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
61=head1 RETURN VALUES
62
63BIO_f_md() returns the digest BIO method.
64
65BIO_set_md(), BIO_get_md() and BIO_md_ctx() return 1 for success and
660 for failure.
67
68=head1 EXAMPLES
69
70The following example creates a BIO chain containing an SHA1 and MD5
71digest BIO and passes the string "Hello World" through it. Error
72checking has been omitted for clarity.
73
74 BIO *bio, *mdtmp;
75 char message[] = "Hello World";
76 bio = BIO_new(BIO_s_null());
77 mdtmp = BIO_new(BIO_f_md());
78 BIO_set_md(mdtmp, EVP_sha1());
79 /* For BIO_push() we want to append the sink BIO and keep a note of
80  * the start of the chain.
81  */
82 bio = BIO_push(mdtmp, bio);
83 mdtmp = BIO_new(BIO_f_md());
84 BIO_set_md(mdtmp, EVP_md5());
85 bio = BIO_push(mdtmp, bio);
86 /* Note: mdtmp can now be discarded */
87 BIO_write(bio, message, strlen(message));
88
89The next example digests data by reading through a chain instead:
90
91 BIO *bio, *mdtmp;
92 char buf[1024];
93 int rdlen;
94 bio = BIO_new_file(file, "rb");
95 mdtmp = BIO_new(BIO_f_md());
96 BIO_set_md(mdtmp, EVP_sha1());
97 bio = BIO_push(mdtmp, bio);
98 mdtmp = BIO_new(BIO_f_md());
99 BIO_set_md(mdtmp, EVP_md5());
100 bio = BIO_push(mdtmp, bio);
101 do {
102 	rdlen = BIO_read(bio, buf, sizeof(buf));
103        /* Might want to do something with the data here */
104 } while(rdlen > 0);
105
106This next example retrieves the message digests from a BIO chain and
107outputs them. This could be used with the examples above.
108
109 BIO *mdtmp;
110 unsigned char mdbuf[EVP_MAX_MD_SIZE];
111 int mdlen;
112 int i;
113 mdtmp = bio;	/* Assume bio has previously been set up */
114 do {
115	EVP_MD *md;
116 	mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
117        if(!mdtmp) break;
118	BIO_get_md(mdtmp, &md);
119        printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));
120	mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
121	for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);
122	printf("\n");
123	mdtmp = BIO_next(mdtmp);
124 } while(mdtmp);
125
126 BIO_free_all(bio);
127
128=head1 BUGS
129
130The lack of support for BIO_puts() and the non standard behaviour of
131BIO_gets() could be regarded as anomalous. It could be argued that BIO_gets()
132and BIO_puts() should be passed to the next BIO in the chain and digest
133the data passed through and that digests should be retrieved using a
134separate BIO_ctrl() call.
135
136=head1 SEE ALSO
137
138TBA
139