This exercise asks you to consider sources of errors in thumbprints (see Section 25.6.2.3). Recall that a thumbprint is computed from the contents of a connection over some interval of time. Consider clocks on two different computers. Initially, they are synchronized. After some period of time has passed, the clocks will show different times. This is called clock skew.
a. Why might clock skew introduce differences in the thumbprints of a connection?
b. Why might propagation delays introduce differences in the thumbprints of a connection?
c. Staniford-Chen and Heberlein computed thumbprints based on contents only, rather than on contents plus information gleaned from the packet header. Suppose they computed the thumbprint over the contents plus the packet header. What errors might this introduce? Could they have chosen some fields of the TCP and IP headers that would not have introduced errors? If so, state which ones, and why.