NAME

OSSL_PARAM_allocate_from_text - OSSL_PARAM construction utilities

SYNOPSIS

 #include <openssl/params.h>

 int OSSL_PARAM_allocate_from_text(OSSL_PARAM *to,
                                   const OSSL_PARAM *paramdefs,
                                   const char *key, const char *value,
                                   size_t value_n,
                                   int *found);

DESCRIPTION

With OpenSSL before version 3.0, parameters were passed down to or retrieved from algorithm implementations via control functions. Some of these control functions existed in variants that took string parameters, for example OSSL_PARAM(3) for more information).

OSSL_PARAM_allocate_from_text() takes a control key, value and value size value_n, and given a parameter descriptor array paramdefs, it converts the value to something suitable for RETURN VALUES

OSSL_PARAM_allocate_from_text() returns 1 on success, and 0 on error.

NOTES

The parameter descriptor array comes from functions dedicated to return them. The following OSSL_PARAM attributes are used:

key
data
data_size

All other attributes are ignored.

The data_size attribute can be zero, meaning that the parameter it describes expects arbitrary length data.

EXAMPLES

Code that looked like this:

  int mac_ctrl_string(EVP_PKEY_CTX *ctx, const char *value)
  {
      int rv;
      char *stmp, *vtmp = NULL;

      stmp = OPENSSL_strdup(value);
      if (stmp == NULL)
          return -1;
      vtmp = strchr(stmp, ':');
      if (vtmp != NULL)
          *vtmp++ = '\0';
      rv = EVP_MAC_ctrl_str(ctx, stmp, vtmp);
      OPENSSL_free(stmp);
      return rv;
  }

  ...


  for (i = 0; i < sk_OPENSSL_STRING_num(macopts); i++) {
      char *macopt = sk_OPENSSL_STRING_value(macopts, i);

      if (pkey_ctrl_string(mac_ctx, macopt) <= 0) {
          BIO_printf(bio_err,
                     "MAC parameter error \"%s\"\n", macopt);
          ERR_print_errors(bio_err);
          goto mac_end;
      }
  }

Can be written like this instead:

  OSSL_PARAM *params =
      OPENSSL_zalloc(sizeof(*params)
                     * (sk_OPENSSL_STRING_num(opts) + 1));
  const OSSL_PARAM *paramdefs = EVP_MAC_settable_ctx_params(mac);
  size_t params_n;
  char *opt = "<unknown>";

  for (params_n = 0; params_n < (size_t)sk_OPENSSL_STRING_num(opts);
       params_n++) {
      char *stmp, *vtmp = NULL;

      opt = sk_OPENSSL_STRING_value(opts, (int)params_n);
      if ((stmp = OPENSSL_strdup(opt)) == NULL
              || (vtmp = strchr(stmp, ':')) == NULL)
          goto err;

      *vtmp++ = '\0';
      if (!OSSL_PARAM_allocate_from_text(&params[params_n],
                                         paramdefs, stmp,
                                         vtmp, strlen(vtmp), NULL))
          goto err;
  }
  params[params_n] = OSSL_PARAM_construct_end();
  if (!EVP_MAC_CTX_set_params(ctx, params))
      goto err;
  while (params_n-- > 0)
      OPENSSL_free(params[params_n].data);
  OPENSSL_free(params);
  /* ... */
  return;

 err:
  BIO_printf(bio_err, "MAC parameter error '%s'\n", opt);
  ERR_print_errors(bio_err);

COPYRIGHT