Implement hashing function for ZKP

library/ecjpake.c

@@ -21,6 +21,7 @@
 
 /*
  * EC-JPAKE is defined in Chapter 7.4 of the Thread specification.
+ * References below are base on the draft-1.0.0 spec.
  */
 
 #if !defined(MBEDTLS_CONFIG_FILE)
@@ -33,6 +34,90 @@
 
 #include "mbedtls/ecjpake.h"
 
+#include <string.h>
+
+/*
+ * Write a point plus its length to a buffer
+ */
+static int ecjpake_write_len_point( unsigned char **p,
+                                    const unsigned char *end,
+                                    const mbedtls_ecp_group *grp,
+                                    const mbedtls_ecp_point *P )
+{
+    int ret;
+    size_t len;
+
+    /* Need at least 4 for length plus 1 for point */
+    if( end < *p || end - *p < 5 )
+        return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
+
+    ret = mbedtls_ecp_point_write_binary( grp, P, MBEDTLS_ECP_PF_UNCOMPRESSED,
+                                          &len, *p + 4, end - ( *p + 4 ) );
+    if( ret != 0 )
+        return( ret );
+
+    (*p)[0] = (unsigned char)( ( len >> 24 ) & 0xFF );
+    (*p)[1] = (unsigned char)( ( len >> 16 ) & 0xFF );
+    (*p)[2] = (unsigned char)( ( len >>  8 ) & 0xFF );
+    (*p)[3] = (unsigned char)( ( len       ) & 0xFF );
+
+    *p += 4 + len;
+
+    return( 0 );
+}
+
+/*
+ * Size of the temporary buffer for ecjpake_hash:
+ * 3 EC points plus their length, plus ID (6 bytes)
+ */
+#define ECJPAKE_HASH_BUF_LEN    ( 3 * ( 4 + MBEDTLS_ECP_MAX_PT_LEN ) + 6 )
+
+/*
+ * Compute hash for ZKP (7.4.2.2.2.1)
+ */
+static int ecjpake_hash( const mbedtls_md_info_t *md_info,
+                         const mbedtls_ecp_group *grp,
+                         const mbedtls_ecp_point *G,
+                         const mbedtls_ecp_point *V,
+                         const mbedtls_ecp_point *X,
+                         const char *id,
+                         mbedtls_mpi *h )
+{
+    int ret;
+    unsigned char buf[ECJPAKE_HASH_BUF_LEN];
+    unsigned char *p = buf;
+    const unsigned char *end = buf + sizeof( buf );
+    size_t id_len = strlen( id );
+    unsigned char hash[MBEDTLS_MD_MAX_SIZE];
+
+    /* Write things to temporary buffer */
+    MBEDTLS_MPI_CHK( ecjpake_write_len_point( &p, end, grp, G ) );
+    MBEDTLS_MPI_CHK( ecjpake_write_len_point( &p, end, grp, V ) );
+    MBEDTLS_MPI_CHK( ecjpake_write_len_point( &p, end, grp, X ) );
+
+    if( end < p || (size_t)( end - p ) < id_len )
+        return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
+
+    *p++ = (unsigned char)( ( id_len >> 24 ) & 0xFF );
+    *p++ = (unsigned char)( ( id_len >> 16 ) & 0xFF );
+    *p++ = (unsigned char)( ( id_len >>  8 ) & 0xFF );
+    *p++ = (unsigned char)( ( id_len       ) & 0xFF );
+
+    memcpy( p, id, id_len );
+    p += id_len;
+
+    /* Compute hash */
+    mbedtls_md( md_info, buf, p - buf, hash );
+
+    /* Turn it into an integer mod n */
+    MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( h, hash,
+                                        mbedtls_md_get_size( md_info ) ) );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( h, h, &grp->N ) );
+
+cleanup:
+    return( ret );
+}
+
 #if defined(MBEDTLS_SELF_TEST)
 
 #if defined(MBEDTLS_PLATFORM_C)
@@ -42,14 +127,106 @@
 #define mbedtls_printf     printf
 #endif
 
