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| 124 | .\" ======================================================================== |
| 125 | .\" |
| 126 | .IX Title "DH_set_method 3" |
| 127 | .TH DH_set_method 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 | DH_set_default_method, DH_get_default_method, |
| 134 | DH_set_method, DH_new_method, DH_OpenSSL \- select DH method |
| 135 | .SH "SYNOPSIS" |
| 136 | .IX Header "SYNOPSIS" |
| 137 | .Vb 2 |
| 138 | \& #include <openssl/dh.h> |
| 139 | \& #include <openssl/engine.h> |
| 140 | \& |
| 141 | \& void DH_set_default_method(const DH_METHOD *meth); |
| 142 | \& |
| 143 | \& const DH_METHOD *DH_get_default_method(void); |
| 144 | \& |
| 145 | \& int DH_set_method(DH *dh, const DH_METHOD *meth); |
| 146 | \& |
| 147 | \& DH *DH_new_method(ENGINE *engine); |
| 148 | \& |
| 149 | \& const DH_METHOD *DH_OpenSSL(void); |
| 150 | .Ve |
| 151 | .SH "DESCRIPTION" |
| 152 | .IX Header "DESCRIPTION" |
| 153 | A \fB\s-1DH_METHOD\s0\fR specifies the functions that OpenSSL uses for Diffie-Hellman |
| 154 | operations. By modifying the method, alternative implementations |
| 155 | such as hardware accelerators may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for |
| 156 | important information about how these \s-1DH\s0 \s-1API\s0 functions are affected by the use |
| 157 | of \fB\s-1ENGINE\s0\fR \s-1API\s0 calls. |
| 158 | .PP |
| 159 | Initially, the default \s-1DH_METHOD\s0 is the OpenSSL internal implementation, as |
| 160 | returned by \fIDH_OpenSSL()\fR. |
| 161 | .PP |
| 162 | \&\fIDH_set_default_method()\fR makes \fBmeth\fR the default method for all \s-1DH\s0 |
| 163 | structures created later. \fB\s-1NB\s0\fR: This is true only whilst no \s-1ENGINE\s0 has been set |
| 164 | as a default for \s-1DH\s0, so this function is no longer recommended. |
| 165 | .PP |
| 166 | \&\fIDH_get_default_method()\fR returns a pointer to the current default \s-1DH_METHOD\s0. |
| 167 | However, the meaningfulness of this result is dependent on whether the \s-1ENGINE\s0 |
| 168 | \&\s-1API\s0 is being used, so this function is no longer recommended. |
| 169 | .PP |
| 170 | \&\fIDH_set_method()\fR selects \fBmeth\fR to perform all operations using the key \fBdh\fR. |
| 171 | This will replace the \s-1DH_METHOD\s0 used by the \s-1DH\s0 key and if the previous method |
| 172 | was supplied by an \s-1ENGINE\s0, the handle to that \s-1ENGINE\s0 will be released during the |
| 173 | change. It is possible to have \s-1DH\s0 keys that only work with certain \s-1DH_METHOD\s0 |
| 174 | implementations (eg. from an \s-1ENGINE\s0 module that supports embedded |
| 175 | hardware-protected keys), and in such cases attempting to change the \s-1DH_METHOD\s0 |
| 176 | for the key can have unexpected results. |
| 177 | .PP |
| 178 | \&\fIDH_new_method()\fR allocates and initializes a \s-1DH\s0 structure so that \fBengine\fR will |
| 179 | be used for the \s-1DH\s0 operations. If \fBengine\fR is \s-1NULL\s0, the default \s-1ENGINE\s0 for \s-1DH\s0 |
| 180 | operations is used, and if no default \s-1ENGINE\s0 is set, the \s-1DH_METHOD\s0 controlled by |
| 181 | \&\fIDH_set_default_method()\fR is used. |
| 182 | .SH "THE DH_METHOD STRUCTURE" |
| 183 | .IX Header "THE DH_METHOD STRUCTURE" |
| 184 | .Vb 4 |
| 185 | \& typedef struct dh_meth_st |
| 186 | \& { |
| 187 | \& /* name of the implementation */ |
| 188 | \& const char *name; |
| 189 | \& |
