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131 .IX Title "BIO_f_md 3"
132 .TH BIO_f_md 3 "2018-03-27" "1.0.2o" "OpenSSL"
133 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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138 BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx \- message digest BIO filter
140 .IX Header "SYNOPSIS"
142 \& #include <openssl/bio.h>
143 \& #include <openssl/evp.h>
145 \& BIO_METHOD * BIO_f_md(void);
146 \& int BIO_set_md(BIO *b,EVP_MD *md);
147 \& int BIO_get_md(BIO *b,EVP_MD **mdp);
148 \& int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp);
151 .IX Header "DESCRIPTION"
152 \&\fIBIO_f_md()\fR returns the message digest \s-1BIO\s0 method. This is a filter
153 \&\s-1BIO\s0 that digests any data passed through it, it is a \s-1BIO\s0 wrapper
154 for the digest routines \fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR
155 and \fIEVP_DigestFinal()\fR.
157 Any data written or read through a digest \s-1BIO\s0 using \fIBIO_read()\fR and
158 \&\fIBIO_write()\fR is digested.
160 \&\fIBIO_gets()\fR, if its \fBsize\fR parameter is large enough finishes the
161 digest calculation and returns the digest value. \fIBIO_puts()\fR is
164 \&\fIBIO_reset()\fR reinitialises a digest \s-1BIO.\s0
166 \&\fIBIO_set_md()\fR sets the message digest of \s-1BIO \s0\fBb\fR to \fBmd\fR: this
167 must be called to initialize a digest \s-1BIO\s0 before any data is
168 passed through it. It is a \fIBIO_ctrl()\fR macro.
170 \&\fIBIO_get_md()\fR places the a pointer to the digest BIOs digest method
171 in \fBmdp\fR, it is a \fIBIO_ctrl()\fR macro.
173 \&\fIBIO_get_md_ctx()\fR returns the digest BIOs context into \fBmdcp\fR.
176 The context returned by \fIBIO_get_md_ctx()\fR can be used in calls
177 to \fIEVP_DigestFinal()\fR and also the signature routines \fIEVP_SignFinal()\fR
178 and \fIEVP_VerifyFinal()\fR.
180 The context returned by \fIBIO_get_md_ctx()\fR is an internal context
181 structure. Changes made to this context will affect the digest
182 \&\s-1BIO\s0 itself and the context pointer will become invalid when the digest
183 \&\s-1BIO\s0 is freed.
185 After the digest has been retrieved from a digest \s-1BIO\s0 it must be
186 reinitialized by calling \fIBIO_reset()\fR, or \fIBIO_set_md()\fR before any more
187 data is passed through it.
189 If an application needs to call \fIBIO_gets()\fR or \fIBIO_puts()\fR through
190 a chain containing digest BIOs then this can be done by prepending
191 a buffering \s-1BIO.\s0
193 Before OpenSSL 1.0.0 the call to \fIBIO_get_md_ctx()\fR would only work if the \s-1BIO\s0
194 had been initialized for example by calling \fIBIO_set_md()\fR ). In OpenSSL
195 1.0.0 and later the context is always returned and the \s-1BIO\s0 is state is set
196 to initialized. This allows applications to initialize the context externally
197 if the standard calls such as \fIBIO_set_md()\fR are not sufficiently flexible.
199 .IX Header "RETURN VALUES"
200 \&\fIBIO_f_md()\fR returns the digest \s-1BIO\s0 method.
202 \&\fIBIO_set_md()\fR, \fIBIO_get_md()\fR and \fIBIO_md_ctx()\fR return 1 for success and
205 .IX Header "EXAMPLES"
206 The following example creates a \s-1BIO\s0 chain containing an \s-1SHA1\s0 and \s-1MD5\s0
207 digest \s-1BIO\s0 and passes the string \*(L"Hello World\*(R" through it. Error
208 checking has been omitted for clarity.
212 \& char message[] = "Hello World";
213 \& bio = BIO_new(BIO_s_null());
214 \& mdtmp = BIO_new(BIO_f_md());
215 \& BIO_set_md(mdtmp, EVP_sha1());
216 \& /* For BIO_push() we want to append the sink BIO and keep a note of
217 \& * the start of the chain.
219 \& bio = BIO_push(mdtmp, bio);
220 \& mdtmp = BIO_new(BIO_f_md());
221 \& BIO_set_md(mdtmp, EVP_md5());
222 \& bio = BIO_push(mdtmp, bio);
223 \& /* Note: mdtmp can now be discarded */
224 \& BIO_write(bio, message, strlen(message));
227 The next example digests data by reading through a chain instead:
233 \& bio = BIO_new_file(file, "rb");
234 \& mdtmp = BIO_new(BIO_f_md());
235 \& BIO_set_md(mdtmp, EVP_sha1());
236 \& bio = BIO_push(mdtmp, bio);
237 \& mdtmp = BIO_new(BIO_f_md());
238 \& BIO_set_md(mdtmp, EVP_md5());
239 \& bio = BIO_push(mdtmp, bio);
241 \& rdlen = BIO_read(bio, buf, sizeof(buf));
242 \& /* Might want to do something with the data here */
243 \& } while(rdlen > 0);
246 This next example retrieves the message digests from a \s-1BIO\s0 chain and
247 outputs them. This could be used with the examples above.
251 \& unsigned char mdbuf[EVP_MAX_MD_SIZE];
254 \& mdtmp = bio; /* Assume bio has previously been set up */
257 \& mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
259 \& BIO_get_md(mdtmp, &md);
260 \& printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));
261 \& mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
262 \& for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);
264 \& mdtmp = BIO_next(mdtmp);
267 \& BIO_free_all(bio);
271 The lack of support for \fIBIO_puts()\fR and the non standard behaviour of
272 \&\fIBIO_gets()\fR could be regarded as anomalous. It could be argued that \fIBIO_gets()\fR
273 and \fIBIO_puts()\fR should be passed to the next \s-1BIO\s0 in the chain and digest
274 the data passed through and that digests should be retrieved using a
275 separate \fIBIO_ctrl()\fR call.
277 .IX Header "SEE ALSO"