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135 .IX Title "BIO_f_md 3"
136 .TH BIO_f_md 3 "2016-05-03" "1.0.2h" "OpenSSL"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
138 .\" way too many mistakes in technical documents.
139 .if n .ad l
140 .nh
141 .SH "NAME"
142 BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx \- message digest BIO filter
143 .SH "SYNOPSIS"
144 .IX Header "SYNOPSIS"
145 .Vb 2
146 \& #include <openssl/bio.h>
147 \& #include <openssl/evp.h>
148 \&
149 \& BIO_METHOD * BIO_f_md(void);
150 \& int BIO_set_md(BIO *b,EVP_MD *md);
151 \& int BIO_get_md(BIO *b,EVP_MD **mdp);
152 \& int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp);
153 .Ve
154 .SH "DESCRIPTION"
155 .IX Header "DESCRIPTION"
156 \&\fIBIO_f_md()\fR returns the message digest \s-1BIO\s0 method. This is a filter
157 \&\s-1BIO\s0 that digests any data passed through it, it is a \s-1BIO\s0 wrapper
158 for the digest routines \fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR
159 and \fIEVP_DigestFinal()\fR.
160 .PP
161 Any data written or read through a digest \s-1BIO\s0 using \fIBIO_read()\fR and
162 \&\fIBIO_write()\fR is digested.
163 .PP
164 \&\fIBIO_gets()\fR, if its \fBsize\fR parameter is large enough finishes the
165 digest calculation and returns the digest value. \fIBIO_puts()\fR is
166 not supported.
167 .PP
168 \&\fIBIO_reset()\fR reinitialises a digest \s-1BIO.\s0
169 .PP
170 \&\fIBIO_set_md()\fR sets the message digest of \s-1BIO \s0\fBb\fR to \fBmd\fR: this
171 must be called to initialize a digest \s-1BIO\s0 before any data is
172 passed through it. It is a \fIBIO_ctrl()\fR macro.
173 .PP
174 \&\fIBIO_get_md()\fR places the a pointer to the digest BIOs digest method
175 in \fBmdp\fR, it is a \fIBIO_ctrl()\fR macro.
176 .PP
177 \&\fIBIO_get_md_ctx()\fR returns the digest BIOs context into \fBmdcp\fR.
178 .SH "NOTES"
179 .IX Header "NOTES"
180 The context returned by \fIBIO_get_md_ctx()\fR can be used in calls
181 to \fIEVP_DigestFinal()\fR and also the signature routines \fIEVP_SignFinal()\fR
182 and \fIEVP_VerifyFinal()\fR.
183 .PP
184 The context returned by \fIBIO_get_md_ctx()\fR is an internal context
185 structure. Changes made to this context will affect the digest
186 \&\s-1BIO\s0 itself and the context pointer will become invalid when the digest
187 \&\s-1BIO\s0 is freed.
188 .PP
189 After the digest has been retrieved from a digest \s-1BIO\s0 it must be
190 reinitialized by calling \fIBIO_reset()\fR, or \fIBIO_set_md()\fR before any more
191 data is passed through it.
192 .PP
193 If an application needs to call \fIBIO_gets()\fR or \fIBIO_puts()\fR through
194 a chain containing digest BIOs then this can be done by prepending
195 a buffering \s-1BIO.\s0
196 .PP
197 Before OpenSSL 1.0.0 the call to \fIBIO_get_md_ctx()\fR would only work if the \s-1BIO\s0
198 had been initialized for example by calling \fIBIO_set_md()\fR ). In OpenSSL
199 1.0.0 and later the context is always returned and the \s-1BIO\s0 is state is set
200 to initialized. This allows applications to initialize the context externally
201 if the standard calls such as \fIBIO_set_md()\fR are not sufficiently flexible.
202 .SH "RETURN VALUES"
203 .IX Header "RETURN VALUES"
204 \&\fIBIO_f_md()\fR returns the digest \s-1BIO\s0 method.
205 .PP
206 \&\fIBIO_set_md()\fR, \fIBIO_get_md()\fR and \fIBIO_md_ctx()\fR return 1 for success and
207 0 for failure.
208 .SH "EXAMPLES"
209 .IX Header "EXAMPLES"
210 The following example creates a \s-1BIO\s0 chain containing an \s-1SHA1\s0 and \s-1MD5\s0
211 digest \s-1BIO\s0 and passes the string \*(L"Hello World\*(R" through it. Error
212 checking has been omitted for clarity.
213 .PP
214 .Vb 10
215 \& BIO *bio, *mdtmp;
216 \& char message[] = "Hello World";
217 \& bio = BIO_new(BIO_s_null());
218 \& mdtmp = BIO_new(BIO_f_md());
219 \& BIO_set_md(mdtmp, EVP_sha1());
220 \& /* For BIO_push() we want to append the sink BIO and keep a note of
221 \& * the start of the chain.
222 \& */
223 \& bio = BIO_push(mdtmp, bio);
224 \& mdtmp = BIO_new(BIO_f_md());
225 \& BIO_set_md(mdtmp, EVP_md5());
226 \& bio = BIO_push(mdtmp, bio);
227 \& /* Note: mdtmp can now be discarded */
228 \& BIO_write(bio, message, strlen(message));
229 .Ve
230 .PP
231 The next example digests data by reading through a chain instead:
232 .PP
233 .Vb 10
234 \& BIO *bio, *mdtmp;
235 \& char buf[1024];
236 \& int rdlen;
237 \& bio = BIO_new_file(file, "rb");
238 \& mdtmp = BIO_new(BIO_f_md());
239 \& BIO_set_md(mdtmp, EVP_sha1());
240 \& bio = BIO_push(mdtmp, bio);
241 \& mdtmp = BIO_new(BIO_f_md());
242 \& BIO_set_md(mdtmp, EVP_md5());
243 \& bio = BIO_push(mdtmp, bio);
244 \& do {
245 \& rdlen = BIO_read(bio, buf, sizeof(buf));
246 \& /* Might want to do something with the data here */
247 \& } while(rdlen > 0);
248 .Ve
249 .PP
250 This next example retrieves the message digests from a \s-1BIO\s0 chain and
251 outputs them. This could be used with the examples above.
252 .PP
253 .Vb 10
254 \& BIO *mdtmp;
255 \& unsigned char mdbuf[EVP_MAX_MD_SIZE];
256 \& int mdlen;
257 \& int i;
258 \& mdtmp = bio; /* Assume bio has previously been set up */
259 \& do {
260 \& EVP_MD *md;
261 \& mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
262 \& if(!mdtmp) break;
263 \& BIO_get_md(mdtmp, &md);
264 \& printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));
265 \& mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
266 \& for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);
267 \& printf("\en");
268 \& mdtmp = BIO_next(mdtmp);
269 \& } while(mdtmp);
270 \&
271 \& BIO_free_all(bio);
272 .Ve
273 .SH "BUGS"
274 .IX Header "BUGS"
275 The lack of support for \fIBIO_puts()\fR and the non standard behaviour of
276 \&\fIBIO_gets()\fR could be regarded as anomalous. It could be argued that \fIBIO_gets()\fR
277 and \fIBIO_puts()\fR should be passed to the next \s-1BIO\s0 in the chain and digest
278 the data passed through and that digests should be retrieved using a
279 separate \fIBIO_ctrl()\fR call.
280 .SH "SEE ALSO"
281 .IX Header "SEE ALSO"
282 \&\s-1TBA\s0