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136 .IX Title "BIO_f_md 3"
137 .TH BIO_f_md 3 "2006-07-12" "1.1.0-dev" "OpenSSL"
138 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
139 .\" way too many mistakes in technical documents.
140 .if n .ad l
141 .nh
142 .SH "NAME"
143 BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx \- message digest BIO filter
144 .SH "LIBRARY"
145 libcrypto, -lcrypto
146 .SH "SYNOPSIS"
147 .IX Header "SYNOPSIS"
148 .Vb 2
149 \& #include <openssl/bio.h>
150 \& #include <openssl/evp.h>
151 \&
152 \& BIO_METHOD * BIO_f_md(void);
153 \& int BIO_set_md(BIO *b,EVP_MD *md);
154 \& int BIO_get_md(BIO *b,EVP_MD **mdp);
155 \& int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp);
156 .Ve
157 .SH "DESCRIPTION"
158 .IX Header "DESCRIPTION"
159 \&\fIBIO_f_md()\fR returns the message digest \s-1BIO\s0 method. This is a filter
160 \&\s-1BIO\s0 that digests any data passed through it, it is a \s-1BIO\s0 wrapper
161 for the digest routines \fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR
162 and \fIEVP_DigestFinal()\fR.
163 .PP
164 Any data written or read through a digest \s-1BIO\s0 using \fIBIO_read()\fR and
165 \&\fIBIO_write()\fR is digested.
166 .PP
167 \&\fIBIO_gets()\fR, if its \fBsize\fR parameter is large enough finishes the
168 digest calculation and returns the digest value. \fIBIO_puts()\fR is
169 not supported.
170 .PP
171 \&\fIBIO_reset()\fR reinitialises a digest \s-1BIO\s0.
172 .PP
173 \&\fIBIO_set_md()\fR sets the message digest of \s-1BIO\s0 \fBb\fR to \fBmd\fR: this
174 must be called to initialize a digest \s-1BIO\s0 before any data is
175 passed through it. It is a \fIBIO_ctrl()\fR macro.
176 .PP
177 \&\fIBIO_get_md()\fR places the a pointer to the digest BIOs digest method
178 in \fBmdp\fR, it is a \fIBIO_ctrl()\fR macro.
179 .PP
180 \&\fIBIO_get_md_ctx()\fR returns the digest BIOs context into \fBmdcp\fR.
181 .SH "NOTES"
182 .IX Header "NOTES"
183 The context returned by \fIBIO_get_md_ctx()\fR can be used in calls
184 to \fIEVP_DigestFinal()\fR and also the signature routines \fIEVP_SignFinal()\fR
185 and \fIEVP_VerifyFinal()\fR.
186 .PP
187 The context returned by \fIBIO_get_md_ctx()\fR is an internal context
188 structure. Changes made to this context will affect the digest
189 \&\s-1BIO\s0 itself and the context pointer will become invalid when the digest
190 \&\s-1BIO\s0 is freed.
191 .PP
192 After the digest has been retrieved from a digest \s-1BIO\s0 it must be
193 reinitialized by calling \fIBIO_reset()\fR, or \fIBIO_set_md()\fR before any more
194 data is passed through it.
195 .PP
196 If an application needs to call \fIBIO_gets()\fR or \fIBIO_puts()\fR through
197 a chain containing digest BIOs then this can be done by prepending
198 a buffering \s-1BIO\s0.
199 .PP
200 Before OpenSSL 0.9.9 the call to \fIBIO_get_md_ctx()\fR would only work if the \s-1BIO\s0
201 had been initialized for example by calling \fIBIO_set_md()\fR ). In OpenSSL
202 0.9.9 and later the context is always returned and the \s-1BIO\s0 is state is set
203 to initialized. This allows applications to initialize the context externally
204 if the standard calls such as \fIBIO_set_md()\fR are not sufficiently flexible.
205 .SH "RETURN VALUES"
206 .IX Header "RETURN VALUES"
207 \&\fIBIO_f_md()\fR returns the digest \s-1BIO\s0 method.
208 .PP
209 \&\fIBIO_set_md()\fR, \fIBIO_get_md()\fR and \fIBIO_md_ctx()\fR return 1 for success and
210 0 for failure.
211 .SH "EXAMPLES"
212 .IX Header "EXAMPLES"
213 The following example creates a \s-1BIO\s0 chain containing an \s-1SHA1\s0 and \s-1MD5\s0
214 digest \s-1BIO\s0 and passes the string \*(L"Hello World\*(R" through it. Error
215 checking has been omitted for clarity.
216 .PP
217 .Vb 10
218 \& BIO *bio, *mdtmp;
219 \& char message[] = "Hello World";
220 \& bio = BIO_new(BIO_s_null());
221 \& mdtmp = BIO_new(BIO_f_md());
222 \& BIO_set_md(mdtmp, EVP_sha1());
223 \& /* For BIO_push() we want to append the sink BIO and keep a note of
224 \& * the start of the chain.
225 \& */
226 \& bio = BIO_push(mdtmp, bio);
227 \& mdtmp = BIO_new(BIO_f_md());
228 \& BIO_set_md(mdtmp, EVP_md5());
229 \& bio = BIO_push(mdtmp, bio);
230 \& /* Note: mdtmp can now be discarded */
231 \& BIO_write(bio, message, strlen(message));
232 .Ve
233 .PP
234 The next example digests data by reading through a chain instead:
235 .PP
236 .Vb 10
237 \& BIO *bio, *mdtmp;
238 \& char buf[1024];
239 \& int rdlen;
240 \& bio = BIO_new_file(file, "rb");
241 \& mdtmp = BIO_new(BIO_f_md());
242 \& BIO_set_md(mdtmp, EVP_sha1());
243 \& bio = BIO_push(mdtmp, bio);
244 \& mdtmp = BIO_new(BIO_f_md());
245 \& BIO_set_md(mdtmp, EVP_md5());
246 \& bio = BIO_push(mdtmp, bio);
247 \& do {
248 \& rdlen = BIO_read(bio, buf, sizeof(buf));
249 \& /* Might want to do something with the data here */
250 \& } while(rdlen > 0);
251 .Ve
252 .PP
253 This next example retrieves the message digests from a \s-1BIO\s0 chain and
254 outputs them. This could be used with the examples above.
255 .PP
256 .Vb 10
257 \& BIO *mdtmp;
258 \& unsigned char mdbuf[EVP_MAX_MD_SIZE];
259 \& int mdlen;
260 \& int i;
261 \& mdtmp = bio; /* Assume bio has previously been set up */
262 \& do {
263 \& EVP_MD *md;
264 \& mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
265 \& if(!mdtmp) break;
266 \& BIO_get_md(mdtmp, &md);
267 \& printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));
268 \& mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
269 \& for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);
270 \& printf("\en");
271 \& mdtmp = BIO_next(mdtmp);
272 \& } while(mdtmp);
273 \&
274 \& BIO_free_all(bio);
275 .Ve
276 .SH "BUGS"
277 .IX Header "BUGS"
278 The lack of support for \fIBIO_puts()\fR and the non standard behaviour of
279 \&\fIBIO_gets()\fR could be regarded as anomalous. It could be argued that \fIBIO_gets()\fR
280 and \fIBIO_puts()\fR should be passed to the next \s-1BIO\s0 in the chain and digest
281 the data passed through and that digests should be retrieved using a
282 separate \fIBIO_ctrl()\fR call.
283 .SH "SEE ALSO"
284 .IX Header "SEE ALSO"
285 \&\s-1TBA\s0