| 190 | \& /* generate private and public DH values for key agreement */ |
| 191 | \& int (*generate_key)(DH *dh); |
| 192 | \& |
| 193 | \& /* compute shared secret */ |
| 194 | \& int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh); |
| 195 | \& |
| 196 | \& /* compute r = a ^ p mod m (May be NULL for some implementations) */ |
| 197 | \& int (*bn_mod_exp)(DH *dh, BIGNUM *r, BIGNUM *a, const BIGNUM *p, |
| 198 | \& const BIGNUM *m, BN_CTX *ctx, |
| 199 | \& BN_MONT_CTX *m_ctx); |
| 200 | \& |
| 201 | \& /* called at DH_new */ |
| 202 | \& int (*init)(DH *dh); |
| 203 | \& |
| 204 | \& /* called at DH_free */ |
| 205 | \& int (*finish)(DH *dh); |
| 206 | \& |
| 207 | \& int flags; |
| 208 | \& |
| 209 | \& char *app_data; /* ?? */ |
| 210 | \& |
| 211 | \& } DH_METHOD; |
| 212 | .Ve |
| 213 | .SH "RETURN VALUES" |
| 214 | .IX Header "RETURN VALUES" |
| 215 | \&\fIDH_OpenSSL()\fR and \fIDH_get_default_method()\fR return pointers to the respective |
| 216 | \&\fB\s-1DH_METHOD\s0\fRs. |
| 217 | .PP |
| 218 | \&\fIDH_set_default_method()\fR returns no value. |
| 219 | .PP |
| 220 | \&\fIDH_set_method()\fR returns non-zero if the provided \fBmeth\fR was successfully set as |
| 221 | the method for \fBdh\fR (including unloading the \s-1ENGINE\s0 handle if the previous |
| 222 | method was supplied by an \s-1ENGINE\s0). |
| 223 | .PP |
| 224 | \&\fIDH_new_method()\fR returns \s-1NULL\s0 and sets an error code that can be obtained by |
| 225 | \&\fIERR_get_error\fR\|(3) if the allocation fails. Otherwise it |
| 226 | returns a pointer to the newly allocated structure. |
| 227 | .SH "NOTES" |
| 228 | .IX Header "NOTES" |
| 229 | As of version 0.9.7, \s-1DH_METHOD\s0 implementations are grouped together with other |
| 230 | algorithmic APIs (eg. \s-1RSA_METHOD\s0, \s-1EVP_CIPHER\s0, etc) in \fB\s-1ENGINE\s0\fR modules. If a |
| 231 | default \s-1ENGINE\s0 is specified for \s-1DH\s0 functionality using an \s-1ENGINE\s0 \s-1API\s0 function, |
| 232 | that will override any \s-1DH\s0 defaults set using the \s-1DH\s0 \s-1API\s0 (ie. |
| 233 | \&\fIDH_set_default_method()\fR). For this reason, the \s-1ENGINE\s0 \s-1API\s0 is the recommended way |
| 234 | to control default implementations for use in \s-1DH\s0 and other cryptographic |
| 235 | algorithms. |
| 236 | .SH "SEE ALSO" |
| 237 | .IX Header "SEE ALSO" |
| 238 | \&\fIdh\fR\|(3), \fIDH_new\fR\|(3) |
| 239 | .SH "HISTORY" |
| 240 | .IX Header "HISTORY" |
| 241 | \&\fIDH_set_default_method()\fR, \fIDH_get_default_method()\fR, \fIDH_set_method()\fR, |
| 242 | \&\fIDH_new_method()\fR and \fIDH_OpenSSL()\fR were added in OpenSSL 0.9.4. |
| 243 | .PP |
| 244 | \&\fIDH_set_default_openssl_method()\fR and \fIDH_get_default_openssl_method()\fR replaced |
| 245 | \&\fIDH_set_default_method()\fR and \fIDH_get_default_method()\fR respectively, and |
| 246 | \&\fIDH_set_method()\fR and \fIDH_new_method()\fR were altered to use \fB\s-1ENGINE\s0\fRs rather than |
| 247 | \&\fB\s-1DH_METHOD\s0\fRs during development of the engine version of OpenSSL 0.9.6. For |
| 248 | 0.9.7, the handling of defaults in the \s-1ENGINE\s0 \s-1API\s0 was restructured so that this |
| 249 | change was reversed, and behaviour of the other functions resembled more closely |
| 250 | the previous behaviour. The behaviour of defaults in the \s-1ENGINE\s0 \s-1API\s0 now |
| 251 | transparently overrides the behaviour of defaults in the \s-1DH\s0 \s-1API\s0 without |
| 252 | requiring changing these function prototypes. |