.\" $OpenBSD: DH_generate_parameters.3,v 1.14 2022/07/13 13:47:59 schwarze Exp $ .\" full merge up to: OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100 .\" selective merge up to: OpenSSL b0edda11 Mar 20 13:00:17 2018 +0000 .\" .\" This file is a derived work. .\" The changes are covered by the following Copyright and license: .\" .\" Copyright (c) 2022 Ingo Schwarze .\" .\" Permission to use, copy, modify, and distribute this software for any .\" purpose with or without fee is hereby granted, provided that the above .\" copyright notice and this permission notice appear in all copies. .\" .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: July 13 2022 $ .Dt DH_GENERATE_PARAMETERS 3 .Os .Sh NAME .Nm DH_generate_parameters_ex , .Nm DH_check , .Nm DH_check_pub_key , .Nm DH_generate_parameters .Nd generate and check Diffie-Hellman parameters .Sh SYNOPSIS .In openssl/dh.h .Ft int .Fo DH_generate_parameters_ex .Fa "DH *dh" .Fa "int prime_len" .Fa "int generator" .Fa "BN_GENCB *cb" .Fc .Ft int .Fo DH_check .Fa "DH *dh" .Fa "int *codes" .Fc .Ft int .Fo DH_check_pub_key .Fa "const DH *dh" .Fa "const BIGNUM *pub_key" .Fa "int *codes" .Fc .Pp Deprecated: .Pp .Ft DH * .Fo DH_generate_parameters .Fa "int prime_len" .Fa "int generator" .Fa "void (*callback)(int, int, void *)" .Fa "void *cb_arg" .Fc .Sh DESCRIPTION .Fn DH_generate_parameters_ex generates Diffie-Hellman parameters that can be shared among a group of users, and stores them in the provided .Vt DH structure. .Pp .Fa prime_len is the length in bits of the safe prime to be generated. .Fa generator is a small number > 1, typically 2 or 5. .Pp A callback function may be used to provide feedback about the progress of the key generation. If .Fa cb is not .Dv NULL , it will be called as described in .Xr BN_generate_prime 3 while a random prime number is generated, and when a prime has been found, .Fn BN_GENCB_call cb 3 0 is called; see .Xr BN_GENCB_call 3 . .Pp .Fn DH_check validates Diffie-Hellman parameters. If no problems are found, .Pf * Ar codes is set to zero. Otherwise, one or more of the following bits are set: .Bl -tag -width Ds .It Dv DH_CHECK_P_NOT_PRIME The parameter .Fa dh->p is not prime. .It Dv DH_CHECK_P_NOT_SAFE_PRIME The parameter .Fa dh->p is not a safe prime. .It Dv DH_UNABLE_TO_CHECK_GENERATOR The generator .Fa dh->g cannot be checked for suitability: it is neither 2 nor 5. .It Dv DH_NOT_SUITABLE_GENERATOR The generator .Fa dh->g is not suitable. .El .Pp .Fn DH_check_pub_key checks whether .Fa pub_key is a valid public key when using the domain parameters contained in .Fa dh . If no problems are found, .Pf * Ar codes is set to zero. Otherwise, one or more of the following bits are set: .Bl -tag -width Ds .It Dv DH_CHECK_PUBKEY_TOO_SMALL .Fa pub_key is less than or equal to 1. .It Dv DH_CHECK_PUBKEY_TOO_LARGE .Fa pub_key is greater than or equal to .Fa dh->p No \- 1 . .It DH_CHECK_PUBKEY_INVALID .Fa dh->q is set but .Fa pub_key to the power of .Fa dh->q is not 1 modulo .Fa dh->p . .El .Sh RETURN VALUES .Fn DH_generate_parameters_ex , .Fn DH_check , and .Fn DH_check_pub_key return 1 if the check could be performed or 0 otherwise. .Pp .Fn DH_generate_parameters (deprecated) returns a pointer to the .Vt DH structure, or .Dv NULL if the parameter generation fails. .Pp The error codes can be obtained by .Xr ERR_get_error 3 . .Sh SEE ALSO .Xr DH_get0_pqg 3 , .Xr DH_new 3 .Sh HISTORY .Fn DH_check and .Fn DH_generate_parameters first appeared in SSLeay 0.5.1 and have been available since .Ox 2.4 . .Pp The .Fa cb_arg argument to .Fn DH_generate_parameters was added in SSLeay 0.9.0. .Pp .Fn DH_check_pub_key first appeared in OpenSSL 0.9.8a and has been available since .Ox 4.0 . .Pp .Fn DH_generate_parameters_ex first appeared in OpenSSL 0.9.8 and has been available since .Ox 4.5 . .Sh CAVEATS .Fn DH_generate_parameters_ex and .Fn DH_generate_parameters may run for several hours before finding a suitable prime. .Pp The parameters generated by .Fn DH_generate_parameters_ex and .Fn DH_generate_parameters are not to be used in signature schemes. .Sh BUGS If .Fa generator is not 2 or 5, .Fa dh->g Ns = Ns Fa generator is not a usable generator.