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129.\" ========================================================================
130.\"
131.IX Title "BIO_f_md 3"
aac4ff6f 132.TH BIO_f_md 3 "2008-09-06" "0.9.8h" "OpenSSL"
984263bc 133.SH "NAME"
74dab6c2 134BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx \- message digest BIO filter
984263bc 135.SH "SYNOPSIS"
8b0cefbb 136.IX Header "SYNOPSIS"
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137.Vb 2
138\& #include <openssl/bio.h>
139\& #include <openssl/evp.h>
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140.Ve
141.PP
142.Vb 4
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143\& BIO_METHOD * BIO_f_md(void);
144\& int BIO_set_md(BIO *b,EVP_MD *md);
145\& int BIO_get_md(BIO *b,EVP_MD **mdp);
146\& int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp);
147.Ve
148.SH "DESCRIPTION"
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149.IX Header "DESCRIPTION"
150\&\fIBIO_f_md()\fR returns the message digest \s-1BIO\s0 method. This is a filter
151\&\s-1BIO\s0 that digests any data passed through it, it is a \s-1BIO\s0 wrapper
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152for the digest routines \fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR
153and \fIEVP_DigestFinal()\fR.
154.PP
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155Any data written or read through a digest \s-1BIO\s0 using \fIBIO_read()\fR and
156\&\fIBIO_write()\fR is digested.
984263bc 157.PP
8b0cefbb 158\&\fIBIO_gets()\fR, if its \fBsize\fR parameter is large enough finishes the
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159digest calculation and returns the digest value. \fIBIO_puts()\fR is
160not supported.
161.PP
8b0cefbb 162\&\fIBIO_reset()\fR reinitialises a digest \s-1BIO\s0.
984263bc 163.PP
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164\&\fIBIO_set_md()\fR sets the message digest of \s-1BIO\s0 \fBb\fR to \fBmd\fR: this
165must be called to initialize a digest \s-1BIO\s0 before any data is
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166passed through it. It is a \fIBIO_ctrl()\fR macro.
167.PP
8b0cefbb 168\&\fIBIO_get_md()\fR places the a pointer to the digest BIOs digest method
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169in \fBmdp\fR, it is a \fIBIO_ctrl()\fR macro.
170.PP
8b0cefbb 171\&\fIBIO_get_md_ctx()\fR returns the digest BIOs context into \fBmdcp\fR.
984263bc 172.SH "NOTES"
8b0cefbb 173.IX Header "NOTES"
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174The context returned by \fIBIO_get_md_ctx()\fR can be used in calls
175to \fIEVP_DigestFinal()\fR and also the signature routines \fIEVP_SignFinal()\fR
176and \fIEVP_VerifyFinal()\fR.
177.PP
178The context returned by \fIBIO_get_md_ctx()\fR is an internal context
179structure. Changes made to this context will affect the digest
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180\&\s-1BIO\s0 itself and the context pointer will become invalid when the digest
181\&\s-1BIO\s0 is freed.
984263bc 182.PP
8b0cefbb 183After the digest has been retrieved from a digest \s-1BIO\s0 it must be
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184reinitialized by calling \fIBIO_reset()\fR, or \fIBIO_set_md()\fR before any more
185data is passed through it.
186.PP
187If an application needs to call \fIBIO_gets()\fR or \fIBIO_puts()\fR through
188a chain containing digest BIOs then this can be done by prepending
8b0cefbb 189a buffering \s-1BIO\s0.
984263bc 190.SH "RETURN VALUES"
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191.IX Header "RETURN VALUES"
192\&\fIBIO_f_md()\fR returns the digest \s-1BIO\s0 method.
984263bc 193.PP
8b0cefbb 194\&\fIBIO_set_md()\fR, \fIBIO_get_md()\fR and \fIBIO_md_ctx()\fR return 1 for success and
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1950 for failure.
196.SH "EXAMPLES"
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197.IX Header "EXAMPLES"
198The following example creates a \s-1BIO\s0 chain containing an \s-1SHA1\s0 and \s-1MD5\s0
199digest \s-1BIO\s0 and passes the string \*(L"Hello World\*(R" through it. Error
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200checking has been omitted for clarity.
201.PP
aac4ff6f 202.Vb 14
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203\& BIO *bio, *mdtmp;
204\& char message[] = "Hello World";
205\& bio = BIO_new(BIO_s_null());
206\& mdtmp = BIO_new(BIO_f_md());
207\& BIO_set_md(mdtmp, EVP_sha1());
208\& /* For BIO_push() we want to append the sink BIO and keep a note of
209\& * the start of the chain.
210\& */
211\& bio = BIO_push(mdtmp, bio);
212\& mdtmp = BIO_new(BIO_f_md());
213\& BIO_set_md(mdtmp, EVP_md5());
214\& bio = BIO_push(mdtmp, bio);
215\& /* Note: mdtmp can now be discarded */
216\& BIO_write(bio, message, strlen(message));
217.Ve
8b0cefbb 218.PP
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219The next example digests data by reading through a chain instead:
220.PP
aac4ff6f 221.Vb 14
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222\& BIO *bio, *mdtmp;
223\& char buf[1024];
224\& int rdlen;
225\& bio = BIO_new_file(file, "rb");
226\& mdtmp = BIO_new(BIO_f_md());
227\& BIO_set_md(mdtmp, EVP_sha1());
228\& bio = BIO_push(mdtmp, bio);
229\& mdtmp = BIO_new(BIO_f_md());
230\& BIO_set_md(mdtmp, EVP_md5());
231\& bio = BIO_push(mdtmp, bio);
232\& do {
233\& rdlen = BIO_read(bio, buf, sizeof(buf));
234\& /* Might want to do something with the data here */
235\& } while(rdlen > 0);
236.Ve
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237.PP
238This next example retrieves the message digests from a \s-1BIO\s0 chain and
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239outputs them. This could be used with the examples above.
240.PP
aac4ff6f 241.Vb 16
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242\& BIO *mdtmp;
243\& unsigned char mdbuf[EVP_MAX_MD_SIZE];
244\& int mdlen;
245\& int i;
246\& mdtmp = bio; /* Assume bio has previously been set up */
247\& do {
248\& EVP_MD *md;
249\& mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
250\& if(!mdtmp) break;
251\& BIO_get_md(mdtmp, &md);
252\& printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));
253\& mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
254\& for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);
255\& printf("\en");
256\& mdtmp = BIO_next(mdtmp);
257\& } while(mdtmp);
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258.Ve
259.PP
260.Vb 1
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261\& BIO_free_all(bio);
262.Ve
263.SH "BUGS"
8b0cefbb 264.IX Header "BUGS"
984263bc 265The lack of support for \fIBIO_puts()\fR and the non standard behaviour of
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266\&\fIBIO_gets()\fR could be regarded as anomalous. It could be argued that \fIBIO_gets()\fR
267and \fIBIO_puts()\fR should be passed to the next \s-1BIO\s0 in the chain and digest
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268the data passed through and that digests should be retrieved using a
269separate \fIBIO_ctrl()\fR call.
270.SH "SEE ALSO"
271.IX Header "SEE ALSO"
8b0cefbb 272\&\s-1TBA\s0