text: /* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
  /* lib/gssapi/krb5/prf.c */
  /*
   * Copyright 2009 by the Massachusetts Institute of Technology.
   * All Rights Reserved.
   *
   * Export of this software from the United States of America may
   *   require a specific license from the United States Government.
   *   It is the responsibility of any person or organization contemplating
   *   export to obtain such a license before exporting.
   *
   * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
   * distribute this software and its documentation for any purpose and
   * without fee is hereby granted, provided that the above copyright
   * notice appear in all copies and that both that copyright notice and
   * this permission notice appear in supporting documentation, and that
   * the name of M.I.T. not be used in advertising or publicity pertaining
   * to distribution of the software without specific, written prior
   * permission.  Furthermore if you modify this software you must label
   * your software as modified software and not distribute it in such a
   * fashion that it might be confused with the original M.I.T. software.
   * M.I.T. makes no representations about the suitability of
   * this software for any purpose.  It is provided "as is" without express
   * or implied warranty.
   */
  
  #include "gssapiP_krb5.h"
  #include "k5-int.h"
  
  #ifndef MIN /* Usually found in <sys/param.h>. */
  #define MIN(_a, _b) ((_a) < (_b) ? (_a) : (_b))
  #endif
  
  OM_uint32 KRB5_CALLCONV krb5_gss_pseudo_random(
      OM_uint32* minor_status, gss_ctx_id_t context, int prf_key,
      const gss_buffer_t prf_in, ssize_t desired_output_len, gss_buffer_t prf_out)
  {
      krb5_error_code code;
      krb5_key key = NULL;
      krb5_gss_ctx_id_t ctx;
      int i;
      OM_uint32 minor;
      size_t prflen;
      krb5_data t, ns;
      unsigned char* p;
  
      prf_out->length = 0;
      prf_out->value = NULL;
  
      t.length = 0;
      t.data = NULL;
  
      ns.length = 0;
      ns.data = NULL;
  
      ctx = (krb5_gss_ctx_id_t)context;
      if (ctx->terminated || !ctx->established)
      {
          *minor_status = KG_CTX_INCOMPLETE;
          return GSS_S_NO_CONTEXT;
      }
  
      switch (prf_key)
      {
          case GSS_C_PRF_KEY_FULL:
              if (ctx->have_acceptor_subkey)
              {
                  key = ctx->acceptor_subkey;
                  break;
              }
              /* fallthrough */
          case GSS_C_PRF_KEY_PARTIAL:
              key = ctx->subkey;
              break;
          default:
              code = EINVAL;
              goto cleanup;
      }
  
      if (key == NULL)
      {
          code = EINVAL;
          goto cleanup;
      }
  
      if (desired_output_len == 0)
          return GSS_S_COMPLETE;
  
      prf_out->value = k5alloc(desired_output_len, &code);
      if (prf_out->value == NULL)
      {
          code = KG_INPUT_TOO_LONG;
          goto cleanup;
      }
      prf_out->length = desired_output_len;
  
      code = krb5_c_prf_length(ctx->k5_context,
                               krb5_k_key_enctype(ctx->k5_context, key), &prflen);
      if (code != 0)
          goto cleanup;
  
      ns.length = 4 + prf_in->length;
      ns.data = k5alloc(ns.length, &code);
      if (ns.data == NULL)
      {
          code = KG_INPUT_TOO_LONG;
          goto cleanup;
      }
  
      t.length = prflen;
      t.data = k5alloc(t.length, &code);
      if (t.data == NULL)
          goto cleanup;
  
      memcpy(ns.data + 4, prf_in->value, prf_in->length);
      i = 0;
      p = (unsigned char*)prf_out->value;
      while (desired_output_len > 0)
      {
          store_32_be(i, ns.data);
  
          code = krb5_k_prf(ctx->k5_context, key, &ns, &t);
          if (code != 0)
              goto cleanup;
  
          memcpy(p, t.data, MIN(t.length, desired_output_len));
  
          p += t.length;
          desired_output_len -= t.length;
          i++;
      }
  
  cleanup:
      if (code != 0)
          gss_release_buffer(&minor, prf_out);
      krb5_free_data_contents(ctx->k5_context, &ns);
      krb5_free_data_contents(ctx->k5_context, &t);
  
      *minor_status = (OM_uint32)code;
      return (code == 0) ? GSS_S_COMPLETE : GSS_S_FAILURE;
  }
  