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1 .\" $OpenBSD: DH_generate_parameters.3,v 1.6 2016/12/10 22:22:59 schwarze Exp $
2 .\" OpenSSL 05ea606a May 20 20:52:46 2016 -0400
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51 .Dd $Mdocdate: December 10 2016 $
52 .Dt DH_GENERATE_PARAMETERS 3
53 .Os
54 .Sh NAME
55 .Nm DH_generate_parameters_ex ,
56 .Nm DH_check ,
57 .Nm DH_generate_parameters
58 .Nd generate and check Diffie-Hellman parameters
59 .Sh SYNOPSIS
60 .In openssl/dh.h
61 .Ft int
62 .Fo DH_generate_parameters_ex
63 .Fa "DH *dh"
64 .Fa "int prime_len"
65 .Fa "int generator"
66 .Fa "BN_GENCB *cb"
67 .Fc
68 .Ft int
69 .Fo DH_check
70 .Fa "DH *dh"
71 .Fa "int *codes"
72 .Fc
73 .Pp
74 Deprecated:
75 .Pp
76 .Ft DH *
77 .Fo DH_generate_parameters
78 .Fa "int prime_len"
79 .Fa "int generator"
80 .Fa "void (*callback)(int"
81 .Fa int
82 .Fa "void *)"
83 .Fa "void *cb_arg"
84 .Fc
85 .Sh DESCRIPTION
86 .Fn DH_generate_parameters_ex
87 generates Diffie-Hellman parameters that can be shared among a group of
88 users, and stores them in the provided
89 .Vt DH
90 structure.
91 .Pp
92 .Fa prime_len
93 is the length in bits of the safe prime to be generated.
94 .Fa generator
95 is a small number > 1, typically 2 or 5.
96 .Pp
97 A callback function may be used to provide feedback about the progress
98 of the key generation.
99 If
100 .Fa cb
101 is not
102 .Dv NULL ,
103 it will be called as described in
104 .Xr BN_generate_prime 3
105 while a random prime number is generated, and when a prime has been
106 found,
107 .Fn BN_GENCB_call cb 3 0
108 is called; see
109 .Xr BN_GENCB_call 3 .
110 .Pp
111 .Fn DH_check
112 validates Diffie-Hellman parameters.
113 If no problems are found,
114 .Pf * Ar codes
115 is set to zero.
116 Otherwise, one or more of the following bits are set:
117 .Bl -tag -width Ds
118 .It Dv DH_CHECK_P_NOT_PRIME
119 The parameter
120 .Fa dh->p
121 is not prime.
122 .It Dv DH_CHECK_P_NOT_SAFE_PRIME
123 The parameter
124 .Fa dh->p
125 is not a safe prime.
126 .It Dv DH_UNABLE_TO_CHECK_GENERATOR
127 The generator
128 .Fa dh->g
129 cannot be checked for suitability: it is neither 2 nor 5.
130 .It Dv DH_NOT_SUITABLE_GENERATOR
131 The generator
132 .Fa dh->g
133 is not suitable.
134 .El
135 .Sh RETURN VALUES
136 .Fn DH_generate_parameters_ex
137 and
138 .Fn DH_check
139 return 1 if the check could be performed, or 0 otherwise.
140 .Pp
141 .Fn DH_generate_parameters
142 (deprecated) returns a pointer to the
143 .Vt DH
144 structure, or
145 .Dv NULL
146 if the parameter generation fails.
147 .Pp
148 The error codes can be obtained by
149 .Xr ERR_get_error 3 .
150 .Sh SEE ALSO
151 .Xr DH_new 3 ,
152 .Xr ERR_get_error 3 ,
153 .Xr RAND_bytes 3
154 .Sh HISTORY
155 .Fn DH_check
156 is available in all versions of SSLeay and OpenSSL.
157 The
158 .Fa cb_arg
159 argument to
160 .Fn DH_generate_parameters
161 was added in SSLeay 0.9.0.
162 .Pp
163 In versions before OpenSSL 0.9.5,
164 .Dv DH_CHECK_P_NOT_STRONG_PRIME
165 is used instead of
166 .Dv DH_CHECK_P_NOT_SAFE_PRIME .
167 .Sh CAVEATS
168 .Fn DH_generate_parameters_ex
169 and
170 .Fn DH_generate_parameters
171 may run for several hours before finding a suitable prime.
172 .Pp
173 The parameters generated by
174 .Fn DH_generate_parameters_ex
175 and
176 .Fn DH_generate_parameters
177 are not to be used in signature schemes.
178 .Sh BUGS
179 If
180 .Fa generator
181 is not 2 or 5,
182 .Fa dh->g Ns = Ns Fa generator
183 is not a usable generator.