sxt: max size buffer added;

include/sxt/sxtkey.h

@@ -36,6 +36,8 @@ typedef uint8_t ed25519_pubkey[ED25519_PK_LEN];
 typedef uint8_t ed25519_privkey[ED25519_SK_LEN];
 typedef uint8_t ed25519_signature[ED25519_SIG_LEN];
 
+#define SXT_PPKP_MAXCSIZE  1024*1024
+
 /* flags */
 #define SXT_PPKP_PRIVATE  (1 << 2)
 #define SXT_PPKP_PUBLIC   (1 << 1)