CH12: s/fingerprint/(digest|commitment)/

Makes the test more consistent with other changes made in previous
chapters.

ch10.asciidoc

@@ -903,14 +903,15 @@ until the desired hash result appears by chance.
 ((("Proof-of-Work algorithm", id="proof10")))((("mining and consensus",
 "Proof-of-Work algorithm", id="Cproof10")))A hash algorithm takes an
 arbitrary-length data input and produces a fixed-length deterministic
-result, a digital fingerprint of the input. For any specific input, the
-resulting hash will always be the same and can be easily calculated and
+result, called a _digest_.  The digest is a digital commitment to the
+input. For any specific input, the resulting digest will always be the
+same and can be easily calculated and
 verified by anyone implementing the same hash algorithm.
 ((("collisions")))The key characteristic of a cryptographic hash
 algorithm is that it is computationally infeasible to find two different
-inputs that produce the same fingerprint (known as a _collision_). As a
+inputs that produce the same digest (known as a _collision_). As a
 corollary, it is also virtually impossible to select an input in such a
-way as to produce a desired fingerprint, other than trying random
+way as to produce a desired digest, other than trying random
 inputs.
 
 With SHA256, the output is always 256 bits long, regardless of the size