XML signature wrapping attack poses a great threat to the integrity of web services. This is evident in the losses suffered by the Amazon Company in the past. This paper presents a new algorithm called the Spatial Information Approach (SIA). The paper forges the digital signature based on the principle of ratio signature which is adopted from a study in cancer detection. SIA creates a spatial map of the entire SOAP message where its performance is compared to SESoap, another current method that faithfully constructs a digital signature from the whole message. The experiment was conducted in a controlled lab environment by using open source tools in Linux Ubuntu environment. Based on the experiment conducted, SIA is superior to SESoap in terms of performance that shows improvement of the processing speed by approximately 4-14% for messages of size 50 Kb to 750 Kb.