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Package containing this man page: core/openssl (version 1.1.0.f-2)

DH_GENERATE_PARAMETERS(3) OpenSSL DH_GENERATE_PARAMETERS(3)

NAME

DH_generate_parameters_ex, DH_generate_parameters, DH_check, DH_check_params - generate and check Diffie-Hellman parameters

SYNOPSIS

 #include <openssl/dh.h>
 int DH_generate_parameters_ex(DH *dh, int prime_len, int generator, BN_GENCB *cb);
 int DH_check(DH *dh, int *codes);
 int DH_check_params(DH *dh, int *codes);
Deprecated:
 #if OPENSSL_API_COMPAT < 0x00908000L
 DH *DH_generate_parameters(int prime_len, int generator,
     void (*callback)(int, int, void *), void *cb_arg);
 #endif

DESCRIPTION

DH_generate_parameters_ex() generates Diffie-Hellman parameters that can be shared among a group of users, and stores them in the provided DH structure. The pseudo-random number generator must be seeded prior to calling DH_generate_parameters().
prime_len is the length in bits of the safe prime to be generated. generator is a small number > 1, typically 2 or 5.
A callback function may be used to provide feedback about the progress of the key generation. If cb is not NULL, it will be called as described in BN_generate_prime(3) while a random prime number is generated, and when a prime has been found, BN_GENCB_call(cb, 3, 0) is called. See BN_generate_prime(3) for information on the BN_GENCB_call() function.
DH_check_params() confirms that the p and g are likely enough to be valid. This is a lightweight check, if a more thorough check is needed, use DH_check(). The value of *codes is updated with any problems found. If *codes is zero then no problems were found, otherwise the following bits may be set:
DH_CHECK_P_NOT_PRIME
The parameter p has been determined to not being an odd prime. Note that the lack of this bit doesn't guarantee that p is a prime.
DH_NOT_SUITABLE_GENERATOR
The generator g is not suitable. Note that the lack of this bit doesn't guarantee that g is suitable, unless p is known to be a strong prime.
DH_check() confirms that the Diffie-Hellman parameters dh are valid. The value of *codes is updated with any problems found. If *codes is zero then no problems were found, otherwise the following bits may be set:
DH_CHECK_P_NOT_PRIME
The parameter p is not prime.
DH_CHECK_P_NOT_SAFE_PRIME
The parameter p is not a safe prime and no q value is present.
DH_UNABLE_TO_CHECK_GENERATOR
The generator g cannot be checked for suitability.
DH_NOT_SUITABLE_GENERATOR
The generator g is not suitable.
DH_CHECK_Q_NOT_PRIME
The parameter q is not prime.
DH_CHECK_INVALID_Q_VALUE
The parameter q is invalid.
DH_CHECK_INVALID_J_VALUE
The parameter j is invalid.

RETURN VALUES

DH_generate_parameters_ex(), DH_check() and DH_check_params() return 1 if the check could be performed, 0 otherwise.
DH_generate_parameters() (deprecated) returns a pointer to the DH structure, or NULL if the parameter generation fails.
The error codes can be obtained by ERR_get_error(3).

NOTES

DH_generate_parameters_ex() and DH_generate_parameters() may run for several hours before finding a suitable prime.
The parameters generated by DH_generate_parameters_ex() and DH_generate_parameters() are not to be used in signature schemes.

SEE ALSO

DH_new(3), ERR_get_error(3), RAND_bytes(3), DH_free(3)

COPYRIGHT

Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.
2017-05-25 1.1.0f