281 lines
9.4 KiB
Groff
281 lines
9.4 KiB
Groff
.\" $NetBSD: DH_set_method.3,v 1.12 2003/07/24 14:16:38 itojun Exp $
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.\" ======================================================================
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.\"
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.IX Title "DH_set_method 3"
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.TH DH_set_method 3 "0.9.7b" "2002-10-29" "OpenSSL"
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.UC
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.SH "NAME"
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DH_set_default_method, DH_get_default_method,
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DH_set_method, DH_new_method, DH_OpenSSL \- select \s-1DH\s0 method
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.SH "LIBRARY"
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libcrypto, -lcrypto
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 2
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\& #include <openssl/dh.h>
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\& #include <openssl/engine.h>
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.Ve
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.Vb 1
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\& void DH_set_default_method(const DH_METHOD *meth);
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.Ve
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.Vb 1
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\& const DH_METHOD *DH_get_default_method(void);
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.Ve
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.Vb 1
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\& int DH_set_method(DH *dh, const DH_METHOD *meth);
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.Ve
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.Vb 1
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\& DH *DH_new_method(ENGINE *engine);
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.Ve
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.Vb 1
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\& const DH_METHOD *DH_OpenSSL(void);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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A \fB\s-1DH_METHOD\s0\fR specifies the functions that OpenSSL uses for Diffie-Hellman
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operations. By modifying the method, alternative implementations
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such as hardware accelerators may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for
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important information about how these \s-1DH\s0 \s-1API\s0 functions are affected by the use
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of \fB\s-1ENGINE\s0\fR \s-1API\s0 calls.
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.PP
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Initially, the default \s-1DH_METHOD\s0 is the OpenSSL internal implementation, as
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returned by \fIDH_OpenSSL()\fR.
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.PP
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\&\fIDH_set_default_method()\fR makes \fBmeth\fR the default method for all \s-1DH\s0
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structures created later. \fB\s-1NB\s0\fR: This is true only whilst no \s-1ENGINE\s0 has been set
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as a default for \s-1DH\s0, so this function is no longer recommended.
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.PP
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\&\fIDH_get_default_method()\fR returns a pointer to the current default \s-1DH_METHOD\s0.
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However, the meaningfulness of this result is dependant on whether the \s-1ENGINE\s0
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\&\s-1API\s0 is being used, so this function is no longer recommended.
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.PP
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\&\fIDH_set_method()\fR selects \fBmeth\fR to perform all operations using the key \fBdh\fR.
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This will replace the \s-1DH_METHOD\s0 used by the \s-1DH\s0 key and if the previous method
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was supplied by an \s-1ENGINE\s0, the handle to that \s-1ENGINE\s0 will be released during the
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change. It is possible to have \s-1DH\s0 keys that only work with certain \s-1DH_METHOD\s0
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implementations (eg. from an \s-1ENGINE\s0 module that supports embedded
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hardware-protected keys), and in such cases attempting to change the \s-1DH_METHOD\s0
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for the key can have unexpected results.
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.PP
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\&\fIDH_new_method()\fR allocates and initializes a \s-1DH\s0 structure so that \fBengine\fR will
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be used for the \s-1DH\s0 operations. If \fBengine\fR is \s-1NULL\s0, the default \s-1ENGINE\s0 for \s-1DH\s0
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operations is used, and if no default \s-1ENGINE\s0 is set, the \s-1DH_METHOD\s0 controlled by
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\&\fIDH_set_default_method()\fR is used.
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.SH "THE DH_METHOD STRUCTURE"
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.IX Header "THE DH_METHOD STRUCTURE"
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.Vb 4
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\& typedef struct dh_meth_st
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\& {
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\& /* name of the implementation */
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\& const char *name;
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.Ve
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.Vb 2
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\& /* generate private and public DH values for key agreement */
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\& int (*generate_key)(DH *dh);
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.Ve
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.Vb 2
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\& /* compute shared secret */
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\& int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh);
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.Ve
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.Vb 4
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\& /* compute r = a ^ p mod m (May be NULL for some implementations) */
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\& int (*bn_mod_exp)(DH *dh, BIGNUM *r, BIGNUM *a, const BIGNUM *p,
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\& const BIGNUM *m, BN_CTX *ctx,
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\& BN_MONT_CTX *m_ctx);
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.Ve
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.Vb 2
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\& /* called at DH_new */
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\& int (*init)(DH *dh);
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.Ve
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.Vb 2
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\& /* called at DH_free */
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\& int (*finish)(DH *dh);
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.Ve
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.Vb 1
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\& int flags;
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.Ve
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.Vb 1
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\& char *app_data; /* ?? */
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.Ve
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.Vb 1
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\& } DH_METHOD;
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.Ve
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIDH_OpenSSL()\fR and \fIDH_get_default_method()\fR return pointers to the respective
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\&\fB\s-1DH_METHOD\s0\fRs.
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.PP
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\&\fIDH_set_default_method()\fR returns no value.
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.PP
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\&\fIDH_set_method()\fR returns non-zero if the provided \fBmeth\fR was successfully set as
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the method for \fBdh\fR (including unloading the \s-1ENGINE\s0 handle if the previous
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method was supplied by an \s-1ENGINE\s0).
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.PP
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\&\fIDH_new_method()\fR returns \s-1NULL\s0 and sets an error code that can be obtained by
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ERR_get_error(3) if the allocation fails. Otherwise it
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returns a pointer to the newly allocated structure.
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.SH "NOTES"
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.IX Header "NOTES"
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As of version 0.9.7, \s-1DH_METHOD\s0 implementations are grouped together with other
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algorithmic APIs (eg. \s-1RSA_METHOD\s0, \s-1EVP_CIPHER\s0, etc) in \fB\s-1ENGINE\s0\fR modules. If a
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default \s-1ENGINE\s0 is specified for \s-1DH\s0 functionality using an \s-1ENGINE\s0 \s-1API\s0 function,
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that will override any \s-1DH\s0 defaults set using the \s-1DH\s0 \s-1API\s0 (ie.
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\&\fIDH_set_default_method()\fR). For this reason, the \s-1ENGINE\s0 \s-1API\s0 is the recommended way
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to control default implementations for use in \s-1DH\s0 and other cryptographic
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algorithms.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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openssl_dh(3), DH_new(3)
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\fIDH_set_default_method()\fR, \fIDH_get_default_method()\fR, \fIDH_set_method()\fR,
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\&\fIDH_new_method()\fR and \fIDH_OpenSSL()\fR were added in OpenSSL 0.9.4.
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.PP
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\&\fIDH_set_default_openssl_method()\fR and \fIDH_get_default_openssl_method()\fR replaced
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\&\fIDH_set_default_method()\fR and \fIDH_get_default_method()\fR respectively, and
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\&\fIDH_set_method()\fR and \fIDH_new_method()\fR were altered to use \fB\s-1ENGINE\s0\fRs rather than
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\&\fB\s-1DH_METHOD\s0\fRs during development of the engine version of OpenSSL 0.9.6. For
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0.9.7, the handling of defaults in the \s-1ENGINE\s0 \s-1API\s0 was restructured so that this
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change was reversed, and behaviour of the other functions resembled more closely
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the previous behaviour. The behaviour of defaults in the \s-1ENGINE\s0 \s-1API\s0 now
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transparently overrides the behaviour of defaults in the \s-1DH\s0 \s-1API\s0 without
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requiring changing these function prototypes.
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