Ubuntu Manpage: DH_generate_parameters_ex, DH_generate_parameters, DH_check, DH_check_params, DH_check

Provided by: libssl-doc_1.1.1-1ubuntu2.1~18.04.23_all

NAME

       DH_generate_parameters_ex, DH_generate_parameters, DH_check, DH_check_params, DH_check_ex,
       DH_check_params_ex, DH_check_pub_key_ex - 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);

        int DH_check_ex(const DH *dh);
        int DH_check_params_ex(const DH *dh);
        int DH_check_pub_key_ex(const DH *dh, const BIGNUM *pub_key);

       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
before calling it. The parameters generated by DH_generate_parameters_ex() should not be used in
signature schemes.

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_ex(3) for information on the BN_GENCB_call() function.

DH_generate_parameters() is similar to DH_generate_prime_ex() but expects an old-style callback function;
see BN_generate_prime(3) for information on the old-style callback.

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.

DH_check_ex(), DH_check_params() and DH_check_pub_key_ex() are similar to DH_check() and
DH_check_params() respectively, but the error reasons are added to the thread's error queue instead of
provided as return values from the function.

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() returns a pointer to the DH structure or NULL if the parameter generation fails.

       DH_check_ex(), DH_check_params() and DH_check_pub_key_ex() return 1 if the check is successful, 0 for
       failed.

       The error codes can be obtained by ERR_get_error(3).

HISTORY

       DH_generate_parameters() was deprecated in OpenSSL 0.9.8; use DH_generate_parameters_ex() instead.

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