Add timestamp/serial to cookies, with timeout
diff --git a/library/ssl_cookie.c b/library/ssl_cookie.c
index 0fce65a..fa0aabc 100644
--- a/library/ssl_cookie.c
+++ b/library/ssl_cookie.c
@@ -55,24 +55,35 @@
* with max 32 bytes of cookie for DTLS 1.0
*/
#if defined(POLARSSL_SHA256_C)
-#define COOKIE_MD POLARSSL_MD_SHA224
-#define COOKIE_MD_LEN 32
-#define COOKIE_MD_USE 28
+#define COOKIE_MD POLARSSL_MD_SHA224
+#define COOKIE_MD_OUTLEN 32
+#define COOKIE_HMAC_LEN 28
#elif defined(POLARSSL_SHA512_C)
-#define COOKIE_MD POLARSSL_MD_SHA384
-#define COOKIE_MD_LEN 48
-#define COOKIE_MD_USE 28
+#define COOKIE_MD POLARSSL_MD_SHA384
+#define COOKIE_MD_OUTLEN 48
+#define COOKIE_HMAC_LEN 28
#elif defined(POLARSSL_SHA1_C)
-#define COOKIE_MD POLARSSL_MD_SHA1
-#define COOKIE_MD_LEN 20
-#define COOKIE_MD_USE 20
+#define COOKIE_MD POLARSSL_MD_SHA1
+#define COOKIE_MD_OUTLEN 20
+#define COOKIE_HMAC_LEN 20
#else
#error "DTLS hello verify needs SHA-1 or SHA-2"
#endif
+/*
+ * Cookies are formed of a 4-bytes timestamp (or serial number) and
+ * an HMAC of timestemp and client ID.
+ */
+#define COOKIE_LEN ( 4 + COOKIE_HMAC_LEN )
+
+#define COOKIE_TIMEOUT 60
+
void ssl_cookie_init( ssl_cookie_ctx *ctx )
{
md_init( &ctx->hmac_ctx );
+#if !defined(POLARSSL_HAVE_TIME)
+ ctx->serial = 0;
+#endif
}
void ssl_cookie_free( ssl_cookie_ctx *ctx )
@@ -85,7 +96,7 @@
void *p_rng )
{
int ret;
- unsigned char key[COOKIE_MD_LEN];
+ unsigned char key[COOKIE_MD_OUTLEN];
if( ( ret = f_rng( p_rng, key, sizeof( key ) ) ) != 0 )
return( ret );
@@ -104,33 +115,63 @@
}
/*
+ * Generate the HMAC part of a cookie
+ */
+static int ssl_cookie_hmac( md_context_t *hmac_ctx,
+ const unsigned char time[4],
+ unsigned char **p, unsigned char *end,
+ const unsigned char *cli_id, size_t cli_id_len )
+{
+ int ret;
+ unsigned char hmac_out[COOKIE_MD_OUTLEN];
+
+ if( (size_t)( end - *p ) < COOKIE_HMAC_LEN )
+ return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
+
+ if( ( ret = md_hmac_reset( hmac_ctx ) ) != 0 ||
+ ( ret = md_hmac_update( hmac_ctx, time, 4 ) ) != 0 ||
+ ( ret = md_hmac_update( hmac_ctx, cli_id, cli_id_len ) ) != 0 ||
+ ( ret = md_hmac_finish( hmac_ctx, hmac_out ) ) != 0 )
+ {
+ return( POLARSSL_ERR_SSL_INTERNAL_ERROR );
+ }
+
+ memcpy( *p, hmac_out, COOKIE_HMAC_LEN );
+ *p += COOKIE_HMAC_LEN;
+
+ return( 0 );
+}
+
+/*
* Generate cookie for DTLS ClientHello verification
*/
int ssl_cookie_write( void *p_ctx,
unsigned char **p, unsigned char *end,
const unsigned char *cli_id, size_t cli_id_len )
{
- int ret;
- unsigned char hmac_out[COOKIE_MD_LEN];
ssl_cookie_ctx *ctx = (ssl_cookie_ctx *) p_ctx;
+ unsigned long t;
if( ctx == NULL || cli_id == NULL )
return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
- if( (size_t)( end - *p ) < COOKIE_MD_USE )
+ if( (size_t)( end - *p ) < COOKIE_LEN )
return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
- if( ( ret = md_hmac_reset( &ctx->hmac_ctx ) ) != 0 ||
- ( ret = md_hmac_update( &ctx->hmac_ctx, cli_id, cli_id_len ) ) != 0 ||
- ( ret = md_hmac_finish( &ctx->hmac_ctx, hmac_out ) ) != 0 )
- {
- return( POLARSSL_ERR_SSL_INTERNAL_ERROR );
- }
+#if defined(POLARSSL_HAVE_TIME)
+ t = (unsigned long) time( NULL );
+#else
+ t = ctx->serial++;
+#endif
- memcpy( *p, hmac_out, COOKIE_MD_USE );
- *p += COOKIE_MD_USE;
+ (*p)[0] = (unsigned char)( t >> 24 );
+ (*p)[1] = (unsigned char)( t >> 16 );
+ (*p)[2] = (unsigned char)( t >> 8 );
+ (*p)[3] = (unsigned char)( t );
+ *p += 4;
- return( 0 );
+ return( ssl_cookie_hmac( &ctx->hmac_ctx, *p - 4,
+ p, end, cli_id, cli_id_len ) );
}
/*
@@ -140,18 +181,37 @@
const unsigned char *cookie, size_t cookie_len,
const unsigned char *cli_id, size_t cli_id_len )
{
- unsigned char ref_cookie[COOKIE_MD_USE];
- unsigned char *p = ref_cookie;
+ unsigned char ref_hmac[COOKIE_HMAC_LEN];
+ unsigned char *p = ref_hmac;
+ ssl_cookie_ctx *ctx = (ssl_cookie_ctx *) p_ctx;
+ unsigned long cur_time, cookie_time;
- if( cookie_len != COOKIE_MD_USE )
+ if( ctx == NULL || cli_id == NULL )
+ return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
+
+ if( cookie_len != COOKIE_LEN )
return( -1 );
- if( ssl_cookie_write( p_ctx,
- &p, p + sizeof( ref_cookie ),
- cli_id, cli_id_len ) != 0 )
+ if( ssl_cookie_hmac( &ctx->hmac_ctx, cookie,
+ &p, p + sizeof( ref_hmac ),
+ cli_id, cli_id_len ) != 0 )
return( -1 );
- if( safer_memcmp( cookie, ref_cookie, sizeof( ref_cookie ) ) != 0 )
+ if( safer_memcmp( cookie + 4, ref_hmac, sizeof( ref_hmac ) ) != 0 )
+ return( -1 );
+
+#if defined(POLARSSL_HAVE_TIME)
+ cur_time = (unsigned long) time( NULL );
+#else
+ cur_time = ctx->serial;
+#endif
+
+ cookie_time = ( (unsigned long) cookie[0] << 24 ) |
+ ( (unsigned long) cookie[1] << 16 ) |
+ ( (unsigned long) cookie[2] << 8 ) |
+ ( (unsigned long) cookie[3] );
+
+ if( cur_time - cookie_time > COOKIE_TIMEOUT )
return( -1 );
return( 0 );