CH05::determistic key generation:revise

- Use updated terminology introduced in previous commits.

- Provide a very simple example of deterministic key generation.

- Tease the next section.

ch05.asciidoc

@@ -61,23 +61,56 @@ Modern wallet applications don't independently generate keys but instead
 derive them from a single random seed using a repeatable (deterministic)
 algorithm.
 
-==== Deterministic (Seeded) Wallets
-
-((("wallets", "types of", "deterministic (seeded)
-wallets")))Deterministic, or "seeded," wallets are wallets that contain
-private keys that are all derived from a common seed, through the use of
-a one-way hash function. The seed is a randomly generated number that is
-combined with other data, such as an index number or "chain code" (see
-<<hd_wallets>>) to derive the private keys. In a deterministic wallet,
-the seed is sufficient to recover all the derived keys, and therefore a
-single backup at creation time is sufficient. The seed is also
-sufficient for a wallet export or import, allowing for easy migration of
-all the user's keys between different wallet implementations.
-<<Type1_wallet>> shows a logical diagram of a deterministic wallet.
+==== Deterministic Key Generation
+
+A hash function will always produce the same output when given the same
+input, but if the input is changed even slightly, the output will be
+different.  If the function is cryptographically secure, nobody should
+be able to predict the new output--not even if they know the new input.
+
+This allows us to take one random value and transform it into a
+practically unlimited number of seemingly-random values.  Even more
+usefully, later using the same hash function with the same input
+(called a _seed_) will produce the same seemingly-random values.
+
+----
+# Collect some entropy (randomness)
+$ dd if=/dev/random count=1 status=none | sha256sum
+f1cc3bc03ef51cb43ee7844460fa5049e779e7425a6349c8e89dfbb0fd97bb73  -
+
+# Set our seed to the random value
+$ seed=f1cc3bc03ef51cb43ee7844460fa5049e779e7425a6349c8e89dfbb0fd97bb73
+
+# Deterministically generate derived values
+$ for i in {0..2} ; do echo "$seed + $i" | sha256sum ; done
+50b18e0bd9508310b8f699bad425efdf67d668cb2462b909fdb6b9bd2437beb3  -
+a965dbcd901a9e3d66af11759e64a58d0ed5c6863e901dfda43adcd5f8c744f3  -
+19580c97eb9048599f069472744e51ab2213f687d4720b0efc5bb344d624c3aa  -
+----
+
+If we use the derived values as our private keys, we can later generate
+exactly those same private keys by using our seed value with the
+algorithm we used before.  A user of deterministic key generation can
+back up every key in their wallet by simply recording their seed and
+a reference to the deterministic algorithm they used.  For example, even
+if Alice has a million bitcoins received to a million different
+addresses, all she needs to back up in order to later recover access to
+those bitcoins is:
+
+----
+f1cc 3bc0 3ef5 1cb4 3ee7 8444 60fa 5049
+e779 e742 5a63 49c8 e89d fbb0 fd97 bb73
+----
+
+A logical diagram of basic sequential deterministic key generation is
+shown in <<Type1_wallet>>.  However, modern wallet applications have a
+more clever way of accomplishing this that allows public keys to be
+derived separately from their corresponding private keys, making it
+possible to store private keys more securely than public keys.
 
 [[Type1_wallet]]
 [role="smallersixty"]
-.Type-1 deterministic (seeded) wallet: a deterministic sequence of keys derived from a seed
+.Deterministic key generation: a deterministic sequence of keys derived from a seed for a wallet database
 image::images/mbc2_0502.png["Deterministic Wallet"]
 
 [[hd_wallets]]