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>.