Increase hamming distance for some error codes
The MBEDTLS_ERR_SSL_WANT_READ and MBEDTLS_ERR_SSL_WANT_WRITE are
errors that can be ignored, so increase the hamming distance between
them and the non-ignorable errors and keep still some distance from
a success case. This mitigates an attack where single bit-flipping could
change a non-ignorable error to being an ignorable one.
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 4609e73..b99be93 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -125,8 +125,8 @@
#define MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED -0x6A80 /**< DTLS client must retry for hello verification */
#define MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL -0x6A00 /**< A buffer is too small to receive or write a message */
#define MBEDTLS_ERR_SSL_NO_USABLE_CIPHERSUITE -0x6980 /**< None of the common ciphersuites is usable (eg, no suitable certificate, see debug messages). */
-#define MBEDTLS_ERR_SSL_WANT_READ -0x6900 /**< No data of requested type currently available on underlying transport. */
-#define MBEDTLS_ERR_SSL_WANT_WRITE -0x6880 /**< Connection requires a write call. */
+#define MBEDTLS_ERR_SSL_WANT_READ -0xFF6900 /**< No data of requested type currently available on underlying transport. */
+#define MBEDTLS_ERR_SSL_WANT_WRITE -0xFF6880 /**< Connection requires a write call. */
#define MBEDTLS_ERR_SSL_TIMEOUT -0x6800 /**< The operation timed out. */
#define MBEDTLS_ERR_SSL_CLIENT_RECONNECT -0x6780 /**< The client initiated a reconnect from the same port. */
#define MBEDTLS_ERR_SSL_UNEXPECTED_RECORD -0x6700 /**< Record header looks valid but is not expected. */