Update build for OpenSSL-0.9.8j upgrade.
[dragonfly.git] / secure / lib / libcrypto / man / DH_set_method.3
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132.\" ========================================================================
133.\"
134.IX Title "DH_set_method 3"
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135.TH DH_set_method 3 "2009-01-11" "0.9.8j" "OpenSSL"
136.\" For nroff, turn off justification. Always turn off hyphenation; it makes
137.\" way too many mistakes in technical documents.
138.if n .ad l
139.nh
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140.SH "NAME"
141DH_set_default_method, DH_get_default_method,
74dab6c2 142DH_set_method, DH_new_method, DH_OpenSSL \- select DH method
984263bc 143.SH "SYNOPSIS"
8b0cefbb 144.IX Header "SYNOPSIS"
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145.Vb 2
146\& #include <openssl/dh.h>
147\& #include <openssl/engine.h>
e257b235 148\&
984263bc 149\& void DH_set_default_method(const DH_METHOD *meth);
e257b235 150\&
984263bc 151\& const DH_METHOD *DH_get_default_method(void);
e257b235 152\&
984263bc 153\& int DH_set_method(DH *dh, const DH_METHOD *meth);
e257b235 154\&
984263bc 155\& DH *DH_new_method(ENGINE *engine);
e257b235 156\&
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157\& const DH_METHOD *DH_OpenSSL(void);
158.Ve
159.SH "DESCRIPTION"
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160.IX Header "DESCRIPTION"
161A \fB\s-1DH_METHOD\s0\fR specifies the functions that OpenSSL uses for Diffie-Hellman
984263bc 162operations. By modifying the method, alternative implementations
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163such as hardware accelerators may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for
164important information about how these \s-1DH\s0 \s-1API\s0 functions are affected by the use
165of \fB\s-1ENGINE\s0\fR \s-1API\s0 calls.
984263bc 166.PP
8b0cefbb 167Initially, the default \s-1DH_METHOD\s0 is the OpenSSL internal implementation, as
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168returned by \fIDH_OpenSSL()\fR.
169.PP
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170\&\fIDH_set_default_method()\fR makes \fBmeth\fR the default method for all \s-1DH\s0
171structures created later. \fB\s-1NB\s0\fR: This is true only whilst no \s-1ENGINE\s0 has been set
172as a default for \s-1DH\s0, so this function is no longer recommended.
984263bc 173.PP
8b0cefbb 174\&\fIDH_get_default_method()\fR returns a pointer to the current default \s-1DH_METHOD\s0.
aac4ff6f 175However, the meaningfulness of this result is dependent on whether the \s-1ENGINE\s0
8b0cefbb 176\&\s-1API\s0 is being used, so this function is no longer recommended.
984263bc 177.PP
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178\&\fIDH_set_method()\fR selects \fBmeth\fR to perform all operations using the key \fBdh\fR.
179This will replace the \s-1DH_METHOD\s0 used by the \s-1DH\s0 key and if the previous method
180was supplied by an \s-1ENGINE\s0, the handle to that \s-1ENGINE\s0 will be released during the
181change. It is possible to have \s-1DH\s0 keys that only work with certain \s-1DH_METHOD\s0
182implementations (eg. from an \s-1ENGINE\s0 module that supports embedded
183hardware-protected keys), and in such cases attempting to change the \s-1DH_METHOD\s0
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184for the key can have unexpected results.
185.PP
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186\&\fIDH_new_method()\fR allocates and initializes a \s-1DH\s0 structure so that \fBengine\fR will
187be used for the \s-1DH\s0 operations. If \fBengine\fR is \s-1NULL\s0, the default \s-1ENGINE\s0 for \s-1DH\s0
188operations is used, and if no default \s-1ENGINE\s0 is set, the \s-1DH_METHOD\s0 controlled by
189\&\fIDH_set_default_method()\fR is used.
