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413 lines
12 KiB
413 lines
12 KiB
% Copyright (C) 2018 TANSORIER.
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% Permission is granted to copy, distribute and/or modify this document
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% under the terms of the GNU Free Documentation License, Version 1.3
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% or any later version published by the Free Software Foundation;
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% with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
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% A copy of the license is included in the section entitled "GNU
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% Free Documentation License".
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% https://www.gnu.org/licenses/fdl-1.3.html
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% compress option to have horyzontal circle
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\documentclass[compress,aspectratio=169]{beamer}
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\usepackage{listings}
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% L'option "[fragile]" doit être rajouté au frame pour pouvoir utiliser correctement
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\usepackage{color}
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\lstset{
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breaklines=true,
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tabsize=4,
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}
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% Pour utiliser des colonnes
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\usepackage{multicol}
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% Pour integrer un pdf
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\usepackage[final]{pdfpages}
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% Pour les hyperliens
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\usepackage{hyperref}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\title[U-Boot]{fitImage \& signature de paquets \\ \textbf{Introduction}}
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\author[Mickaël Tansorier]{Mickaël Tansorier}
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\date[Août 2018]{Présentation du fonctionnement des fitImage et \newline du fonctionnement de signature de paquets}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\begin{document}
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%\tableofcontents[subsectionstyle=hide]
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% *******************************
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% **** PAGE DE GARDE ****
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% *******************************
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\begin{frame}
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\titlepage
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\end{frame}
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% *******************************
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% **** INTRODUCTION ****
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% *******************************
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\begin{frame}{Plan}
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\tableofcontents[hideallsubsections]
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\end{frame}
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\section{Introduction}
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\begin{frame}{Images Linux}
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\begin{itemize}
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\item \textbf{Image}: image générique binaire
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\item \textbf{zImage}: image générique binaire compressé
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\item \textbf{uImage}: image avec une entête d'information utilisé par U-Boot
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\item \textbf{fitImage}: enveloppe d'image pouvant contenir plusieurs noyaux, devicetree, firmware. Chaque image peut être signé, et d'autres choses
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\end{itemize}
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\end{frame}
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{
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\setbeamercolor{background canvas}{bg=}
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\includepdf[pages=12-13]{docs/Vasut--secure_and_flexible_boot_with_u-boot_bootloader.pdf}
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}
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{
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\setbeamercolor{background canvas}{bg=}
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\includepdf[pages=22]{docs/Josserand-schulz-secure-boot.pdf}
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}
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% *******************************
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% **** PRÉSENTATION ****
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% *******************************
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\section{Construire fitImage}
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\subsection{Les sources mainline}
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\begin{frame}[fragile]
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% Prevent first column disapear
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\begin{columns}\begin{column}{0.2\textwidth}\end{column}\end{columns}
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\begin{lstlisting}[style=shell,basicstyle=\tiny\ttfamily\color{white}]
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KERNEL=/path/to/zImage
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KEYNAME=my_key
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\end{lstlisting}
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\begin{columns}
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\begin{column}{0.5\textwidth}
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\begin{lstlisting}[style=shell,basicstyle=\tiny\ttfamily\color{white}]
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/dts-v1/;
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/ {
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description = "fitImage for sign Kernel image and DTB";
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#address-cells = <1>;
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images {
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kernel@1 {
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description = "Linux Kenel";
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data = /incbin/("%KERNEL%");
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type = "kernel";
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arch = "arm";
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os = "linux";
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compression = "none";
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load = <0x12000000>;
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entry = <0x12000000>;
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signature@1 {
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algo = "sha256,rsa4096";
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key-name-hint = "%KEYNAME%";
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};
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};
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\end{lstlisting}
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\end{column}
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\begin{column}{0.5\textwidth}
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\begin{lstlisting}[style=shell,basicstyle=\tiny\ttfamily\color{white}]
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fdt@1 {
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description = "Devicetree";
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data = /incbin/("%DTB%");
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type = "flat_dt";
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arch = "arm";
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compression = "none";
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load = <0x18000000>;
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entry = <0x18000000>;
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signature@1 {
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algo = "sha256,rsa4096";
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key-name-hint = "%KEYNAME%";
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};
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};
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};
