DH_generate_parameters3ssl

Usage

 #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);

 DH *DH_generate_parameters(int prime_len, int generator,
                            void (*callback)(int, int, void *), void *cb_arg);

Overview

All of the functions described on this page are deprecated. Applications should instead use EVP_PKEY_check(3), EVP_PKEY_public_check(3), EVP_PKEY_private_check(3) and EVP_PKEY_param_check(3).

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_MODULUS_TOO_SMALL

The modulus is too small.

DH_MODULUS_TOO_LARGE

The modulus is too large.

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:

If 0 is returned or *codes is set to a nonzero value the supplied parameters should not be used for Diffie-Hellman operations otherwise the security properties of the key exchange are not guaranteed.

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).