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133 .\" ========================================================================
135 .IX Title "BIO_F_MD 3"
136 .TH BIO_F_MD 3 "2020-12-08" "1.1.1i" "OpenSSL"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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142 BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx \- message digest BIO filter
144 .IX Header "SYNOPSIS"
146 \& #include <openssl/bio.h>
147 \& #include <openssl/evp.h>
149 \& const 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);
155 .IX Header "DESCRIPTION"
156 \&\fBBIO_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 \fBEVP_DigestInit()\fR, \fBEVP_DigestUpdate()\fR
159 and \fBEVP_DigestFinal()\fR.
161 Any data written or read through a digest \s-1BIO\s0 using \fBBIO_read_ex()\fR and
162 \&\fBBIO_write_ex()\fR is digested.
164 \&\fBBIO_gets()\fR, if its \fBsize\fR parameter is large enough finishes the
165 digest calculation and returns the digest value. \fBBIO_puts()\fR is
168 \&\fBBIO_reset()\fR reinitialises a digest \s-1BIO.\s0
170 \&\fBBIO_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 \fBBIO_ctrl()\fR macro.
174 \&\fBBIO_get_md()\fR places the a pointer to the digest BIOs digest method
175 in \fBmdp\fR, it is a \fBBIO_ctrl()\fR macro.
177 \&\fBBIO_get_md_ctx()\fR returns the digest BIOs context into \fBmdcp\fR.
180 The context returned by \fBBIO_get_md_ctx()\fR can be used in calls
181 to \fBEVP_DigestFinal()\fR and also the signature routines \fBEVP_SignFinal()\fR
182 and \fBEVP_VerifyFinal()\fR.
184 The context returned by \fBBIO_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.
189 After the digest has been retrieved from a digest \s-1BIO\s0 it must be
190 reinitialized by calling \fBBIO_reset()\fR, or \fBBIO_set_md()\fR before any more
191 data is passed through it.
193 If an application needs to call \fBBIO_gets()\fR or \fBBIO_puts()\fR through
194 a chain containing digest BIOs then this can be done by prepending
195 a buffering \s-1BIO.\s0
197 Calling \fBBIO_get_md_ctx()\fR will return the context and initialize the \s-1BIO\s0
198 state. This allows applications to initialize the context externally
199 if the standard calls such as \fBBIO_set_md()\fR are not sufficiently flexible.
201 .IX Header "RETURN VALUES"
202 \&\fBBIO_f_md()\fR returns the digest \s-1BIO\s0 method.
204 \&\fBBIO_set_md()\fR, \fBBIO_get_md()\fR and \fBBIO_md_ctx()\fR return 1 for success and
207 .IX Header "EXAMPLES"
208 The following example creates a \s-1BIO\s0 chain containing an \s-1SHA1\s0 and \s-1MD5\s0
209 digest \s-1BIO\s0 and passes the string \*(L"Hello World\*(R" through it. Error
210 checking has been omitted for clarity.
214 \& char message[] = "Hello World";
216 \& bio = BIO_new(BIO_s_null());
217 \& mdtmp = BIO_new(BIO_f_md());
218 \& 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.
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));
231 The next example digests data by reading through a chain instead:
238 \& bio = BIO_new_file(file, "rb");
239 \& mdtmp = BIO_new(BIO_f_md());
240 \& BIO_set_md(mdtmp, EVP_sha1());
241 \& bio = BIO_push(mdtmp, bio);
242 \& mdtmp = BIO_new(BIO_f_md());
243 \& BIO_set_md(mdtmp, EVP_md5());
244 \& bio = BIO_push(mdtmp, bio);
246 \& rdlen = BIO_read(bio, buf, sizeof(buf));
247 \& /* Might want to do something with the data here */
248 \& } while (rdlen > 0);
251 This next example retrieves the message digests from a \s-1BIO\s0 chain and
252 outputs them. This could be used with the examples above.
256 \& unsigned char mdbuf[EVP_MAX_MD_SIZE];
260 \& mdtmp = bio; /* Assume bio has previously been set up */
264 \& mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
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]);
272 \& mdtmp = BIO_next(mdtmp);
275 \& BIO_free_all(bio);
279 The lack of support for \fBBIO_puts()\fR and the non standard behaviour of
280 \&\fBBIO_gets()\fR could be regarded as anomalous. It could be argued that \fBBIO_gets()\fR
281 and \fBBIO_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 \fBBIO_ctrl()\fR call.
286 Before OpenSSL 1.0.0., the call to \fBBIO_get_md_ctx()\fR would only work if the
287 \&\s-1BIO\s0 was initialized first.
289 .IX Header "COPYRIGHT"
290 Copyright 2000\-2016 The OpenSSL Project Authors. All Rights Reserved.
292 Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use
293 this file except in compliance with the License. You can obtain a copy
294 in the file \s-1LICENSE\s0 in the source distribution or at
295 <https://www.openssl.org/source/license.html>.