1BIO_F_MD(3ossl)                     OpenSSL                    BIO_F_MD(3ossl)
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NAME

6       BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx - message digest BIO
7       filter
8

SYNOPSIS

10        #include <openssl/bio.h>
11        #include <openssl/evp.h>
12
13        const BIO_METHOD *BIO_f_md(void);
14        int BIO_set_md(BIO *b, EVP_MD *md);
15        int BIO_get_md(BIO *b, EVP_MD **mdp);
16        int BIO_get_md_ctx(BIO *b, EVP_MD_CTX **mdcp);
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DESCRIPTION

19       BIO_f_md() returns the message digest BIO method. This is a filter BIO
20       that digests any data passed through it, it is a BIO wrapper for the
21       digest routines EVP_DigestInit(), EVP_DigestUpdate() and
22       EVP_DigestFinal().
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24       Any data written or read through a digest BIO using BIO_read_ex() and
25       BIO_write_ex() is digested.
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27       BIO_gets(), if its size parameter is large enough finishes the digest
28       calculation and returns the digest value. BIO_puts() is not supported.
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30       BIO_reset() reinitialises a digest BIO.
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32       BIO_set_md() sets the message digest of BIO b to md: this must be
33       called to initialize a digest BIO before any data is passed through it.
34       It is a BIO_ctrl() macro.
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36       BIO_get_md() places the a pointer to the digest BIOs digest method in
37       mdp, it is a BIO_ctrl() macro.
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39       BIO_get_md_ctx() returns the digest BIOs context into mdcp.
40

NOTES

42       The context returned by BIO_get_md_ctx() can be used in calls to
43       EVP_DigestFinal() and also the signature routines EVP_SignFinal() and
44       EVP_VerifyFinal().
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46       The context returned by BIO_get_md_ctx() is an internal context
47       structure. Changes made to this context will affect the digest BIO
48       itself and the context pointer will become invalid when the digest BIO
49       is freed.
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51       After the digest has been retrieved from a digest BIO it must be
52       reinitialized by calling BIO_reset(), or BIO_set_md() before any more
53       data is passed through it.
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55       If an application needs to call BIO_gets() or BIO_puts() through a
56       chain containing digest BIOs then this can be done by prepending a
57       buffering BIO.
58
59       Calling BIO_get_md_ctx() will return the context and initialize the BIO
60       state. This allows applications to initialize the context externally if
61       the standard calls such as BIO_set_md() are not sufficiently flexible.
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RETURN VALUES

64       BIO_f_md() returns the digest BIO method.
65
66       BIO_set_md(), BIO_get_md() and BIO_md_ctx() return 1 for success and
67       <=0 for failure.
68

EXAMPLES

70       The following example creates a BIO chain containing an SHA1 and MD5
71       digest BIO and passes the string "Hello World" through it. Error
72       checking has been omitted for clarity.
73
74        BIO *bio, *mdtmp;
75        char message[] = "Hello World";
76
77        bio = BIO_new(BIO_s_null());
78        mdtmp = BIO_new(BIO_f_md());
79        BIO_set_md(mdtmp, EVP_sha1());
80        /*
81         * For BIO_push() we want to append the sink BIO and keep a note of
82         * the start of the chain.
83         */
84        bio = BIO_push(mdtmp, bio);
85        mdtmp = BIO_new(BIO_f_md());
86        BIO_set_md(mdtmp, EVP_md5());
87        bio = BIO_push(mdtmp, bio);
88        /* Note: mdtmp can now be discarded */
89        BIO_write(bio, message, strlen(message));
90
91       The next example digests data by reading through a chain instead:
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93        BIO *bio, *mdtmp;
94        char buf[1024];
95        int rdlen;
96
97        bio = BIO_new_file(file, "rb");
98        mdtmp = BIO_new(BIO_f_md());
99        BIO_set_md(mdtmp, EVP_sha1());
100        bio = BIO_push(mdtmp, bio);
101        mdtmp = BIO_new(BIO_f_md());
102        BIO_set_md(mdtmp, EVP_md5());
103        bio = BIO_push(mdtmp, bio);
104        do {
105            rdlen = BIO_read(bio, buf, sizeof(buf));
106            /* Might want to do something with the data here */
107        } while (rdlen > 0);
108
109       This next example retrieves the message digests from a BIO chain and
110       outputs them. This could be used with the examples above.
111
112        BIO *mdtmp;
113        unsigned char mdbuf[EVP_MAX_MD_SIZE];
114        int mdlen;
115        int i;
116
117        mdtmp = bio;   /* Assume bio has previously been set up */
118        do {
119            EVP_MD *md;
120
121            mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
122            if (!mdtmp)
123                break;
124            BIO_get_md(mdtmp, &md);
125            printf("%s digest", OBJ_nid2sn(EVP_MD_get_type(md)));
126            mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
127            for (i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);
128            printf("\n");
129            mdtmp = BIO_next(mdtmp);
130        } while (mdtmp);
131
132        BIO_free_all(bio);
133

BUGS

135       The lack of support for BIO_puts() and the non standard behaviour of
136       BIO_gets() could be regarded as anomalous. It could be argued that
137       BIO_gets() and BIO_puts() should be passed to the next BIO in the chain
138       and digest the data passed through and that digests should be retrieved
139       using a separate BIO_ctrl() call.
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HISTORY

142       Before OpenSSL 1.0.0., the call to BIO_get_md_ctx() would only work if
143       the BIO was initialized first.
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146       Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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148       Licensed under the Apache License 2.0 (the "License").  You may not use
149       this file except in compliance with the License.  You can obtain a copy
150       in the file LICENSE in the source distribution or at
151       <https://www.openssl.org/source/license.html>.
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1553.0.9                             2023-07-27                   BIO_F_MD(3ossl)
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