Update files for OpenSSL-1.0.0f import.
[dragonfly.git] / secure / lib / libcrypto / man / DH_set_method.3
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124.\" ========================================================================
125.\"
126.IX Title "DH_set_method 3"
e3261593 127.TH DH_set_method 3 "2012-01-04" "1.0.0f" "OpenSSL"
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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
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132.SH "NAME"
133DH_set_default_method, DH_get_default_method,
74dab6c2 134DH_set_method, DH_new_method, DH_OpenSSL \- select DH method
984263bc 135.SH "SYNOPSIS"
8b0cefbb 136.IX Header "SYNOPSIS"
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137.Vb 2
138\& #include <openssl/dh.h>
139\& #include <openssl/engine.h>
e257b235 140\&
984263bc 141\& void DH_set_default_method(const DH_METHOD *meth);
e257b235 142\&
984263bc 143\& const DH_METHOD *DH_get_default_method(void);
e257b235 144\&
984263bc 145\& int DH_set_method(DH *dh, const DH_METHOD *meth);
e257b235 146\&
984263bc 147\& DH *DH_new_method(ENGINE *engine);
e257b235 148\&
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149\& const DH_METHOD *DH_OpenSSL(void);
150.Ve
151.SH "DESCRIPTION"
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152.IX Header "DESCRIPTION"
153A \fB\s-1DH_METHOD\s0\fR specifies the functions that OpenSSL uses for Diffie-Hellman
984263bc 154operations. By modifying the method, alternative implementations
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155such as hardware accelerators may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for
156important information about how these \s-1DH\s0 \s-1API\s0 functions are affected by the use
157of \fB\s-1ENGINE\s0\fR \s-1API\s0 calls.
984263bc 158.PP
8b0cefbb 159Initially, the default \s-1DH_METHOD\s0 is the OpenSSL internal implementation, as
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160returned by \fIDH_OpenSSL()\fR.
161.PP
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162\&\fIDH_set_default_method()\fR makes \fBmeth\fR the default method for all \s-1DH\s0
163structures created later. \fB\s-1NB\s0\fR: This is true only whilst no \s-1ENGINE\s0 has been set
164as a default for \s-1DH\s0, so this function is no longer recommended.
984263bc 165.PP
8b0cefbb 166\&\fIDH_get_default_method()\fR returns a pointer to the current default \s-1DH_METHOD\s0.
aac4ff6f 167However, the meaningfulness of this result is dependent on whether the \s-1ENGINE\s0
8b0cefbb 168\&\s-1API\s0 is being used, so this function is no longer recommended.
984263bc 169.PP
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170\&\fIDH_set_method()\fR selects \fBmeth\fR to perform all operations using the key \fBdh\fR.
171This will replace the \s-1DH_METHOD\s0 used by the \s-1DH\s0 key and if the previous method
172was supplied by an \s-1ENGINE\s0, the handle to that \s-1ENGINE\s0 will be released during the
173change. It is possible to have \s-1DH\s0 keys that only work with certain \s-1DH_METHOD\s0
174implementations (eg. from an \s-1ENGINE\s0 module that supports embedded
175hardware-protected keys), and in such cases attempting to change the \s-1DH_METHOD\s0
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176for the key can have unexpected results.
177.PP
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178\&\fIDH_new_method()\fR allocates and initializes a \s-1DH\s0 structure so that \fBengine\fR will
179be used for the \s-1DH\s0 operations. If \fBengine\fR is \s-1NULL\s0, the default \s-1ENGINE\s0 for \s-1DH\s0
180operations 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.
984263bc 182.SH "THE DH_METHOD STRUCTURE"
8b0cefbb 183.IX Header "THE DH_METHOD STRUCTURE"
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184.Vb 4
185\& typedef struct dh_meth_st
186\& {
187\& /* name of the implementation */
188\& const char *name;
e257b235 189\&
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190\& /* generate private and public DH values for key agreement */
191\& int (*generate_key)(DH *dh);
e257b235 192\&
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193\& /* compute shared secret */
194\& int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh);
e257b235 195\&
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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);
e257b235 200\&
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201\& /* called at DH_new */
202\& int (*init)(DH *dh);
e257b235 203\&
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204\& /* called at DH_free */
205\& int (*finish)(DH *dh);
e257b235 206\&
984263bc 207\& int flags;
e257b235 208\&
984263bc 209\& char *app_data; /* ?? */
e257b235 210\&
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211\& } DH_METHOD;
212.Ve
213.SH "RETURN VALUES"
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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.
984263bc 217.PP
8b0cefbb 218\&\fIDH_set_default_method()\fR returns no value.
984263bc 219.PP
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220\&\fIDH_set_method()\fR returns non-zero if the provided \fBmeth\fR was successfully set as
221the method for \fBdh\fR (including unloading the \s-1ENGINE\s0 handle if the previous
222method was supplied by an \s-1ENGINE\s0).
984263bc 223.PP
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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
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226returns a pointer to the newly allocated structure.
227.SH "NOTES"
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228.IX Header "NOTES"
229As of version 0.9.7, \s-1DH_METHOD\s0 implementations are grouped together with other
230algorithmic APIs (eg. \s-1RSA_METHOD\s0, \s-1EVP_CIPHER\s0, etc) in \fB\s-1ENGINE\s0\fR modules. If a
231default \s-1ENGINE\s0 is specified for \s-1DH\s0 functionality using an \s-1ENGINE\s0 \s-1API\s0 function,
232that 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
234to control default implementations for use in \s-1DH\s0 and other cryptographic
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235algorithms.
236.SH "SEE ALSO"
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237.IX Header "SEE ALSO"
238\&\fIdh\fR\|(3), \fIDH_new\fR\|(3)
984263bc 239.SH "HISTORY"
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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.
984263bc 243.PP
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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
2480.9.7, the handling of defaults in the \s-1ENGINE\s0 \s-1API\s0 was restructured so that this
984263bc 249change was reversed, and behaviour of the other functions resembled more closely
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250the previous behaviour. The behaviour of defaults in the \s-1ENGINE\s0 \s-1API\s0 now
251transparently overrides the behaviour of defaults in the \s-1DH\s0 \s-1API\s0 without
984263bc 252requiring changing these function prototypes.