Added ecp_write_binary().

include/polarssl/ecp.h

@@ -209,6 +209,20 @@ int ecp_group_read_string( ecp_group *grp, int radix,
                            const char *p, const char *b,
                            const char *gx, const char *gy, const char *n);
 
+/**
+ * \brief           Export a point into unsigned binary data, uncompressed
+ *
+ * \param grp       Group the point belongs to
+ * \param P         Point to export
+ * \param olen      Length of the actual ouput
+ * \param buf       Output buffer
+ * \param buflen    Length of the output buffer
+ *
+ * \return          0 if successful, or POLARSSL_ERR_ECP_GENERIC
+ */
+int ecp_write_binary( const ecp_group *grp, const ecp_point *P,
+                      size_t *olen, unsigned char *buf, size_t buflen );
+
 /**
  * \brief           Set a group using well-known domain parameters
  *

library/ecp.c

@@ -173,6 +173,43 @@ cleanup:
     return( ret );
 }
 
+/*
+ * Export a point into unsigned binary data, uncompressed format (SEC1 2.3.3)
+ */
+int ecp_write_binary( const ecp_group *grp, const ecp_point *P,
+                      size_t *olen, unsigned char *buf, size_t buflen )
+{
+    int ret;
+    size_t plen;
+
+    /*
+     * Case P == 0
+     */
+    if( mpi_cmp_int( &P->Z, 0 ) == 0 )
+    {
+        if( buflen < 1 )
+            return( POLARSSL_ERR_ECP_GENERIC );
+
+        buf[0] = 0x00;
+        *olen = 1;
+
+        return( 0 );
+    }
+
+    plen = mpi_size( &grp->P );
+    *olen = 2 * plen + 1;
+
+    if( buflen < *olen )
+        return( POLARSSL_ERR_ECP_GENERIC );
+
+    buf[0] = 0x04;
+    MPI_CHK( mpi_write_binary( &P->X, buf + 1, plen ) );
+    MPI_CHK( mpi_write_binary( &P->Y, buf + 1 + plen, plen ) );
+
+cleanup:
+    return( ret );
+}
+
 /*
  * Wrapper around fast quasi-modp functions, with fall-back to mpi_mod_mpi.
  * See the documentation of struct ecp_group.

tests/suites/test_suite_ecp.data

@@ -133,6 +133,18 @@ ecp_small_check_pub:0:2:1:0
 ECP small check pubkey #10
 ecp_small_check_pub:10:25:1:POLARSSL_ERR_ECP_GENERIC
 
+ECP write binary #1 (zero, buffer just fits)
+ecp_write_binary:SECP192R1:"01":"01":"00":"00":1:0
+
+ECP write binary #2 (zero, buffer too small)
+ecp_write_binary:SECP192R1:"01":"01":"00":"00":0:POLARSSL_ERR_ECP_GENERIC
+
+ECP write binary #3 (non-zero, buffer just fits)
+ecp_write_binary:SECP192R1:"48d8082a3a1e3112bc03a8ef2f6d40d0a77a6f8e00cc9933":"6ceed4d7cba482e288669ee1b6415626d6f34d28501e060c":"01":"0448d8082a3a1e3112bc03a8ef2f6d40d0a77a6f8e00cc99336ceed4d7cba482e288669ee1b6415626d6f34d28501e060c":49:0
+
+ECP write binary #4 (non-zero, buffer too small)
+ecp_write_binary:SECP192R1:"48d8082a3a1e3112bc03a8ef2f6d40d0a77a6f8e00cc9933":"6ceed4d7cba482e288669ee1b6415626d6f34d28501e060c":"01":"0448d8082a3a1e3112bc03a8ef2f6d40d0a77a6f8e00cc99336ceed4d7cba482e288669ee1b6415626d6f34d28501e060c":48:POLARSSL_ERR_ECP_GENERIC
+
 ECP mod p192 readable
 ecp_fast_mod:SECP192R1:"000000000000010500000000000001040000000000000103000000000000010200000000000001010000000000000100"
 

tests/suites/test_suite_ecp.function

@@ -224,6 +224,39 @@ ecp_fast_mod:id:N
 }
 END_CASE
 
+BEGIN_CASE
+ecp_write_binary:id:x:y:z:out:blen:ret
+{
+    ecp_group grp;
+    ecp_point P;
+    unsigned char buf[256], str[512];
+    size_t olen;
+
+    memset( buf, 0, sizeof( buf ) );
+    memset( str, 0, sizeof( str ) );
+
+    ecp_group_init( &grp ); ecp_point_init( &P );
+
+    TEST_ASSERT( ecp_use_known_dp( &grp, POLARSSL_ECP_DP_{id} ) == 0 );
+
+    TEST_ASSERT( mpi_read_string( &P.X, 16, {x} ) == 0 );
+    TEST_ASSERT( mpi_read_string( &P.Y, 16, {y} ) == 0 );
+    TEST_ASSERT( mpi_read_string( &P.Z, 16, {z} ) == 0 );
+
+    TEST_ASSERT( ecp_write_binary( &grp, &P, &olen, buf, {blen} ) == {ret} );
+
+    if( {ret} == 0 )
+    {
+        TEST_ASSERT( olen == strlen({out}) / 2 );
+
+        hexify( str, buf, {blen} );
+        TEST_ASSERT( strcasecmp( (char *) str, {out} ) == 0 );
+    }
+
+    ecp_group_free( &grp ); ecp_point_free( &P );
+}
+END_CASE
+
 BEGIN_CASE
 ecp_selftest:
 {