text: ﻿/**
   *  \brief HAVEGE: HArdware Volatile Entropy Gathering and Expansion
   *
   *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
   *  SPDX-License-Identifier: Apache-2.0
   *
   *  Licensed under the Apache License, Version 2.0 (the "License"); you may
   *  not use this file except in compliance with the License.
   *  You may obtain a copy of the License at
   *
   *  http://www.apache.org/licenses/LICENSE-2.0
   *
   *  Unless required by applicable law or agreed to in writing, software
   *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   *  See the License for the specific language governing permissions and
   *  limitations under the License.
   *
   *  This file is part of mbed TLS (https://tls.mbed.org)
   */
  /*
   *  The HAVEGE RNG was designed by Andre Seznec in 2002.
   *
   *  http://www.irisa.fr/caps/projects/hipsor/publi.php
   *
   *  Contact: seznec(at)irisa_dot_fr - orocheco(at)irisa_dot_fr
   */
  
  #if !defined(MBEDTLS_CONFIG_FILE)
  #include "mbedtls/config.h"
  #else
  #include MBEDTLS_CONFIG_FILE
  #endif
  
  #if defined(MBEDTLS_HAVEGE_C)
  
  #include "mbedtls/havege.h"
  #include "mbedtls/timing.h"
  #include "mbedtls/platform_util.h"
  
  #include <string.h>
  
  /* ------------------------------------------------------------------------
   * On average, one iteration accesses two 8-word blocks in the havege WALK
   * table, and generates 16 words in the RES array.
   *
   * The data read in the WALK table is updated and permuted after each use.
   * The result of the hardware clock counter read is used  for this update.
   *
   * 25 conditional tests are present.  The conditional tests are grouped in
   * two nested  groups of 12 conditional tests and 1 test that controls the
   * permutation; on average, there should be 6 tests executed and 3 of them
   * should be mispredicted.
   * ------------------------------------------------------------------------
   */
  
  #define SWAP(X,Y) { int *T = X; X = Y; Y = T; }
  
  #define TST1_ENTER if( PTEST & 1 ) { PTEST ^= 3; PTEST >>= 1;
  #define TST2_ENTER if( PTEST & 1 ) { PTEST ^= 3; PTEST >>= 1;
  
  #define TST1_LEAVE U1++; }
  #define TST2_LEAVE U2++; }
  
  #define ONE_ITERATION                                   \
                                                          \
      PTEST = PT1 >> 20;                                  \
                                                          \
      TST1_ENTER  TST1_ENTER  TST1_ENTER  TST1_ENTER      \
      TST1_ENTER  TST1_ENTER  TST1_ENTER  TST1_ENTER      \
      TST1_ENTER  TST1_ENTER  TST1_ENTER  TST1_ENTER      \
                                                          \
      TST1_LEAVE  TST1_LEAVE  TST1_LEAVE  TST1_LEAVE      \
      TST1_LEAVE  TST1_LEAVE  TST1_LEAVE  TST1_LEAVE      \
      TST1_LEAVE  TST1_LEAVE  TST1_LEAVE  TST1_LEAVE      \
                                                          \
      PTX = (PT1 >> 18) & 7;                              \
      PT1 &= 0x1FFF;                                      \
      PT2 &= 0x1FFF;                                      \
      CLK = (int) mbedtls_timing_hardclock();                            \
                                                          \
      i = 0;                                              \
      A = &WALK[PT1    ]; RES[i++] ^= *A;                 \
      B = &WALK[PT2    ]; RES[i++] ^= *B;                 \
      C = &WALK[PT1 ^ 1]; RES[i++] ^= *C;                 \
      D = &WALK[PT2 ^ 4]; RES[i++] ^= *D;                 \
                                                          \
      IN = (*A >> (1)) ^ (*A << (31)) ^ CLK;              \
      *A = (*B >> (2)) ^ (*B << (30)) ^ CLK;              \
      *B = IN ^ U1;                                       \
      *C = (*C >> (3)) ^ (*C << (29)) ^ CLK;              \
      *D = (*D >> (4)) ^ (*D << (28)) ^ CLK;              \
                                                          \
      A = &WALK[PT1 ^ 2]; RES[i++] ^= *A;                 \
      B = &WALK[PT2 ^ 2]; RES[i++] ^= *B;                 \
      C = &WALK[PT1 ^ 3]; RES[i++] ^= *C;                 \
      D = &WALK[PT2 ^ 6]; RES[i++] ^= *D;                 \
                                                          \
      if( PTEST & 1 ) SWAP( A, C );                       \
                                                          \
      IN = (*A >> (5)) ^ (*A << (27)) ^ CLK;              \
      *A = (*B >> (6)) ^ (*B << (26)) ^ CLK;              \
      *B = IN; CLK = (int) mbedtls_timing_hardclock();                   \
      *C = (*C >> (7)) ^ (*C << (25)) ^ CLK;              \
      *D = (*D >> (8)) ^ (*D << (24)) ^ CLK;              \
                                                          \
      A = &WALK[PT1 ^ 4];                                 \
      B = &WALK[PT2 ^ 1];                                 \
                                                          \
      PTEST = PT2 >> 1;                                   \
                                                          \
      PT2 = (RES[(i - 8) ^ PTY] ^ WALK[PT2 ^ PTY ^ 7]);   \
      PT2 = ((PT2 & 0x1FFF) & (~8)) ^ ((PT1 ^ 8) & 0x8);  \
      PTY = (PT2 >> 10) & 7;                              \
                                                          \
      TST2_ENTER  TST2_ENTER  TST2_ENTER  TST2_ENTER      \
      TST2_ENTER  TST2_ENTER  TST2_ENTER  TST2_ENTER      \
      TST2_ENTER  TST2_ENTER  TST2_ENTER  TST2_ENTER      \
                                                          \
      TST2_LEAVE  TST2_LEAVE  TST2_LEAVE  TST2_LEAVE      \
      TST2_LEAVE  TST2_LEAVE  TST2_LEAVE  TST2_LEAVE      \
      TST2_LEAVE  TST2_LEAVE  TST2_LEAVE  TST2_LEAVE      \
                                                          \
      C = &WALK[PT1 ^ 5];                                 \
      D = &WALK[PT2 ^ 5];                                 \
                                                          \
      RES[i++] ^= *A;                                     \
      RES[i++] ^= *B;                                     \
      RES[i++] ^= *C;                                     \
      RES[i++] ^= *D;                                     \
                                                          \
      IN = (*A >> ( 9)) ^ (*A << (23)) ^ CLK;             \
      *A = (*B >> (10)) ^ (*B << (22)) ^ CLK;             \
      *B = IN ^ U2;                                       \
      *C = (*C >> (11)) ^ (*C << (21)) ^ CLK;             \
      *D = (*D >> (12)) ^ (*D << (20)) ^ CLK;             \
                                                          \
      A = &WALK[PT1 ^ 6]; RES[i++] ^= *A;                 \
      B = &WALK[PT2 ^ 3]; RES[i++] ^= *B;                 \
      C = &WALK[PT1 ^ 7]; RES[i++] ^= *C;                 \
      D = &WALK[PT2 ^ 7]; RES[i++] ^= *D;                 \
                                                          \
      IN = (*A >> (13)) ^ (*A << (19)) ^ CLK;             \
      *A = (*B >> (14)) ^ (*B << (18)) ^ CLK;             \
      *B = IN;                                            \
      *C = (*C >> (15)) ^ (*C << (17)) ^ CLK;             \
      *D = (*D >> (16)) ^ (*D << (16)) ^ CLK;             \
                                                          \
      PT1 = ( RES[( i - 8 ) ^ PTX] ^                      \
              WALK[PT1 ^ PTX ^ 7] ) & (~1);               \
      PT1 ^= (PT2 ^ 0x10) & 0x10;                         \
                                                          \
      for( n++, i = 0; i < 16; i++ )                      \
          hs->pool[n % MBEDTLS_HAVEGE_COLLECT_SIZE] ^= RES[i];
  