+#if !defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED) || \
+    !defined(MBEDTLS_SHA256_C)
+int mbedtls_ecjpake_self_test( int verbose )
+{
+    (void) verbose;
+    return( 0 );
+}
+#else
+
+static const unsigned char ecjpake_test_G[] = {
+    0x04, 0x6b, 0x17, 0xd1, 0xf2, 0xe1, 0x2c, 0x42, 0x47, 0xf8, 0xbc, 0xe6,
+    0xe5, 0x63, 0xa4, 0x40, 0xf2, 0x77, 0x03, 0x7d, 0x81, 0x2d, 0xeb, 0x33,
+    0xa0, 0xf4, 0xa1, 0x39, 0x45, 0xd8, 0x98, 0xc2, 0x96, 0x4f, 0xe3, 0x42,
+    0xe2, 0xfe, 0x1a, 0x7f, 0x9b, 0x8e, 0xe7, 0xeb, 0x4a, 0x7c, 0x0f, 0x9e,
+    0x16, 0x2b, 0xce, 0x33, 0x57, 0x6b, 0x31, 0x5e, 0xce, 0xcb, 0xb6, 0x40,
+    0x68, 0x37, 0xbf, 0x51, 0xf5
+};
+
+static const unsigned char ecjpake_test_V[] = {
+    0x04, 0xfa, 0x9a, 0x24, 0x9d, 0x73, 0x6e, 0x30, 0x28, 0xd1, 0x2d, 0xf1,
+    0xdc, 0xfa, 0x22, 0xd1, 0xed, 0x62, 0x82, 0xbf, 0xab, 0x27, 0x7c, 0x7c,
+    0x52, 0x56, 0xf3, 0xfd, 0x38, 0x07, 0xa5, 0xae, 0xe0, 0x72, 0xfb, 0x4d,
+    0x9c, 0x2b, 0xd6, 0xa4, 0x70, 0xf7, 0xb4, 0xd0, 0xbd, 0xfb, 0x4a, 0x94,
+    0x96, 0xcf, 0xcd, 0xd3, 0x53, 0xf9, 0x90, 0x3c, 0x0a, 0x69, 0xa4, 0x4b,
+    0x18, 0xc6, 0xd2, 0x9b, 0xb8
+};
+
+static const unsigned char ecjpake_test_X[] = {
+    0x04, 0x52, 0xa4, 0xda, 0x90, 0xa5, 0x15, 0x7f, 0xc0, 0xe5, 0x1f, 0x79,
+    0x4b, 0xe3, 0xbb, 0x3f, 0x1d, 0xf8, 0xdf, 0xb1, 0xe3, 0x18, 0xa8, 0x10,
+    0xf2, 0x05, 0x2e, 0x64, 0xa8, 0xe8, 0x35, 0x64, 0xe8, 0xe2, 0x8c, 0x17,
+    0x15, 0xab, 0xf7, 0x8d, 0x1f, 0x8b, 0x18, 0x99, 0x6d, 0x6a, 0xb7, 0xbd,
+    0xcc, 0xbe, 0x52, 0x08, 0x1a, 0x3a, 0xe7, 0x65, 0x4b, 0xdf, 0x66, 0x62,
+    0xf5, 0x74, 0xe0, 0xfd, 0x80
+};
+
+static const unsigned char ecjpake_test_h[] = {
+    0xec, 0xf3, 0x24, 0x46, 0x16, 0xce, 0xa5, 0x34, 0x58, 0x46, 0xd2, 0x45,
+    0xba, 0x27, 0x63, 0x36, 0x50, 0xc4, 0x70, 0x3d, 0x56, 0x0c, 0x7a, 0x7c,
+    0x51, 0x69, 0xfe, 0xa7, 0xa3, 0xf7, 0x79, 0x10
+};
+
 /*
  * Checkup routine
  */
 int mbedtls_ecjpake_self_test( int verbose )
 {
     int ret;
+    mbedtls_ecp_group grp;
+    mbedtls_ecp_point G, V, X;
+    mbedtls_mpi h, h_ref;
+    const mbedtls_md_info_t *md_info;
 
-    ret = 0; /* XXX */
+    mbedtls_ecp_group_init( &grp );
+    mbedtls_ecp_point_init( &G );
+    mbedtls_ecp_point_init( &V );
+    mbedtls_ecp_point_init( &X );
+    mbedtls_mpi_init( &h_ref );
+    mbedtls_mpi_init( &h );
+
+    if( verbose != 0 )
+        mbedtls_printf( "  ECJPAKE test #1 (hash): " );
+
+    md_info = mbedtls_md_info_from_type( MBEDTLS_MD_SHA256 );
+    MBEDTLS_MPI_CHK( mbedtls_ecp_group_load( &grp, MBEDTLS_ECP_DP_SECP256R1 ) );
+    MBEDTLS_MPI_CHK( mbedtls_ecp_point_read_binary( &grp, &G, ecjpake_test_G,
+                                                      sizeof( ecjpake_test_G ) ) );
+    MBEDTLS_MPI_CHK( mbedtls_ecp_point_read_binary( &grp, &V, ecjpake_test_V,
+                                                      sizeof( ecjpake_test_V ) ) );
+    MBEDTLS_MPI_CHK( mbedtls_ecp_point_read_binary( &grp, &X, ecjpake_test_X,
+                                                      sizeof( ecjpake_test_X ) ) );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &h_ref, ecjpake_test_h,
+                                              sizeof( ecjpake_test_h ) ) );
+
+    MBEDTLS_MPI_CHK( ecjpake_hash( md_info, &grp, &G, &V, &X, "client", &h ) );
+
+    if( mbedtls_mpi_cmp_mpi( &h, &h_ref ) != 0 )
+    {
+        ret = 1;
+        goto cleanup;
+    }
+
+    if( verbose != 0 )
+        mbedtls_printf( "passed\n" );
+
+cleanup:
+    mbedtls_ecp_group_free( &grp );
+    mbedtls_ecp_point_free( &G );
+    mbedtls_ecp_point_free( &V );
+    mbedtls_ecp_point_free( &X );
+    mbedtls_mpi_free( &h_ref );
+    mbedtls_mpi_free( &h );
+
+    if( ret != 0 )
+    {
+        if( verbose != 0 )
+            mbedtls_printf( "failed\n" );
+
+        ret = 1;
+    }
 
     if( verbose != 0 )
         mbedtls_printf( "\n" );
@@ -57,6 +234,8 @@ int mbedtls_ecjpake_self_test( int verbose )
     return( ret );
 }
 
+#endif /* MBEDTLS_ECP_DP_SECP256R1_ENABLED && MBEDTLS_SHA256_C */
+
 #endif /* MBEDTLS_SELF_TEST */
 
 #endif /* MBEDTLS_ECJPAKE_C */