Add fourth easy piece to intro

easy.typ

@@ -11,8 +11,8 @@
 }
 
 #show: evan.with(
-  title: "Three Easy Pieces in Programmable Cryptography",
-  long-title: [Three Easy Pieces in \ Programmable \ Cryptography],
+  title: "Four Easy Pieces in Programmable Cryptography",
+  long-title: [Four Easy Pieces in \ Programmable \ Cryptography],
   author: "0xPARC",
   date: datetime.today(),
 )

src/bigbook-frontmatter.typ

@@ -3,7 +3,7 @@
 = About this novel
 
 This novel _Notes on Programmable Cryptography_ is a sequel
-to the novella _Three Easy Pieces in Programmable Cryptography_,
+to the novella Four Easy Pieces in Programmable Cryptography_,
 from the #link("https://0xparc.org", "0xPARC Foundation").
 Whereas the novella was short enough to print and give to friends
 as a souvenir to read on a plane ride,

src/intro.typ

@@ -86,7 +86,7 @@ statements of the form:
 once the statement is encoded as a system of equations. One such statement would be "I know $M$ such that $sha(M) = Y$."
 
 SNARKS are an active area of research, and many different SNARKs are known.
-Our work focuses on a particular example, PLONK (@plonk).
+We will focus on a particular example, PLONK (@plonk).
 
 == FHE: Fully homomorphic encryption
 
@@ -106,6 +106,30 @@ another language and give you $Enc(y)$, where $y$ is the translation of $x$.
 You can then decrypt and obtain $y$, knowing that the server cannot extract
 anything meaningful from $Enc(x)$ without your secret key.
 
+== ORAM: Oblivious RAM
+
+You want to perform a private computation on a large database.
+The database is so large that you can't store it yourself --
+and you don't trust the server it's stored on.
+
+First off, you'll encrypt the data, so the server can't read it.
+But the server still has an attack:
+they can study your #emph[access patterns].
+For example, they can see which records you access most frequently,
+or which records you access at the same time as other records.
+In many applications this is enough for the server to learn
+sensitive information.
+
+Oblivious RAM protects against exactly this sort of attack.
+Oblivious RAM is an algorithm you use to "scramble" your
+memory access requests.
+When you feed your request into the ORAM algorithm,
+the ORAM algorithm sends some scrambled
+read and write requests to the server.
+Only one of the scrambled requests is the request you are interested in;
+the others keep the server from learning
+which request you care about.
+
 = Programmable Cryptography in the World
 
 In the past decade, there has been a surprisingly high amount of theoretical work but also