A client application, when executed by a processor, is operative to create a HyperText Transfer Protocol (HTTP) request containing a target header that includes a confidential value. The HTTP request is to be sent over a Secure Sockets Layer (SSL) 3.0 connection or a Transport Layer Security (TLS) 1.0 connection to a web server. The client application implements at its HTTP layer a countermeasure to a blockwise chosen-boundary attack. The client application generates an additional header having a header name that is not recognizable by the web server and inserts the additional header into the HTTP request ahead of the target header, thus creating a modified HTTP request. The modified HTTP request is to be sent, instead of the unmodified HTTP request, over the SSL 3.0 connection or the TLS 1.0 connection to the web server.