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| 124 | .\" ======================================================================== |
| 125 | .\" |
| 126 | .IX Title "BIO_f_md 3" |
| 127 | .TH BIO_f_md 3 "2012-01-04" "1.0.0f" "OpenSSL" |
| 128 | .\" For nroff, turn off justification. Always turn off hyphenation; it makes |
| 129 | .\" way too many mistakes in technical documents. |
| 130 | .if n .ad l |
| 131 | .nh |
| 132 | .SH "NAME" |
| 133 | BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx \- message digest BIO filter |
| 134 | .SH "SYNOPSIS" |
| 135 | .IX Header "SYNOPSIS" |
| 136 | .Vb 2 |
| 137 | \& #include <openssl/bio.h> |
| 138 | \& #include <openssl/evp.h> |
| 139 | \& |
| 140 | \& BIO_METHOD * BIO_f_md(void); |
| 141 | \& int BIO_set_md(BIO *b,EVP_MD *md); |
| 142 | \& int BIO_get_md(BIO *b,EVP_MD **mdp); |
| 143 | \& int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp); |
| 144 | .Ve |
| 145 | .SH "DESCRIPTION" |
| 146 | .IX Header "DESCRIPTION" |
| 147 | \&\fIBIO_f_md()\fR returns the message digest \s-1BIO\s0 method. This is a filter |
| 148 | \&\s-1BIO\s0 that digests any data passed through it, it is a \s-1BIO\s0 wrapper |
| 149 | for the digest routines \fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR |
| 150 | and \fIEVP_DigestFinal()\fR. |
| 151 | .PP |
| 152 | Any data written or read through a digest \s-1BIO\s0 using \fIBIO_read()\fR and |
| 153 | \&\fIBIO_write()\fR is digested. |
| 154 | .PP |
| 155 | \&\fIBIO_gets()\fR, if its \fBsize\fR parameter is large enough finishes the |
| 156 | digest calculation and returns the digest value. \fIBIO_puts()\fR is |
| 157 | not supported. |
| 158 | .PP |
| 159 | \&\fIBIO_reset()\fR reinitialises a digest \s-1BIO\s0. |
| 160 | .PP |
| 161 | \&\fIBIO_set_md()\fR sets the message digest of \s-1BIO\s0 \fBb\fR to \fBmd\fR: this |
| 162 | must be called to initialize a digest \s-1BIO\s0 before any data is |
| 163 | passed through it. It is a \fIBIO_ctrl()\fR macro. |
| 164 | .PP |
| 165 | \&\fIBIO_get_md()\fR places the a pointer to the digest BIOs digest method |
| 166 | in \fBmdp\fR, it is a \fIBIO_ctrl()\fR macro. |
| 167 | .PP |
| 168 | \&\fIBIO_get_md_ctx()\fR returns the digest BIOs context into \fBmdcp\fR. |
| 169 | .SH "NOTES" |
| 170 | .IX Header "NOTES" |
| 171 | The context returned by \fIBIO_get_md_ctx()\fR can be used in calls |
| 172 | to \fIEVP_DigestFinal()\fR and also the signature routines \fIEVP_SignFinal()\fR |
| 173 | and \fIEVP_VerifyFinal()\fR. |
| 174 | .PP |
| 175 | The context returned by \fIBIO_get_md_ctx()\fR is an internal context |
| 176 | structure. Changes made to this context will affect the digest |
| 177 | \&\s-1BIO\s0 itself and the context pointer will become invalid when the digest |
| 178 | \&\s-1BIO\s0 is freed. |
| 179 | .PP |
| 180 | After the digest has been retrieved from a digest \s-1BIO\s0 it must be |
| 181 | reinitialized by calling \fIBIO_reset()\fR, or \fIBIO_set_md()\fR before any more |
| 182 | data is passed through it. |
| 183 | .PP |
| 184 | If an application needs to call \fIBIO_gets()\fR or \fIBIO_puts()\fR through |
| 185 | a chain containing digest BIOs then this can be done by prepending |
| 186 | a buffering \s-1BIO\s0. |
| 187 | .PP |
| 188 | Before OpenSSL 1.0.0 the call to \fIBIO_get_md_ctx()\fR would only work if the \s-1BIO\s0 |
| 189 | had been initialized for example by calling \fIBIO_set_md()\fR ). In OpenSSL |
| 190 | 1.0.0 and later the context is always returned and the \s-1BIO\s0 is state is set |