984263bc 190.SH "THE DH_METHOD STRUCTURE"
8b0cefbb 191.IX Header "THE DH_METHOD STRUCTURE"
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192.Vb 4
193\& typedef struct dh_meth_st
194\& {
195\& /* name of the implementation */
196\& const char *name;
e257b235 197\&
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198\& /* generate private and public DH values for key agreement */
199\& int (*generate_key)(DH *dh);
e257b235 200\&
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201\& /* compute shared secret */
202\& int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh);
e257b235 203\&
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204\& /* compute r = a ^ p mod m (May be NULL for some implementations) */
205\& int (*bn_mod_exp)(DH *dh, BIGNUM *r, BIGNUM *a, const BIGNUM *p,
206\& const BIGNUM *m, BN_CTX *ctx,
207\& BN_MONT_CTX *m_ctx);
e257b235 208\&
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209\& /* called at DH_new */
210\& int (*init)(DH *dh);
e257b235 211\&
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212\& /* called at DH_free */
213\& int (*finish)(DH *dh);
e257b235 214\&
984263bc 215\& int flags;
e257b235 216\&
984263bc 217\& char *app_data; /* ?? */
e257b235 218\&
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219\& } DH_METHOD;
220.Ve
221.SH "RETURN VALUES"
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222.IX Header "RETURN VALUES"
223\&\fIDH_OpenSSL()\fR and \fIDH_get_default_method()\fR return pointers to the respective
224\&\fB\s-1DH_METHOD\s0\fRs.
984263bc 225.PP
8b0cefbb 226\&\fIDH_set_default_method()\fR returns no value.
984263bc 227.PP
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228\&\fIDH_set_method()\fR returns non-zero if the provided \fBmeth\fR was successfully set as
229the method for \fBdh\fR (including unloading the \s-1ENGINE\s0 handle if the previous
230method was supplied by an \s-1ENGINE\s0).
984263bc 231.PP
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232\&\fIDH_new_method()\fR returns \s-1NULL\s0 and sets an error code that can be obtained by
233\&\fIERR_get_error\fR\|(3) if the allocation fails. Otherwise it
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234returns a pointer to the newly allocated structure.
235.SH "NOTES"
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236.IX Header "NOTES"
237As of version 0.9.7, \s-1DH_METHOD\s0 implementations are grouped together with other
238algorithmic APIs (eg. \s-1RSA_METHOD\s0, \s-1EVP_CIPHER\s0, etc) in \fB\s-1ENGINE\s0\fR modules. If a
239default \s-1ENGINE\s0 is specified for \s-1DH\s0 functionality using an \s-1ENGINE\s0 \s-1API\s0 function,
240that will override any \s-1DH\s0 defaults set using the \s-1DH\s0 \s-1API\s0 (ie.
241\&\fIDH_set_default_method()\fR). For this reason, the \s-1ENGINE\s0 \s-1API\s0 is the recommended way
242to control default implementations for use in \s-1DH\s0 and other cryptographic
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243algorithms.
244.SH "SEE ALSO"
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245.IX Header "SEE ALSO"
246\&\fIdh\fR\|(3), \fIDH_new\fR\|(3)
984263bc 247.SH "HISTORY"
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248.IX Header "HISTORY"
249\&\fIDH_set_default_method()\fR, \fIDH_get_default_method()\fR, \fIDH_set_method()\fR,
250\&\fIDH_new_method()\fR and \fIDH_OpenSSL()\fR were added in OpenSSL 0.9.4.
984263bc 251.PP
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252\&\fIDH_set_default_openssl_method()\fR and \fIDH_get_default_openssl_method()\fR replaced
253\&\fIDH_set_default_method()\fR and \fIDH_get_default_method()\fR respectively, and
254\&\fIDH_set_method()\fR and \fIDH_new_method()\fR were altered to use \fB\s-1ENGINE\s0\fRs rather than
255\&\fB\s-1DH_METHOD\s0\fRs during development of the engine version of OpenSSL 0.9.6. For
2560.9.7, the handling of defaults in the \s-1ENGINE\s0 \s-1API\s0 was restructured so that this
984263bc 257change was reversed, and behaviour of the other functions resembled more closely
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258the previous behaviour. The behaviour of defaults in the \s-1ENGINE\s0 \s-1API\s0 now
259transparently overrides the behaviour of defaults in the \s-1DH\s0 \s-1API\s0 without
984263bc 260requiring changing these function prototypes.