DHPARAM(1) OpenSSL DHPARAM(1) NNAAMMEE dhparam - DH parameter manipulation and generation SSYYNNOOPPSSIISS ooppeennssssll ddhhppaarraamm [--iinnffoorrmm DDEERR||PPEEMM] [--oouuttffoorrmm DDEERR||PPEEMM] [--iinn _f_i_l_e_n_a_m_e] [--oouutt _f_i_l_e_n_a_m_e] [--ddssaappaarraamm] [--cchheecckk] [--nnoooouutt] [--tteexxtt] [--CC] [--22] [--55] [--rraanndd _f_i_l_e_(_s_)] [--eennggiinnee iidd] [_n_u_m_b_i_t_s] DDEESSCCRRIIPPTTIIOONN This command is used to manipulate DH parameter files. OOPPTTIIOONNSS --iinnffoorrmm DDEERR||PPEEMM This specifies the input format. The DDEERR option uses an ASN1 DER encoded form compatible with the PKCS#3 DHparameter structure. The PEM form is the default format: it consists of the DDEERR format base64 encoded with additional header and footer lines. --oouuttffoorrmm DDEERR||PPEEMM This specifies the output format, the options have the same meaning as the --iinnffoorrmm option. --iinn _f_i_l_e_n_a_m_e This specifies the input filename to read parameters from or stan- dard input if this option is not specified. --oouutt _f_i_l_e_n_a_m_e This specifies the output filename parameters to. Standard output is used if this option is not present. The output filename should nnoott be the same as the input filename. --ddssaappaarraamm If this option is used, DSA rather than DH parameters are read or created; they are converted to DH format. Otherwise, "strong" primes (such that (p-1)/2 is also prime) will be used for DH param- eter generation. DH parameter generation with the --ddssaappaarraamm option is much faster, and the recommended exponent length is shorter, which makes DH key exchange more efficient. Beware that with such DSA-style DH param- eters, a fresh DH key should be created for each use to avoid small-subgroup attacks that may be possible otherwise. --cchheecckk check if the parameters are valid primes and generator. --22, --55 The generator to use, either 2 or 5. If present then the input file is ignored and parameters are generated instead. If not present but nnuummbbiittss is present, parameters are generated with the default gen- erator 2. --rraanndd _f_i_l_e_(_s_) a file or files containing random data used to seed the random num- ber generator, or an EGD socket (see _R_A_N_D___e_g_d(3)). Multiple files can be specified separated by a OS-dependent character. The sepa- rator is ;; for MS-Windows, ,, for OpenVMS, and :: for all others. _n_u_m_b_i_t_s this option specifies that a parameter set should be generated of size _n_u_m_b_i_t_s. It must be the last option. If this option is present then the input file is ignored and parameters are generated instead. If this option is not present but a generator (--22 or --55) is present, parameters are generated with a default length of 2048 bits. --nnoooouutt this option inhibits the output of the encoded version of the parameters. --tteexxtt this option prints out the DH parameters in human readable form. --CC this option converts the parameters into C code. The parameters can then be loaded by calling the ggeett__ddhh_n_u_m_b_i_t_s(()) function. --eennggiinnee iidd specifying an engine (by its unique iidd string) will cause ddhhppaarraamm to attempt to obtain a functional reference to the specified engine, thus initialising it if needed. The engine will then be set as the default for all available algorithms. WWAARRNNIINNGGSS The program ddhhppaarraamm combines the functionality of the programs ddhh and ggeennddhh in previous versions of OpenSSL and SSLeay. The ddhh and ggeennddhh pro- grams are retained for now but may have different purposes in future versions of OpenSSL. NNOOTTEESS PEM format DH parameters use the header and footer lines: -----BEGIN DH PARAMETERS----- -----END DH PARAMETERS----- OpenSSL currently only supports the older PKCS#3 DH, not the newer X9.42 DH. This program manipulates DH parameters not keys. BBUUGGSS There should be a way to generate and manipulate DH keys. SSEEEE AALLSSOO _d_s_a_p_a_r_a_m(1) HHIISSTTOORRYY The ddhhppaarraamm command was added in OpenSSL 0.9.5. The --ddssaappaarraamm option was added in OpenSSL 0.9.6. 1.0.1u 2016-09-22 DHPARAM(1)