Populate TLS <= 1.2 handshake source files

This commit moves generic/client/server handshake handling
code from ssl_tls.c, ssl_cli.c and ssl_srv.c to the newly
created files ssl_12_gen.c, ssl_12_cli.c and ssl_12_srv.c.

No functional changes have been made. Changes are confined to
moving, reordering, and commenting the code for ease of reading.

include/mbedtls/ssl_internal.h

@@ -1101,4 +1101,8 @@ void mbedtls_ssl_buffering_free( mbedtls_ssl_context *ssl );
 void mbedtls_ssl_flight_free( mbedtls_ssl_flight_item *flight );
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
 
+#if defined(MBEDTLS_X509_CRT_PARSE_C)
+void mbedtls_ssl_clear_peer_cert( mbedtls_ssl_session *session );
+#endif /* MBEDTLS_X509_CRT_PARSE_C */
+
 #endif /* ssl_internal.h */

library/ssl_msg.c

@@ -458,6 +458,51 @@ static void ssl_extract_add_data_from_record( unsigned char* add_data,
     }
 }
 
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+/*
+ * SSLv3.0 MAC functions
+ */
+#define SSL_MAC_MAX_BYTES   20  /* MD-5 or SHA-1 */
+static void ssl_mac( mbedtls_md_context_t *md_ctx,
+                     const unsigned char *secret,
+                     const unsigned char *buf, size_t len,
+                     const unsigned char *ctr, int type,
+                     unsigned char out[SSL_MAC_MAX_BYTES] )
+{
+    unsigned char header[11];
+    unsigned char padding[48];
+    int padlen;
+    int md_size = mbedtls_md_get_size( md_ctx->md_info );
+    int md_type = mbedtls_md_get_type( md_ctx->md_info );
+
+    /* Only MD5 and SHA-1 supported */
+    if( md_type == MBEDTLS_MD_MD5 )
+        padlen = 48;
+    else
+        padlen = 40;
+
+    memcpy( header, ctr, 8 );
+    header[ 8] = (unsigned char)  type;
+    header[ 9] = (unsigned char)( len >> 8 );
+    header[10] = (unsigned char)( len      );
+
+    memset( padding, 0x36, padlen );
+    mbedtls_md_starts( md_ctx );
+    mbedtls_md_update( md_ctx, secret,  md_size );
+    mbedtls_md_update( md_ctx, padding, padlen  );
+    mbedtls_md_update( md_ctx, header,  11      );
+    mbedtls_md_update( md_ctx, buf,     len     );
+    mbedtls_md_finish( md_ctx, out              );
+
+    memset( padding, 0x5C, padlen );
+    mbedtls_md_starts( md_ctx );
+    mbedtls_md_update( md_ctx, secret,    md_size );
+    mbedtls_md_update( md_ctx, padding,   padlen  );
+    mbedtls_md_update( md_ctx, out,       md_size );
+    mbedtls_md_finish( md_ctx, out                );
+}
+#endif /* MBEDTLS_SSL_PROTO_SSL3 */
+
 int mbedtls_ssl_encrypt_buf( mbedtls_ssl_context *ssl,
                              mbedtls_ssl_transform *transform,
                              mbedtls_record *rec,