| 191 | to initialized. This allows applications to initialize the context externally |
| 192 | if the standard calls such as \fIBIO_set_md()\fR are not sufficiently flexible. |
| 193 | .SH "RETURN VALUES" |
| 194 | .IX Header "RETURN VALUES" |
| 195 | \&\fIBIO_f_md()\fR returns the digest \s-1BIO\s0 method. |
| 196 | .PP |
| 197 | \&\fIBIO_set_md()\fR, \fIBIO_get_md()\fR and \fIBIO_md_ctx()\fR return 1 for success and |
| 198 | 0 for failure. |
| 199 | .SH "EXAMPLES" |
| 200 | .IX Header "EXAMPLES" |
| 201 | The following example creates a \s-1BIO\s0 chain containing an \s-1SHA1\s0 and \s-1MD5\s0 |
| 202 | digest \s-1BIO\s0 and passes the string \*(L"Hello World\*(R" through it. Error |
| 203 | checking has been omitted for clarity. |
| 204 | .PP |
| 205 | .Vb 10 |
| 206 | \& BIO *bio, *mdtmp; |
| 207 | \& char message[] = "Hello World"; |
| 208 | \& bio = BIO_new(BIO_s_null()); |
| 209 | \& mdtmp = BIO_new(BIO_f_md()); |
| 210 | \& BIO_set_md(mdtmp, EVP_sha1()); |
| 211 | \& /* For BIO_push() we want to append the sink BIO and keep a note of |
| 212 | \& * the start of the chain. |
| 213 | \& */ |
| 214 | \& bio = BIO_push(mdtmp, bio); |
| 215 | \& mdtmp = BIO_new(BIO_f_md()); |
| 216 | \& BIO_set_md(mdtmp, EVP_md5()); |
| 217 | \& bio = BIO_push(mdtmp, bio); |
| 218 | \& /* Note: mdtmp can now be discarded */ |
| 219 | \& BIO_write(bio, message, strlen(message)); |
| 220 | .Ve |
| 221 | .PP |
| 222 | The next example digests data by reading through a chain instead: |
| 223 | .PP |
| 224 | .Vb 10 |
| 225 | \& BIO *bio, *mdtmp; |
| 226 | \& char buf[1024]; |
| 227 | \& int rdlen; |
| 228 | \& bio = BIO_new_file(file, "rb"); |
| 229 | \& mdtmp = BIO_new(BIO_f_md()); |
| 230 | \& BIO_set_md(mdtmp, EVP_sha1()); |
| 231 | \& bio = BIO_push(mdtmp, bio); |
| 232 | \& mdtmp = BIO_new(BIO_f_md()); |
| 233 | \& BIO_set_md(mdtmp, EVP_md5()); |
| 234 | \& bio = BIO_push(mdtmp, bio); |
| 235 | \& do { |
| 236 | \& rdlen = BIO_read(bio, buf, sizeof(buf)); |
| 237 | \& /* Might want to do something with the data here */ |
| 238 | \& } while(rdlen > 0); |
| 239 | .Ve |
| 240 | .PP |
| 241 | This next example retrieves the message digests from a \s-1BIO\s0 chain and |
| 242 | outputs them. This could be used with the examples above. |
| 243 | .PP |
| 244 | .Vb 10 |
| 245 | \& BIO *mdtmp; |
| 246 | \& unsigned char mdbuf[EVP_MAX_MD_SIZE]; |
| 247 | \& int mdlen; |
| 248 | \& int i; |
| 249 | \& mdtmp = bio; /* Assume bio has previously been set up */ |
| 250 | \& do { |
| 251 | \& EVP_MD *md; |
| 252 | \& mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD); |
| 253 | \& if(!mdtmp) break; |
| 254 | \& BIO_get_md(mdtmp, &md); |
| 255 | \& printf("%s digest", OBJ_nid2sn(EVP_MD_type(md))); |
| 256 | \& mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE); |
| 257 | \& for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]); |
| 258 | \& printf("\en"); |
| 259 | \& mdtmp = BIO_next(mdtmp); |
| 260 | \& } while(mdtmp); |
| 261 | \& |
| 262 | \& BIO_free_all(bio); |
| 263 | .Ve |
| 264 | .SH "BUGS" |
| 265 | .IX Header "BUGS" |
| 266 | The lack of support for \fIBIO_puts()\fR and the non standard behaviour of |
| 267 | \&\fIBIO_gets()\fR could be regarded as anomalous. It could be argued that \fIBIO_gets()\fR |
| 268 | and \fIBIO_puts()\fR should be passed to the next \s-1BIO\s0 in the chain and digest |
| 269 | the data passed through and that digests should be retrieved using a |
| 270 | separate \fIBIO_ctrl()\fR call. |
| 271 | .SH "SEE ALSO" |
| 272 | .IX Header "SEE ALSO" |
| 273 | \&\s-1TBA\s0 |