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DH_generate_parameters(3)
NAME
  DH_generate_parameters, DH_check - Generate and check Diffie-Hellman
  parameters

SYNOPSIS
  #include <openssl/dh.h>

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

  int DH_check(
	  DH *dh, int *codes );

DESCRIPTION
  The DH_generate_parameters() function generates Diffie-Hellman parameters
  that can be shared among a group of users, and returns them in a newly
  allocated DH structure. The pseudo-random number generator must be seeded
  prior to calling DH_generate_parameters().

  The prime_len is the length in bits of the safe prime to be generated. The
  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 callback is not NULL, it will be called as described
  in BN_generate_prime() while a random prime number is generated, and when a
  prime has been found, callback(3, 0, cb_arg) is called.

  DH_check() validates Diffie-Hellman parameters. It checks that p is a safe
  prime, and that g is a suitable generator. In the case of an error, the bit
  flags DH_CHECK_P_NOT_SAFE_PRIME or DH_NOT_SUITABLE_GENERATOR are set in
  *codes.  DH_UNABLE_TO_CHECK_GENERATOR is set if the generator cannot be
  checked, meaning it does not equal 2 or 5.

NOTES
  The DH_generate_parameters() function may run for several hours before
  finding a suitable prime.

  The parameters generated by DH_generate_parameters() are not to be used in
  signature schemes.

RESTRICTIONS
  If generator is not 2 or 5, dh->g=generator is not a usable generator.

RETURN VALUES
  The DH_generate_parameters() function returns a pointer to the DH
  structure, or NULL if the parameter generation fails. The error codes can
  be obtained from ERR_get_error().

  The DH_check() function returns 1 if the check could be performed, 0
  otherwise.

HISTORY
  The DH_check() function is available in all versions of SSLeay and OpenSSL.
  The cb_arg argument to DH_generate_parameters() was added in SSLeay 0.9.0.

  In versions before OpenSSL 0.9.5, DH_CHECK_P_NOT_STRONG_PRIME is used
  instead of DH_CHECK_P_NOT_SAFE_PRIME.

SEE ALSO
  Functions: dh(3), err(3), rand(3), DH_free(3)

Index for Section 3

Alphabetical listing for D

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