Add functions for read/write ECPoint records

include/polarssl/ecp.h

@@ -33,6 +33,7 @@
  * ECP error codes
  */
 #define POLARSSL_ERR_ECP_BAD_INPUT_DATA                    -0x4F80  /**< Bad input parameters to function. */
+#define POLARSSL_ERR_ECP_BUFFER_TOO_SMALL                  -0x4F80  /**< The buffer is too small to write to. */
 #define POLARSSL_ERR_ECP_GENERIC                           -0x4F00  /**<  Generic ECP error */
 
 /**
@@ -117,15 +118,15 @@ ecp_group;
 #define POLARSSL_ECP_WINDOW_SIZE    7   /**< Maximum NAF width used. */
 
 /*
- * Point formats
+ * Point formats, from RFC 4492's enum ECPointFormat
  */
 #define POLARSSL_ECP_PF_UNCOMPRESSED    0   /**< Uncompressed point format */
 #define POLARSSL_ECP_PF_COMPRESSED      1   /**< Compressed point format */
 
 /*
- * Some constants from RFC 4492 (ECC for TLS)
+ * Some other constants from RFC 4492
  */
-#define POLARSSL_ECP_TLS_NAMED_CURVE    3   /**< ECCurveType named_curve */
+#define POLARSSL_ECP_TLS_NAMED_CURVE    3   /**< ECCurveType's named_curve */
 
 
 #ifdef __cplusplus
@@ -239,14 +240,16 @@ int ecp_group_read_string( ecp_group *grp, int radix,
  * \param grp       Group to which the point should belong
  * \param P         Point to export
  * \param format    Point format, should be a POLARSSL_ECP_PF_XXX macro
- * \param olen      Length of the actual ouput
+ * \param olen      Length of the actual output
  * \param buf       Output buffer
  * \param buflen    Length of the output buffer
  *
- * \return          0 if successful, or POLARSSL_ERR_ECP_GENERIC
+ * \return          0 if successful,
+ *                  or POLARSSL_ERR_ECP_BAD_INPUT_DATA
+ *                  or POLARSSL_ERR_ECP_BUFFER_TOO_SMALL
  */
 int ecp_write_binary( const ecp_group *grp, const ecp_point *P, int format,
-                      size_t *olen, unsigned char *buf, size_t buflen );
+                      uint8_t *olen, unsigned char *buf, size_t buflen );
 
 /**
  * \brief           Import a point from unsigned binary data
@@ -284,7 +287,7 @@ int ecp_read_binary( const ecp_group *grp, ecp_point *P, int format,
 int ecp_use_known_dp( ecp_group *grp, uint16_t index );
 
 /**
- * \brief           Read a group from an ECParameters record
+ * \brief           Set a group from a TLS ECParameters record
  *
  * \param grp       Destination group
  * \param buf       Start of input buffer
@@ -296,6 +299,37 @@ int ecp_use_known_dp( ecp_group *grp, uint16_t index );
  */
 int ecp_tls_read_group( ecp_group *grp, const unsigned char *buf, size_t len );
 
+/**
+ * \brief           Import a point from a TLS ECPoint record
+ *
+ * \param grp       ECP group used
+ * \param pt        Destination point
+ * \param buf       Start of input buffer
+ * \param len       Buffer length
+ *
+ * \return          O if successful,
+ *                  POLARSSL_ERR_MPI_XXX if initialization failed
+ *                  POLARSSL_ERR_ECP_BAD_INPUT_DATA if input is invalid
+ */
+int ecp_tls_read_point( const ecp_group *grp, ecp_point *pt,
+                        const unsigned char *buf, size_t len );
+
+/**
+ * \brief           Export a point as a TLS ECPoint record
+ *
+ * \param grp       ECP group used
+ * \param pt        Point to export
+ * \param format    Export format
+ * \param buf       Buffer to write to
+ * \param len       Buffer length
+ *
+ * \return          0 if successful,
+ *                  or POLARSSL_ERR_ECP_BAD_INPUT_DATA
+ *                  or POLARSSL_ERR_ECP_BUFFER_TOO_SMALL
+ */
+int ecp_tls_write_point( const ecp_group *grp, const ecp_point *pt,
+                         int format, unsigned char *buf, size_t buf_len );
+
 /**
  * \brief           Addition: R = P + Q
  *

