crypto + spelling

Author: llpeterson

crypto.rst

@@ -9,17 +9,18 @@ cryptography. So we begin our study of technical approaches to network
 security with an overview of cryptography.
 
 We introduce the concepts of cryptography-based security step by step.
-The first step is the cryptographic algorithms—ciphers and cryptographic
-hashes—that are introduced in this chapter. Such algorithms are not a solution in
-themselves, but provide building blocks from which a solution can be
-built. Cryptographic algorithms are parameterized by *keys*. The
-distribution of keys is in itself a challenge which we tackle in a later
-chapter.
+The first step is the cryptographic algorithms—ciphers and
+cryptographic hashes—that are introduced in this chapter. Such
+algorithms are not a solution in themselves, but provide building
+blocks from which a solution can be built. For example, cryptographic
+algorithms are parameterized by *keys*, with the distribution of keys
+a challenge that we tackle in the next chapter.
 
 Once we have a set of cryptographic algorithms and a way to distribute
 keys, we are in a position to build protocols that enable secure
-communication between participants. The final chapter describes several
-complete security protocols and systems in current use.
+communication between participants. Later chapters describes several
+such security protocols, culminating in a description of complete
+systems that use these protocols.
 
 3.1 Principles of Ciphers
 ---------------------------
@@ -80,12 +81,12 @@ there are plenty of people who will try to break ciphers and who will
 let it be widely known when they have succeeded.
 
 Parameterizing a cipher with keys provides us with what is in effect a
-very large family of ciphers; by switching keys, we are
-switching to another cipher in the family. It is common to limit the amount
-of data that a *cryptanalyst* (code-breaker) can access before the key
-changes. This provides the attacker with less ability to break the cipher
-(for reasons discussed below) and limits the damage done if the code is
-broken.
+very large family of ciphers; by switching keys, we are switching to
+another cipher in the family. It is common to limit the amount of data
+that a *cryptanalyst* (code-breaker) can access before the key
+changes. This provides the attacker with less ability to break the
+cipher, for reasons discussed below. It also limits the damage done if
+the code is broken.
 
 The basic requirement for an encryption algorithm is that it turns
 plaintext into ciphertext in such a way that only the intended
@@ -102,10 +103,10 @@ plaintext was written in English, which means that the letter *e*
 occurs more often in the plaintext that any other letter; the
 frequency of many other letters and common letter combinations can
 also be predicted. With simple ciphers, this information could greatly
-simplify the task of finding the key. Similarly, the attacker may know
-something about the likely contents of the message; for example, the
+simplify the task of determining the key. Similarly, the attacker may know
+something about the likely contents of the message. For example, the
 word “login” is likely to occur at the start of a remote login
-session. Common headers appear at the start of HTTP messages. This may
+session, and common headers appear at the start of HTTP messages. This may
 enable a *known plaintext* attack, which has a much higher chance of
 success than a *ciphertext only* attack. Even better is a *chosen
 plaintext* attack, which may be enabled by feeding some information to
@@ -207,18 +208,11 @@ overly large blocks. For this reason most ciphers today have settled
 on 128-bit blocks. Some details on how the birthday attacks were shown
 to be an issue is available at the "Sweet32" website.
 
-
-
 .. admonition:: Further Reading
 
    Sweet32. `Birthday attacks on 64-bit block ciphers in TLS and OpenVPN
    <https://sweet32.info>`__.
 
-
-
-
-
-
 3.2 Secret-Key Ciphers
 ------------------------
 
@@ -233,10 +227,15 @@ at the alternative, public-key ciphers, shortly. (Public-key ciphers
 are known as also asymmetric-key ciphers, since as we’ll soon see, the
 two participants use different keys.)
 
-.. [#] We use the term *participant* for the parties involved in a
-       secure communication since that is a common networking term to
-       identify the two endpoints of a communication channel. In the
-       security world, the parties are often called *principals*.
+.. [#] We use *participants* as a generic term for the endpoints of a
+       communication channel. Depending on the layer of the network
+       stack, a participant might correspond to a server, a process, a
+       mailbox, or some other system abstraction. In the context of
+       security, the communicating parties are often called
+       *principals*, which in turn implies *identify*, and ultimately,
+       an association with a human that can be held accountable. We
+       use the term principal in place of participant when this full
+       meaning is central to the discussion.
 
 The U.S. National Institute of Standards and Technology (NIST) has
 issued standards for a series of secret-key ciphers. *Data Encryption
@@ -478,7 +477,7 @@ knows a secret that is known only to the alleged sender
 of the message; for example, the secret could be a key, and the proof
 could be some value encrypted using the key. There is a mutual
 dependency between the way the code is generated and how it is used as
-proof of secret knowledge. We will discuss several workable
+proof of secret knowledge. The following discusses several workable
 combinations.
 
 For simplicity, let's assume initially that the original message need
@@ -487,7 +486,7 @@ plaintext of the original message plus some additional code to support
 authentication. Later we will consider the case where confidentiality
 is also desired.
 
-One common build block of message authentication is a
+One common building block of message authentication is a
 *cryptographic hash function*. Cryptographic hash algorithms are
 treated as public knowledge, as with cipher algorithms. A
 cryptographic hash function is a function that outputs sufficient
@@ -579,8 +578,7 @@ public-key ciphers, one based on RSA, another based on elliptic
 curves, and a third called the *Edwards-Curve Digital Signature
 Algorithm*.
 
-
-An widely used alternative approach to encrypting a hash is to use a
+A widely used alternative approach to encrypting a hash is to use a
 hash function that takes a secret value (a key known only to the
 sender and the receiver) as an input parameter in addition to the
 message text. Such a function outputs a message authentication code
@@ -592,7 +590,7 @@ compares that recomputed code to the code received in the message. The
 most common approaches to generating these codes are called HMACs or
 keyed-hash message authentication codes.
 
-HMACs can use any hash function of the sort described above, but the
+HMACs can use any hash function of the sort described above, but
 also include the key as part of the material to be hashed, so that a
 HMAC is a function of both the key and the input text. An approach to
 calculating HMACs has been standardized by NIST and takes the
@@ -657,9 +655,6 @@ and hash functions, among other cryptographic concepts, we recommend the followi
    A. Menezes, P. van Oorschot, and S. Vanstone. `Handbook of Applied
    Cryptography <https://cacr.uwaterloo.ca/hac/>`__. CRC Press, 1996.
 
-
-
-
 Now that we have seen some of the building blocks for encryption and
 authentication, we have the foundations for building some complete security
 solutions. Before we get to those, however, we address the issue of how participants