Support for seed file writing and reading in Entropy

ChangeLog

@@ -1,6 +1,9 @@
 PolarSSL ChangeLog
 
 = Branch 1.2
+Features
+   * Entropy module now supports seed writing and reading
+
 Changes
    * Introduced POLARSSL_HAVE_READDIR_R for systems without it
    * Improvements to the CMake build system, contributed by Julian Ospald.

include/polarssl/entropy.h

@@ -39,6 +39,7 @@
 #define POLARSSL_ERR_ENTROPY_SOURCE_FAILED                 -0x003C  /**< Critical entropy source failure. */
 #define POLARSSL_ERR_ENTROPY_MAX_SOURCES                   -0x003E  /**< No more sources can be added. */
 #define POLARSSL_ERR_ENTROPY_NO_SOURCES_DEFINED            -0x0040  /**< No sources have been added to poll. */
+#define POLARSSL_ERR_ENTROPY_FILE_IO_ERROR                 -0x0058  /**< Read/write error in file. */
 
 #if !defined(POLARSSL_CONFIG_OPTIONS)
 #define ENTROPY_MAX_SOURCES     20      /**< Maximum number of sources supported */
@@ -47,6 +48,7 @@
 
 #define ENTROPY_BLOCK_SIZE      64      /**< Block size of entropy accumulator (SHA-512) */
 
+#define ENTROPY_MAX_SEED_SIZE   1024    /**< Maximum size of seed we read from seed file */
 #define ENTROPY_SOURCE_MANUAL   ENTROPY_MAX_SOURCES
 
 #ifdef __cplusplus
@@ -146,6 +148,34 @@ int entropy_func( void *data, unsigned char *output, size_t len );
 int entropy_update_manual( entropy_context *ctx,
                            const unsigned char *data, size_t len );
 
+#if defined(POLARSSL_FS_IO)
+/**
+ * \brief               Write a seed file
+ *
+ * \param ctx           Entropy context
+ * \param path          Name of the file
+ *
+ * \return              0 if successful,
+ *                      POLARSSL_ERR_ENTROPY_FILE_IO_ERROR on file error, or
+ *                      POLARSSL_ERR_ENTROPY_SOURCE_FAILED
+ */
+int entropy_write_seed_file( entropy_context *ctx, const char *path );
+
+/**
+ * \brief               Read and update a seed file. Seed is added to this
+ *                      instance. No more than ENTROPY_MAX_SEED_SIZE bytes are
+ *                      read from the seed file. The rest is ignored.
+ *
+ * \param ctx           Entropy context
+ * \param path          Name of the file
+ *
+ * \return              0 if successful,
+ *                      POLARSSL_ERR_ENTROPY_FILE_IO_ERROR on file error,
+ *                      POLARSSL_ERR_ENTROPY_SOURCE_FAILED
+ */
+int entropy_update_seed_file( entropy_context *ctx, const char *path );
+#endif
+
 #ifdef __cplusplus
 }
 #endif

include/polarssl/error.h

@@ -62,6 +62,7 @@
  * CTR_DBRG  3  0x0034-0x003A
  * ENTROPY   3  0x003C-0x0040
  * NET      11  0x0042-0x0056
+ * ENTROPY   1  0x0058-0x0058
  * ASN1      7  0x0060-0x006C
  * MD2       1  0x0070-0x0070
  * MD4       1  0x0072-0x0072

library/entropy.c

@@ -30,6 +30,10 @@
 #include "polarssl/entropy.h"
 #include "polarssl/entropy_poll.h"
 
+#if defined(POLARSSL_FS_IO)
+#include <stdio.h>
+#endif
+
 #if defined(POLARSSL_HAVEGE_C)
 #include "polarssl/havege.h"
 #endif
@@ -201,4 +205,60 @@ int entropy_func( void *data, unsigned char *output, size_t len )
     return( 0 );
 }
 
+#if defined(POLARSSL_FS_IO)
+int entropy_write_seed_file( entropy_context *ctx, const char *path )
+{
+    int ret = POLARSSL_ERR_ENTROPY_FILE_IO_ERROR;
+    FILE *f;
+    unsigned char buf[ENTROPY_BLOCK_SIZE];
+
+    if( ( f = fopen( path, "wb" ) ) == NULL )
+        return( POLARSSL_ERR_ENTROPY_FILE_IO_ERROR );
+
+    if( ( ret = entropy_func( ctx, buf, ENTROPY_BLOCK_SIZE ) ) != 0 )
+        goto exit;
+
+    if( fwrite( buf, 1, ENTROPY_BLOCK_SIZE, f ) != ENTROPY_BLOCK_SIZE )
+    {
+        ret = POLARSSL_ERR_ENTROPY_FILE_IO_ERROR;
+        goto exit;
+    }
+
+    ret = 0;
+
+exit:
+    fclose( f );
+    return( ret );
+}
+
+int entropy_update_seed_file( entropy_context *ctx, const char *path )
+{
+    FILE *f;
+    size_t n;
+    unsigned char buf[ ENTROPY_MAX_SEED_SIZE ];
+
+    if( ( f = fopen( path, "rb" ) ) == NULL )
+        return( POLARSSL_ERR_ENTROPY_FILE_IO_ERROR );
+
+    fseek( f, 0, SEEK_END );
+    n = (size_t) ftell( f );
+    fseek( f, 0, SEEK_SET );
+
+    if( n > ENTROPY_MAX_SEED_SIZE )
+        n = ENTROPY_MAX_SEED_SIZE;
+
+    if( fread( buf, 1, n, f ) != n )
+    {
+        fclose( f );
+        return( POLARSSL_ERR_ENTROPY_FILE_IO_ERROR );
+    }
+
+    fclose( f );
+
+    entropy_update_manual( ctx, buf, n );
+
+    return( entropy_write_seed_file( ctx, path ) );
+}
+#endif /* POLARSSL_FS_IO */
+
 #endif

library/error.c

@@ -508,6 +508,8 @@ void error_strerror( int ret, char *buf, size_t buflen )
         snprintf( buf, buflen, "ENTROPY - No more sources can be added" );
     if( use_ret == -(POLARSSL_ERR_ENTROPY_NO_SOURCES_DEFINED) )
         snprintf( buf, buflen, "ENTROPY - No sources have been added to poll" );
+    if( use_ret == -(POLARSSL_ERR_ENTROPY_FILE_IO_ERROR) )
+        snprintf( buf, buflen, "ENTROPY - Read/write error in file" );
 #endif /* POLARSSL_ENTROPY_C */
 
 #if defined(POLARSSL_GCM_C)