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 #include <openssl/bio.h>
10 #include <openssl/evp.h>
11
12 BIO_METHOD *	BIO_f_md(void);
13 int BIO_set_md(BIO *b,EVP_MD *md);
14 int BIO_get_md(BIO *b,EVP_MD **mdp);
15 int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp);
16
17=head1 DESCRIPTION
18
19BIO_f_md() returns the message digest BIO method. This is a filter
20BIO that digests any data passed through it, it is a BIO wrapper
21for the digest routines EVP_DigestInit(), EVP_DigestUpdate()
22and EVP_DigestFinal().
23
24Any data written or read through a digest BIO using BIO_read() and
25BIO_write() is digested.
26
27BIO_gets(), if its B<size> parameter is large enough finishes the
28digest calculation and returns the digest value. BIO_puts() is
29not supported.
30
31BIO_reset() reinitialises a digest BIO.
32
33BIO_set_md() sets the message digest of BIO B<b> to B<md>: this
34must be called to initialize a digest BIO before any data is
35passed through it. It is a BIO_ctrl() macro.
36
37BIO_get_md() places the a pointer to the digest BIOs digest method
38in B<mdp>, it is a BIO_ctrl() macro.
39
40BIO_get_md_ctx() returns the digest BIOs context into B<mdcp>.
41
42=head1 NOTES
43
44The context returned by BIO_get_md_ctx() can be used in calls
45to EVP_DigestFinal() and also the signature routines EVP_SignFinal()
46and EVP_VerifyFinal().
47
48The context returned by BIO_get_md_ctx() is an internal context
49structure. Changes made to this context will affect the digest
50BIO itself and the context pointer will become invalid when the digest
51BIO is freed.
52
53After the digest has been retrieved from a digest BIO it must be
54reinitialized by calling BIO_reset(), or BIO_set_md() before any more
55data is passed through it.
56
57If an application needs to call BIO_gets() or BIO_puts() through
58a chain containing digest BIOs then this can be done by prepending
59a buffering BIO.
60
61Before OpenSSL 1.0.0 the call to BIO_get_md_ctx() would only work if the BIO
62had been initialized for example by calling BIO_set_md() ). In OpenSSL
631.0.0 and later the context is always returned and the BIO is state is set
64to initialized. 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
720 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 bio = BIO_new(BIO_s_null());
83 mdtmp = BIO_new(BIO_f_md());
84 BIO_set_md(mdtmp, EVP_sha1());
85 /* For BIO_push() we want to append the sink BIO and keep a note of
86  * the start of the chain.
87  */
88 bio = BIO_push(mdtmp, bio);
89 mdtmp = BIO_new(BIO_f_md());
90 BIO_set_md(mdtmp, EVP_md5());
91 bio = BIO_push(mdtmp, bio);
92 /* Note: mdtmp can now be discarded */
93 BIO_write(bio, message, strlen(message));
94
95The next example digests data by reading through a chain instead:
96
97 BIO *bio, *mdtmp;
98 char buf[1024];
99 int rdlen;
100 bio = BIO_new_file(file, "rb");
101 mdtmp = BIO_new(BIO_f_md());
102 BIO_set_md(mdtmp, EVP_sha1());
103 bio = BIO_push(mdtmp, bio);
104 mdtmp = BIO_new(BIO_f_md());
105 BIO_set_md(mdtmp, EVP_md5());
106 bio = BIO_push(mdtmp, bio);
107 do {
108 	rdlen = BIO_read(bio, buf, sizeof(buf));
109        /* Might want to do something with the data here */
110 } while(rdlen > 0);
111
112This next example retrieves the message digests from a BIO chain and
113outputs them. This could be used with the examples above.
114
115 BIO *mdtmp;
116 unsigned char mdbuf[EVP_MAX_MD_SIZE];
117 int mdlen;
118 int i;
119 mdtmp = bio;	/* Assume bio has previously been set up */
120 do {
121	EVP_MD *md;
122 	mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
123        if(!mdtmp) break;
124	BIO_get_md(mdtmp, &md);
125        printf("%s digest", OBJ_nid2sn(EVP_MD_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
134=head1 BUGS
135
136The lack of support for BIO_puts() and the non standard behaviour of
137BIO_gets() could be regarded as anomalous. It could be argued that BIO_gets()
138and BIO_puts() should be passed to the next BIO in the chain and digest
139the data passed through and that digests should be retrieved using a
140separate BIO_ctrl() call.
141
142=head1 SEE ALSO
143
144TBA
145