to BIO_get_md_ctx() would only work if the
147 BIO was initialized first.
151 Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
153 Licensed under the OpenSSL license (the "License"). You may not use
154 this file except in compliance with the License. You can obtain a copy
155 in the file LICENSE in the source distribution or at
156 L<https://www.openssl.org/source/license.html>.