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135 .\" ========================================================================
136 .\"
137 .IX Title "BIO_f_md 3"
138 .TH BIO_f_md 3 "2009-12-26" "1.0.1n" "OpenSSL"
139 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
140 .\" way too many mistakes in technical documents.
141 .if n .ad l
142 .nh
143 .SH "NAME"
144 BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx \- message digest BIO filter
145 .SH "LIBRARY"
146 libcrypto, -lcrypto
147 .SH "SYNOPSIS"
148 .IX Header "SYNOPSIS"
149 .Vb 2
150 \& #include <openssl/bio.h>
151 \& #include <openssl/evp.h>
152 \&
153 \& BIO_METHOD * BIO_f_md(void);
154 \& int BIO_set_md(BIO *b,EVP_MD *md);
155 \& int BIO_get_md(BIO *b,EVP_MD **mdp);
156 \& int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp);
157 .Ve
158 .SH "DESCRIPTION"
159 .IX Header "DESCRIPTION"
160 \&\fIBIO_f_md()\fR returns the message digest \s-1BIO\s0 method. This is a filter
161 \&\s-1BIO\s0 that digests any data passed through it, it is a \s-1BIO\s0 wrapper
162 for the digest routines \fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR
163 and \fIEVP_DigestFinal()\fR.
164 .PP
165 Any data written or read through a digest \s-1BIO\s0 using \fIBIO_read()\fR and
166 \&\fIBIO_write()\fR is digested.
167 .PP
168 \&\fIBIO_gets()\fR, if its \fBsize\fR parameter is large enough finishes the
169 digest calculation and returns the digest value. \fIBIO_puts()\fR is
170 not supported.
171 .PP
172 \&\fIBIO_reset()\fR reinitialises a digest \s-1BIO.\s0
173 .PP
174 \&\fIBIO_set_md()\fR sets the message digest of \s-1BIO \s0\fBb\fR to \fBmd\fR: this
175 must be called to initialize a digest \s-1BIO\s0 before any data is
176 passed through it. It is a \fIBIO_ctrl()\fR macro.
177 .PP
178 \&\fIBIO_get_md()\fR places the a pointer to the digest BIOs digest method
179 in \fBmdp\fR, it is a \fIBIO_ctrl()\fR macro.
180 .PP
181 \&\fIBIO_get_md_ctx()\fR returns the digest BIOs context into \fBmdcp\fR.
182 .SH "NOTES"
183 .IX Header "NOTES"
184 The context returned by \fIBIO_get_md_ctx()\fR can be used in calls
185 to \fIEVP_DigestFinal()\fR and also the signature routines \fIEVP_SignFinal()\fR
186 and \fIEVP_VerifyFinal()\fR.
187 .PP
188 The context returned by \fIBIO_get_md_ctx()\fR is an internal context
189 structure. Changes made to this context will affect the digest
190 \&\s-1BIO\s0 itself and the context pointer will become invalid when the digest
191 \&\s-1BIO\s0 is freed.
192 .PP
193 After the digest has been retrieved from a digest \s-1BIO\s0 it must be
194 reinitialized by calling \fIBIO_reset()\fR, or \fIBIO_set_md()\fR before any more
195 data is passed through it.
196 .PP
197 If an application needs to call \fIBIO_gets()\fR or \fIBIO_puts()\fR through
198 a chain containing digest BIOs then this can be done by prepending
199 a buffering \s-1BIO.\s0
200 .PP
201 Before OpenSSL 1.0.0 the call to \fIBIO_get_md_ctx()\fR would only work if the \s-1BIO\s0
202 had been initialized for example by calling \fIBIO_set_md()\fR ). In OpenSSL
203 1.0.0 and later the context is always returned and the \s-1BIO\s0 is state is set
204 to initialized. This allows applications to initialize the context externally
205 if the standard calls such as \fIBIO_set_md()\fR are not sufficiently flexible.
206 .SH "RETURN VALUES"
207 .IX Header "RETURN VALUES"
208 \&\fIBIO_f_md()\fR returns the digest \s-1BIO\s0 method.
209 .PP
210 \&\fIBIO_set_md()\fR, \fIBIO_get_md()\fR and \fIBIO_md_ctx()\fR return 1 for success and
211 0 for failure.
212 .SH "EXAMPLES"
213 .IX Header "EXAMPLES"
214 The following example creates a \s-1BIO\s0 chain containing an \s-1SHA1\s0 and \s-1MD5\s0
215 digest \s-1BIO\s0 and passes the string \*(L"Hello World\*(R" through it. Error
216 checking has been omitted for clarity.
217 .PP
218 .Vb 10
219 \& BIO *bio, *mdtmp;
220 \& char message[] = "Hello World";
221 \& bio = BIO_new(BIO_s_null());
222 \& mdtmp = BIO_new(BIO_f_md());
223 \& BIO_set_md(mdtmp, EVP_sha1());
224 \& /* For BIO_push() we want to append the sink BIO and keep a note of
225 \& * the start of the chain.
226 \& */
227 \& bio = BIO_push(mdtmp, bio);
228 \& mdtmp = BIO_new(BIO_f_md());
229 \& BIO_set_md(mdtmp, EVP_md5());
230 \& bio = BIO_push(mdtmp, bio);
231 \& /* Note: mdtmp can now be discarded */
232 \& BIO_write(bio, message, strlen(message));
233 .Ve
234 .PP
235 The next example digests data by reading through a chain instead:
236 .PP
237 .Vb 10
238 \& BIO *bio, *mdtmp;
239 \& char buf[1024];
240 \& int rdlen;
241 \& bio = BIO_new_file(file, "rb");
242 \& mdtmp = BIO_new(BIO_f_md());
243 \& BIO_set_md(mdtmp, EVP_sha1());
244 \& bio = BIO_push(mdtmp, bio);
245 \& mdtmp = BIO_new(BIO_f_md());
246 \& BIO_set_md(mdtmp, EVP_md5());
247 \& bio = BIO_push(mdtmp, bio);
248 \& do {
249 \& rdlen = BIO_read(bio, buf, sizeof(buf));
250 \& /* Might want to do something with the data here */
251 \& } while(rdlen > 0);
252 .Ve
253 .PP
254 This next example retrieves the message digests from a \s-1BIO\s0 chain and
255 outputs them. This could be used with the examples above.
256 .PP
257 .Vb 10
258 \& BIO *mdtmp;
259 \& unsigned char mdbuf[EVP_MAX_MD_SIZE];
260 \& int mdlen;
261 \& int i;
262 \& mdtmp = bio; /* Assume bio has previously been set up */
263 \& do {
264 \& EVP_MD *md;
265 \& mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
266 \& if(!mdtmp) break;
267 \& BIO_get_md(mdtmp, &md);
268 \& printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));
269 \& mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
270 \& for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);
271 \& printf("\en");
272 \& mdtmp = BIO_next(mdtmp);
273 \& } while(mdtmp);
274 \&
275 \& BIO_free_all(bio);
276 .Ve
277 .SH "BUGS"
278 .IX Header "BUGS"
279 The lack of support for \fIBIO_puts()\fR and the non standard behaviour of
280 \&\fIBIO_gets()\fR could be regarded as anomalous. It could be argued that \fIBIO_gets()\fR
281 and \fIBIO_puts()\fR should be passed to the next \s-1BIO\s0 in the chain and digest
282 the data passed through and that digests should be retrieved using a
283 separate \fIBIO_ctrl()\fR call.
284 .SH "SEE ALSO"
285 .IX Header "SEE ALSO"
286 \&\s-1TBA\s0