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129 .\" ========================================================================
131 .IX Title "BIO_f_md 3"
132 .TH BIO_f_md 3 "2008-09-27" "0.9.8i" "OpenSSL"
134 BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx \- message digest BIO filter
136 .IX Header "SYNOPSIS"
138 \& #include <openssl/bio.h>
139 \& #include <openssl/evp.h>
143 \& BIO_METHOD * BIO_f_md(void);
144 \& int BIO_set_md(BIO *b,EVP_MD *md);
145 \& int BIO_get_md(BIO *b,EVP_MD **mdp);
146 \& int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp);
149 .IX Header "DESCRIPTION"
150 \&\fIBIO_f_md()\fR returns the message digest \s-1BIO\s0 method. This is a filter
151 \&\s-1BIO\s0 that digests any data passed through it, it is a \s-1BIO\s0 wrapper
152 for the digest routines \fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR
153 and \fIEVP_DigestFinal()\fR.
155 Any data written or read through a digest \s-1BIO\s0 using \fIBIO_read()\fR and
156 \&\fIBIO_write()\fR is digested.
158 \&\fIBIO_gets()\fR, if its \fBsize\fR parameter is large enough finishes the
159 digest calculation and returns the digest value. \fIBIO_puts()\fR is
162 \&\fIBIO_reset()\fR reinitialises a digest \s-1BIO\s0.
164 \&\fIBIO_set_md()\fR sets the message digest of \s-1BIO\s0 \fBb\fR to \fBmd\fR: this
165 must be called to initialize a digest \s-1BIO\s0 before any data is
166 passed through it. It is a \fIBIO_ctrl()\fR macro.
168 \&\fIBIO_get_md()\fR places the a pointer to the digest BIOs digest method
169 in \fBmdp\fR, it is a \fIBIO_ctrl()\fR macro.
171 \&\fIBIO_get_md_ctx()\fR returns the digest BIOs context into \fBmdcp\fR.
174 The context returned by \fIBIO_get_md_ctx()\fR can be used in calls
175 to \fIEVP_DigestFinal()\fR and also the signature routines \fIEVP_SignFinal()\fR
176 and \fIEVP_VerifyFinal()\fR.
178 The context returned by \fIBIO_get_md_ctx()\fR is an internal context
179 structure. Changes made to this context will affect the digest
180 \&\s-1BIO\s0 itself and the context pointer will become invalid when the digest
181 \&\s-1BIO\s0 is freed.
183 After the digest has been retrieved from a digest \s-1BIO\s0 it must be
184 reinitialized by calling \fIBIO_reset()\fR, or \fIBIO_set_md()\fR before any more
185 data is passed through it.
187 If an application needs to call \fIBIO_gets()\fR or \fIBIO_puts()\fR through
188 a chain containing digest BIOs then this can be done by prepending
189 a buffering \s-1BIO\s0.
191 .IX Header "RETURN VALUES"
192 \&\fIBIO_f_md()\fR returns the digest \s-1BIO\s0 method.
194 \&\fIBIO_set_md()\fR, \fIBIO_get_md()\fR and \fIBIO_md_ctx()\fR return 1 for success and
197 .IX Header "EXAMPLES"
198 The following example creates a \s-1BIO\s0 chain containing an \s-1SHA1\s0 and \s-1MD5\s0
199 digest \s-1BIO\s0 and passes the string \*(L"Hello World\*(R" through it. Error
200 checking has been omitted for clarity.
204 \& char message[] = "Hello World";
205 \& bio = BIO_new(BIO_s_null());
206 \& mdtmp = BIO_new(BIO_f_md());
207 \& BIO_set_md(mdtmp, EVP_sha1());
208 \& /* For BIO_push() we want to append the sink BIO and keep a note of
209 \& * the start of the chain.
211 \& bio = BIO_push(mdtmp, bio);
212 \& mdtmp = BIO_new(BIO_f_md());
213 \& BIO_set_md(mdtmp, EVP_md5());
214 \& bio = BIO_push(mdtmp, bio);
215 \& /* Note: mdtmp can now be discarded */
216 \& BIO_write(bio, message, strlen(message));
219 The next example digests data by reading through a chain instead:
225 \& bio = BIO_new_file(file, "rb");
226 \& mdtmp = BIO_new(BIO_f_md());
227 \& BIO_set_md(mdtmp, EVP_sha1());
228 \& bio = BIO_push(mdtmp, bio);
229 \& mdtmp = BIO_new(BIO_f_md());
230 \& BIO_set_md(mdtmp, EVP_md5());
231 \& bio = BIO_push(mdtmp, bio);
233 \& rdlen = BIO_read(bio, buf, sizeof(buf));
234 \& /* Might want to do something with the data here */
235 \& } while(rdlen > 0);
238 This next example retrieves the message digests from a \s-1BIO\s0 chain and
239 outputs them. This could be used with the examples above.
243 \& unsigned char mdbuf[EVP_MAX_MD_SIZE];
246 \& mdtmp = bio; /* Assume bio has previously been set up */
249 \& mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
251 \& BIO_get_md(mdtmp, &md);
252 \& printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));
253 \& mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
254 \& for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);
256 \& mdtmp = BIO_next(mdtmp);
261 \& BIO_free_all(bio);
265 The lack of support for \fIBIO_puts()\fR and the non standard behaviour of
266 \&\fIBIO_gets()\fR could be regarded as anomalous. It could be argued that \fIBIO_gets()\fR
267 and \fIBIO_puts()\fR should be passed to the next \s-1BIO\s0 in the chain and digest
268 the data passed through and that digests should be retrieved using a
269 separate \fIBIO_ctrl()\fR call.
271 .IX Header "SEE ALSO"