Make SSL_BUFFER_LEN overhead depend more on config
diff --git a/include/polarssl/ssl.h b/include/polarssl/ssl.h
index 91e3981..9db0fc6 100644
--- a/include/polarssl/ssl.h
+++ b/include/polarssl/ssl.h
@@ -249,7 +249,9 @@
* Note: the RFC defines the default size of SSL / TLS messages. If you
* change the value here, other clients / servers may not be able to
* communicate with you anymore. Only change this value if you control
- * both sides of the connection and have it reduced at both sides!
+ * both sides of the connection and have it reduced at both sides, or
+ * if you're using the Max Fragment Length extension and you know all your
+ * peers are using it too!
*/
#if !defined(SSL_MAX_CONTENT_LEN)
#define SSL_MAX_CONTENT_LEN 16384 /**< Size of the input / output buffer */
@@ -258,8 +260,8 @@
/* \} name SECTION: Module settings */
/*
- * Allow an extra 301 bytes for the record header and encryption overhead:
- * counter (8) + header (5) + IV(16) + MAC (48) + padding (256)
+ * Allow extra bytes for record, authentication and encryption overhead:
+ * counter (8) + header (5) + IV(16) + MAC (16-48) + padding (0-256)
* and allow for a maximum of 1024 of compression expansion if
* enabled.
*/
@@ -269,8 +271,36 @@
#define SSL_COMPRESSION_ADD 0
#endif
-#define SSL_BUFFER_LEN (SSL_MAX_CONTENT_LEN + SSL_COMPRESSION_ADD + 333)
+#if defined(POLARSSL_RC4_C) || defined(POLARSSL_CIPHER_MODE_CBC)
+/* Ciphersuites using HMAC */
+#if defined(POLARSSL_SHA512_C)
+#define SSL_MAC_ADD 48 /* SHA-384 used for HMAC */
+#elif defined(POLARSSL_SHA256_C)
+#define SSL_MAC_ADD 32 /* SHA-256 used for HMAC */
+#else
+#define SSL_MAC_ADD 20 /* SHA-1 used for HMAC */
+#endif
+#else
+/* AEAD ciphersuites: GCM and CCM use a 128 bits tag */
+#define SSL_MAC_ADD 16
+#endif
+#if defined(POLARSSL_CIPHER_MODE_CBC)
+#define SSL_PADDING_ADD 256
+#else
+#define SSL_PADDING_ADD 0
+#endif
+
+#define SSL_BUFFER_LEN ( SSL_MAX_CONTENT_LEN \
+ + SSL_COMPRESSION_ADD \
+ + 29 /* counter + header + IV */ \
+ + SSL_MAC_ADD \
+ + SSL_PADDING_ADD \
+ )
+
+/*
+ * Signaling ciphersuite values (SCSV)
+ */
#define SSL_EMPTY_RENEGOTIATION_INFO 0xFF /**< renegotiation info ext */
/*
