5 BIO_f_md - message digest BIO
9 #include <openssl/bio.h>
10 #include <openssl/evp.h>
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);
19 BIO_f_md() returns the message digest BIO method. This is a filter
20 BIO that digests any data passed through it, it is a BIO wrapper
21 for the digest routines EVP_DigestInit(), EVP_DigestUpdate()
22 and EVP_DigestFinal().
24 Any data written or read through a digest BIO using BIO_read() and
25 BIO_write() is digested.
27 BIO_gets(), if its B<size> parameter is large enough finishes the
28 digest calculation and returns the digest value. BIO_puts() is
31 BIO_reset() reinitializes a digest BIO.
33 BIO_set_md() sets the message digest of BIO B<b> to B<md>: this
34 must be called to initialise a digest BIO before any data is
35 passed through it. It is a BIO_ctrl() macro.
37 BIO_get_md() places the a pointer to the digest BIOs digest method
38 in B<mdp>, it is a BIO_ctrl() macro.
40 BIO_get_md_ctx() returns the digest BIOs context into B<mdcp>.
44 The context returned by BIO_get_md_ctx() can be used in calls
45 to EVP_DigestFinal() and also the signature routines EVP_SignFinal()
46 and EVP_VerifyFinal().
48 The context returned by BIO_get_md_ctx() is an internal context
49 structure. Changes made to this context will affect the digest
50 BIO itself and the context pointer will become invalid when the digest
53 After the digest has been retrieved from a digest BIO it must be
54 reinitialized by calling BIO_reset(), or BIO_set_md() before any more
55 data is passed through it.
57 If an application needs to call BIO_gets() or BIO_puts() through
58 a chain containing digest BIOs then this can be done by prepending
63 BIO_f_md() returns the digest BIO method.
65 BIO_set_md(), BIO_get_md() and BIO_md_ctx() return 1 for success and
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.
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.
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));
89 The next example digests data by reading through a chain instead:
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);
102 rdlen = BIO_read(bio, buf, sizeof(buf));
103 /* Might want to do something with the data here */
106 This next example retrieves the message digests from a BIO chain and
107 outputs them. This could be used with the examples above.
110 unsigned char mdbuf[EVP_MAX_MD_SIZE];
113 mdtmp = bio; /* Assume bio has previously been set up */
116 mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
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]);
123 mdtmp = BIO_next(mdtmp);
130 The lack of support for BIO_puts() and the non standard behaviour of
131 BIO_gets() could be regarded as anomalous. It could be argued that BIO_gets()
132 and BIO_puts() should be passed to the next BIO in the chain and digest
133 the data passed through and that digests should be retrieved using a
134 separate BIO_ctrl() call.