From 287781a965bfc1603c6314632803d303ddbf406a Mon Sep 17 00:00:00 2001
From: Paul Bakker <p.j.bakker@polarssl.org>
Date: Sat, 26 Mar 2011 13:18:49 +0000
Subject: [PATCH]  -  Added mpi_fill_random() for centralized filling of big
 numbers with random data (Fixed ticket #10)

---
 ChangeLog                 |  2 ++
 include/polarssl/bignum.h | 13 +++++++++++++
 library/bignum.c          | 31 ++++++++++++++++++-------------
 library/dhm.c             | 12 ++----------
 4 files changed, 35 insertions(+), 23 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index e81cb2ce5..2ea47e304 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -6,6 +6,8 @@ Features
      for the RSAES-OAEP and RSASSA-PSS operations.
    * Reading of Public Key files incorporated into default x509
      functionality as well.
+   * Added mpi_fill_random() for centralized filling of big numbers
+     with random data (Fixed ticket #10)
 
 Changes
    * Debug print of MPI now removes leading zero octets and 
diff --git a/include/polarssl/bignum.h b/include/polarssl/bignum.h
index 79bc354c0..ebc1f8f2f 100644
--- a/include/polarssl/bignum.h
+++ b/include/polarssl/bignum.h
@@ -466,6 +466,19 @@ int mpi_mod_int( t_int *r, const mpi *A, int b );
  */
 int mpi_exp_mod( mpi *X, const mpi *A, const mpi *E, const mpi *N, mpi *_RR );
 
+/**
+ * \brief          Fill an MPI X with size bytes of random
+ *
+ * \param X        Destination MPI
+ * \param size     Size in bytes
+ * \param f_rng    RNG function
+ * \param p_rng    RNG parameter
+ *
+ * \return         0 if successful,
+ *                 1 if memory allocation failed
+ */
+int mpi_fill_random( mpi *X, int size, int (*f_rng)(void *), void *p_rng );
+
 /**
  * \brief          Greatest common divisor: G = gcd(A, B)
  *
diff --git a/library/bignum.c b/library/bignum.c
index 55188b785..8ae3921db 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1559,6 +1559,22 @@ cleanup:
     return( ret );
 }
 
+int mpi_fill_random( mpi *X, int size, int (*f_rng)(void *), void *p_rng )
+{
+    int ret, k;
+    unsigned char *p;
+
+    MPI_CHK( mpi_grow( X, size ) );
+    MPI_CHK( mpi_lset( X, 0 ) );
+
+    p = (unsigned char *) X->p;
+    for( k = 0; k < X->n * ciL; k++ )
+        *p++ = (unsigned char) f_rng( p_rng );
+
+cleanup:
+    return( ret );
+}
+
 #if defined(POLARSSL_GENPRIME)
 
 /*
@@ -1686,7 +1702,6 @@ int mpi_is_prime( mpi *X, int (*f_rng)(void *), void *p_rng )
 {
     int ret, i, j, n, s, xs;
     mpi W, R, T, A, RR;
-    unsigned char *p;
 
     if( mpi_cmp_int( X, 0 ) == 0 ||
         mpi_cmp_int( X, 1 ) == 0 )
@@ -1740,11 +1755,7 @@ int mpi_is_prime( mpi *X, int (*f_rng)(void *), void *p_rng )
         /*
          * pick a random A, 1 < A < |X| - 1
          */
-        MPI_CHK( mpi_grow( &A, X->n ) );
-
-        p = (unsigned char *) A.p;
-        for( j = 0; j < A.n * ciL; j++ )
-            *p++ = (unsigned char) f_rng( p_rng );
+        mpi_fill_random( &A, X->n, f_rng, p_rng );
 
         if( mpi_cmp_mpi( &A, &W ) >= 0 )
         {
@@ -1804,7 +1815,6 @@ int mpi_gen_prime( mpi *X, int nbits, int dh_flag,
                    int (*f_rng)(void *), void *p_rng )
 {
     int ret, k, n;
-    unsigned char *p;
     mpi Y;
 
     if( nbits < 3 )
@@ -1814,12 +1824,7 @@ int mpi_gen_prime( mpi *X, int nbits, int dh_flag,
 
     n = BITS_TO_LIMBS( nbits );
 
-    MPI_CHK( mpi_grow( X, n ) );
-    MPI_CHK( mpi_lset( X, 0 ) );
-
-    p = (unsigned char *) X->p;
-    for( k = 0; k < X->n * ciL; k++ )
-        *p++ = (unsigned char) f_rng( p_rng );
+    mpi_fill_random( X, n, f_rng, p_rng );
 
     k = mpi_msb( X );
     if( k < nbits ) MPI_CHK( mpi_shift_l( X, nbits - k ) );
diff --git a/library/dhm.c b/library/dhm.c
index 9b99a2b17..bcad7fcb3 100644
--- a/library/dhm.c
+++ b/library/dhm.c
@@ -138,12 +138,8 @@ int dhm_make_params( dhm_context *ctx, int x_size,
      * Generate X as large as possible ( < P )
      */
     n = x_size / sizeof( t_int ) + 1;
-    MPI_CHK( mpi_grow( &ctx->X, n ) );
-    MPI_CHK( mpi_lset( &ctx->X, 0 ) );
 
-    p = (unsigned char *) ctx->X.p;
-    for( i = 0; i < x_size; i++ )
-        *p++ = (unsigned char) f_rng( p_rng );
+    mpi_fill_random( &ctx->X, n, f_rng, p_rng );
 
     while( mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
            mpi_shift_r( &ctx->X, 1 );
@@ -220,12 +216,8 @@ int dhm_make_public( dhm_context *ctx, int x_size,
      * generate X and calculate GX = G^X mod P
      */
     n = x_size / sizeof( t_int ) + 1;
-    MPI_CHK( mpi_grow( &ctx->X, n ) );
-    MPI_CHK( mpi_lset( &ctx->X, 0 ) );
 
-    p = (unsigned char *) ctx->X.p;
-    for( i = 0; i < x_size; i++ )
-        *p++ = (unsigned char) f_rng( p_rng );
+    mpi_fill_random( &ctx->X, n, f_rng, p_rng );
 
     while( mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
            mpi_shift_r( &ctx->X, 1 );