library/ecp.c

@@ -186,14 +186,14 @@ cleanup:
  * Export a point into unsigned binary data (SEC1 2.3.3)
  */
 int ecp_write_binary( const ecp_group *grp, const ecp_point *P, int format,
-                      size_t *olen, unsigned char *buf, size_t buflen )
+                      uint8_t *olen, unsigned char *buf, size_t buflen )
 {
     int ret;
     size_t plen;
 
     if( format != POLARSSL_ECP_PF_UNCOMPRESSED &&
         format != POLARSSL_ECP_PF_COMPRESSED )
-        return( POLARSSL_ERR_ECP_GENERIC );
+        return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
 
     /*
      * Common case: P == 0
@@ -201,7 +201,7 @@ int ecp_write_binary( const ecp_group *grp, const ecp_point *P, int format,
     if( mpi_cmp_int( &P->Z, 0 ) == 0 )
     {
         if( buflen < 1 )
-            return( POLARSSL_ERR_ECP_GENERIC );
+            return( POLARSSL_ERR_ECP_BUFFER_TOO_SMALL );
 
         buf[0] = 0x00;
         *olen = 1;
@@ -216,7 +216,7 @@ int ecp_write_binary( const ecp_group *grp, const ecp_point *P, int format,
         *olen = 2 * plen + 1;
 
         if( buflen < *olen )
-            return( POLARSSL_ERR_ECP_GENERIC );
+            return( POLARSSL_ERR_ECP_BUFFER_TOO_SMALL );
 
         buf[0] = 0x04;
         MPI_CHK( mpi_write_binary( &P->X, buf + 1, plen ) );
@@ -227,7 +227,7 @@ int ecp_write_binary( const ecp_group *grp, const ecp_point *P, int format,
         *olen = plen + 1;
 
         if( buflen < *olen )
-            return( POLARSSL_ERR_ECP_GENERIC );
+            return( POLARSSL_ERR_ECP_BUFFER_TOO_SMALL );
 
         buf[0] = 0x02 + mpi_get_bit( &P->Y, 0 );
         MPI_CHK( mpi_write_binary( &P->X, buf + 1, plen ) );
@@ -264,6 +264,49 @@ cleanup:
     return( ret );
 }
 
+/*
+ * Import a point from a TLS ECPoint record (RFC 4492)
+ *      struct {
+ *          opaque point <1..2^8-1>;
+ *      } ECPoint;
+ */
+int ecp_tls_read_point( const ecp_group *grp, ecp_point *pt,
+                        const unsigned char *buf, size_t buf_len )
+{
+    unsigned char data_len;
+
+    /*
+     * We must have at least two bytes (1 for length, at least of for data)
+     */
+    if( buf_len < 2 )
+        return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
+
+    data_len = *buf++;
+    if( data_len < 1 || data_len > buf_len - 1 )
+        return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
+
+    return ecp_read_binary( grp, pt, POLARSSL_ECP_PF_UNCOMPRESSED,
+            buf, data_len );
+}
+
+/*
+ * Export a point as a TLS ECPoint record (RFC 4492)
+ *      struct {
+ *          opaque point <1..2^8-1>;
+ *      } ECPoint;
+ */
+int ecp_tls_write_point( const ecp_group *grp, const ecp_point *pt,
+                         int format, unsigned char *buf, size_t buf_len )
+{
+    /*
+     * buf_len must be at least one, for our length byte
+     */
+    if( buf_len < 1 )
+        return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
+
+    return ecp_write_binary( grp, pt, format, buf, buf + 1, buf_len - 1);
+}
+
 /*
  * Wrapper around fast quasi-modp functions, with fall-back to mpi_mod_mpi.
  * See the documentation of struct ecp_group.