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140 .IX Title "BIO_f_md 3"
141 .TH BIO_f_md 3 "0.9.7a" "2003-02-19" "OpenSSL"
144 BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx \- message digest \s-1BIO\s0 filter
146 .IX Header "SYNOPSIS"
148 \& #include <openssl/bio.h>
149 \& #include <openssl/evp.h>
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);
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.
164 Any data written or read through a digest \s-1BIO\s0 using \fIBIO_read()\fR and
165 \&\fIBIO_write()\fR is digested.
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
171 \&\fIBIO_reset()\fR reinitialises a digest \s-1BIO\s0.
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.
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.
180 \&\fIBIO_get_md_ctx()\fR returns the digest BIOs context into \fBmdcp\fR.
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.
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.
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.
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.
200 .IX Header "RETURN VALUES"
201 \&\fIBIO_f_md()\fR returns the digest \s-1BIO\s0 method.
203 \&\fIBIO_set_md()\fR, \fIBIO_get_md()\fR and \fIBIO_md_ctx()\fR return 1 for success and
206 .IX Header "EXAMPLES"
207 The following example creates a \s-1BIO\s0 chain containing an \s-1SHA1\s0 and \s-1MD5\s0
208 digest \s-1BIO\s0 and passes the string \*(L"Hello World\*(R" through it. Error
209 checking has been omitted for clarity.
213 \& char message[] = "Hello World";
214 \& bio = BIO_new(BIO_s_null());
215 \& mdtmp = BIO_new(BIO_f_md());
216 \& BIO_set_md(mdtmp, EVP_sha1());
217 \& /* For BIO_push() we want to append the sink BIO and keep a note of
218 \& * the start of the chain.
220 \& bio = BIO_push(mdtmp, bio);
221 \& mdtmp = BIO_new(BIO_f_md());
222 \& BIO_set_md(mdtmp, EVP_md5());
223 \& bio = BIO_push(mdtmp, bio);
224 \& /* Note: mdtmp can now be discarded */
225 \& 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);
245 This next example retrieves the message digests from a \s-1BIO\s0 chain and
246 outputs them. This could be used with the examples above.
250 \& unsigned char mdbuf[EVP_MAX_MD_SIZE];
253 \& mdtmp = bio; /* Assume bio has previously been set up */
256 \& mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
258 \& BIO_get_md(mdtmp, &md);
259 \& printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));
260 \& mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
261 \& for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);
263 \& 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"