Add report for BadParity

.gitignore

@@ -22,3 +22,6 @@ genesis.json
 
 # Ignore enodes
 enodes
+
+# Ignore minted stuff
+_minted-report2

project2/report2.tex

@@ -9,6 +9,10 @@
 \usepackage[english]{babel}
 \usepackage{fancyhdr}
 \usepackage{titling}
+\usepackage{minted} 
+\usepackage{xcolor} % to access the named colour LightGray
+\definecolor{LightGray}{gray}{0.9}
+
 \renewcommand{\thesection}{Exercise \Alph{section}:}
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@@ -63,7 +67,68 @@ Our group consists of the following members:
 \end{center}
 
 \section{Bad Parity}
-% Fill here your answers for exercise A 
+
+For this challenge we were given two contracts: \texttt{Wallet} and
+\texttt{WalletLibrary}. The second contract is used by the \texttt{Wallet}
+contract to set the owner upon initialization, to get the current owner, to
+change the owner and to withdraw funds from the wallet. These functions are
+called from the \texttt{Wallet} contract through the use of the
+\texttt{delegatecall} function. In contrast to a regular \texttt{call},
+\texttt{delegatecall} executes the function in the context of the \emph{calling}
+smart contract. This means that if there happens to be a variable in both
+contracts with the same name and a function changes that variable, the
+\emph{caller's} and not the \emph{callee's} variable is changed. If insufficient
+care is exercised during programming, the semantics of \texttt{delegatecall} can
+have serious security implications, as in this case with \texttt{Wallet} and
+\texttt{WalletLibrary}.
+
+The \texttt{fallback} function in \texttt{Wallet} is called when the smart
+contract receives a transaction with empty call data or call data which does not
+match any other function. The call data sent with the transaction is then passed
+to the \texttt{WalletLibrary} contract via \texttt{delegatecall}. The
+\texttt{WalletLibrary} contract has a function called \texttt{initWallet} which
+sets the owner of the contract to the given address. Usually this function would
+be called only upon initialization of the contract (in the constructor for
+example). We can call this function at any time by supplying the correct call
+data to the \texttt{fallback} function from the \texttt{Wallet} contract. Since
+the function is then called via \texttt{delegatecall}, the owner of the
+\texttt{Wallet} contract is changed to an address of our choosing.
+
+To trigger the \texttt{initWallet} function, the call data must contain the
+signature of the function and all parameters. The function signature is the
+first four bytes of the keccak hash of the function name and the types of its
+parameters. Any parameters are added to the signature in a padded form. Creating
+the call data in python works as follows (where \texttt{address} is the address
+of the new owner):
+\begin{minted}[frame=lines,framesep=2mm,bgcolor=LightGray,fontsize=\footnotesize,linenos]{python}
+sig = w3.keccak(text='initWallet(address)')[:4].hex() + address[2:].rjust(64, '0')
+# sig = 0x9da8be21000000000000000000000000f9ac06BAeb6597511C22Dc7b03DA447cA893fb4e
+\end{minted}
+
+We can then send this call data to the contract (via the geth console):
+\begin{minted}[frame=lines,framesep=2mm,bgcolor=LightGray,fontsize=\footnotesize,linenos]{python}
+eth.sendTransaction({
+  from: student,
+  to: badparityAddress,
+  data: "0x9da8be21000000000000000000000000f9ac06BAeb6597511C22Dc7b03DA447cA893fb4e", 
+  gas: "80000"
+});
+\end{minted}
+The owner of the \texttt{Wallet} contract is now our own address. Since we are
+the owner, we can call the \texttt{withdraw} function from the \texttt{Wallet}
+contract:
+\begin{minted}[frame=lines,framesep=2mm,bgcolor=LightGray,fontsize=\footnotesize,linenos,breaklines]{python}
+sig = w3.keccak(text='withdraw(uint256)')[:4].hex() + hex(30000000000000000000)[2:].rjust(64, '0')
+# sig = 0x2e1a7d4d000000000000000000000000000000000000000000000001a055690d9db80000
+eth.sendTransaction({
+  from: student,
+  to: badparityAddress,
+  data: "0x2e1a7d4d000000000000000000000000000000000000000000000001a055690d9db80000", 
+  gas: "80000"
+});
+\end{minted}
+
+Our own balance has increased by 30 Ether.
 
 \section{DAO Down}
 % Fill here your answers for exercise B