  /*
   * Entropy gathering function
   */
  static void havege_fill( mbedtls_havege_state *hs )
  {
      int i, n = 0;
      int  U1,  U2, *A, *B, *C, *D;
      int PT1, PT2, *WALK, RES[16];
      int PTX, PTY, CLK, PTEST, IN;
  
      WALK = hs->WALK;
      PT1  = hs->PT1;
      PT2  = hs->PT2;
  
      PTX  = U1 = 0;
      PTY  = U2 = 0;
  
      (void)PTX;
  
      memset( RES, 0, sizeof( RES ) );
  
      while( n < MBEDTLS_HAVEGE_COLLECT_SIZE * 4 )
      {
          ONE_ITERATION
          ONE_ITERATION
          ONE_ITERATION
          ONE_ITERATION
      }
  
      hs->PT1 = PT1;
      hs->PT2 = PT2;
  
      hs->offset[0] = 0;
      hs->offset[1] = MBEDTLS_HAVEGE_COLLECT_SIZE / 2;
  }
  
  /*
   * HAVEGE initialization
   */
  void mbedtls_havege_init( mbedtls_havege_state *hs )
  {
      memset( hs, 0, sizeof( mbedtls_havege_state ) );
  
      havege_fill( hs );
  }
  
  void mbedtls_havege_free( mbedtls_havege_state *hs )
  {
      if( hs == NULL )
          return;
  
      mbedtls_platform_zeroize( hs, sizeof( mbedtls_havege_state ) );
  }
  
  /*
   * HAVEGE rand function
   */
  int mbedtls_havege_random( void *p_rng, unsigned char *buf, size_t len )
  {
      int val;
      size_t use_len;
      mbedtls_havege_state *hs = (mbedtls_havege_state *) p_rng;
      unsigned char *p = buf;
  
      while( len > 0 )
      {
          use_len = len;
          if( use_len > sizeof(int) )
              use_len = sizeof(int);
  
          if( hs->offset[1] >= MBEDTLS_HAVEGE_COLLECT_SIZE )
              havege_fill( hs );
  
          val  = hs->pool[hs->offset[0]++];
          val ^= hs->pool[hs->offset[1]++];
  
          memcpy( p, &val, use_len );
  
          len -= use_len;
          p += use_len;
      }
  
      return( 0 );
  }
  
  #endif /* MBEDTLS_HAVEGE_C */
  