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configurations {
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default = "conf@1";
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conf@1 {
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kernel = "kernel@1";
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fdt = "fdt@1";
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};
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};
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};
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\end{lstlisting}
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\end{column}
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\end{columns}
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\end{frame}
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\begin{frame}[fragile]
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Plusieurs type de signature sont disponible: \texttt{common/image-sig.c}
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\begin{lstlisting}[style=shell,basicstyle=\tiny\ttfamily\color{white}]
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struct image_sig_algo image_sig_algos[] = {
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{
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"sha1,rsa2048",
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rsa_sign,
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rsa_add_verify_data,
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rsa_verify,
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&checksum_algos[0],
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},
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{
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"sha256,rsa2048",
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rsa_sign,
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rsa_add_verify_data,
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rsa_verify,
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&checksum_algos[1],
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},
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{
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"sha256,rsa4096",
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rsa_sign,
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rsa_add_verify_data,
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rsa_verify,
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&checksum_algos[2],
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}
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};
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\end{lstlisting}
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\end{frame}
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\subsection{Ajouter les clés dans uboot}
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\begin{frame}[fragile]
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Crée un devicetree spécifique
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\begin{lstlisting}
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/dts-v1/;
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/ {
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model = "Keys";
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compatible ="vendor,board";
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signature {
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key-%KEYNAME% {
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required = "image";
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algo = "sha256,rsa4096";
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key-name-hint = "%KEYNAME%";
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};
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};
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};
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\end{lstlisting}
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\end{frame}
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\begin{frame}[fragile]
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Pour le générer le dtb
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\begin{lstlisting}[style=shell]
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dtc -p 4096 $(@D)/u-boot_pubkey.dts -O dtb -o $(@D)/u-boot_pubkey.dtb
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\end{lstlisting}
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Ce qui donne:
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\begin{lstlisting}[style=shell]
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$ cat u-boot_pubkey.dtb
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vendor,board signature key-my_key image sha256,rsa4096 my_key modelcompatiblerequiredalgokey-name-hint
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\end{lstlisting}
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\end{frame}
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\begin{frame}[fragile]
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Pour y ajouter la clé public
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\begin{lstlisting}[style=shell]
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mkimage -D "-I dts -O dtb -p 4096" -f $(@D)/fitImage.its -K $(@D)/u-boot_pubkey.dtb -k $(@D) -r fitImage
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\end{lstlisting}
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Ce qui donne:
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\begin{lstlisting}[style=shell]
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$ cat u-boot_pubkey.dtb
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vendor,board signature key-my_key
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[...]
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image sha256,rsa4096 my_key modelcompatiblerequiredalgokey-name-hintrsa,num-bitrsa,n0-inversersa,exponentrsa,modulusra,r-squaredsquared
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\end{lstlisting}
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\end{frame}
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\begin{frame}[fragile]
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Pour s'assurer que le device tree contenant la clé public soit dans dans le binaire u-boot, il faut que cette option soit à non:
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\begin{lstlisting}[style=shell]
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BR2_TARGET_UBOOT_USE_CUSTOM_CONFIG
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\end{lstlisting}
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Pour ajouter dans notre U-boot alors que l'on a pas de dtb, on utiliser l'option EXT\_DTB de make:
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\begin{lstlisting}[style=shell]
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make CROSS_COMPILE=arm-linux-gnueabihf- EXT_DTB=u-boot_pubkey.dtb
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\end{lstlisting}
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\end{frame}
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\subsection{Signer l'image noyau}
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\begin{frame}[fragile]
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Ok maintenant il faut siqner le kernel linux.\newline
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Il faut le signer avant de compiler u-boot puisque pour ajouter la clé public au devicetree il faut executer mkimge avec en entrée l'its et en sortier le fitImage:
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\begin{lstlisting}[style=shell]
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mkimage -D "-I dts -O dtb -p 4096" -f $(@D)/fitImage.its -K $(@D)/u-boot_pubkey.dtb -k $(@D) -r fitImage
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\end{lstlisting}
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Le noyau Linux est bien construit avant U-boot, donc pas besoin d'ajouter de dépendance.
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\end{frame}
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% *******************************
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% **** PRÉSENTATION ****
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% *******************************
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\section{Paramétrer buildroot - fitImage}
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\subsection{uboot}
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\begin{frame}[fragile]
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J'ai rajouté quelques config dans buildroot.
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\begin{lstlisting}[style=shell]
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BR2_PACKAGE_UBOOT_TOOLS_FIT_SUPPORT=y
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BR2_PACKAGE_UBOOT_TOOLS_FIT_SIGNATURE_SUPPORT=y
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BR2_PACKAGE_HOST_UBOOT_TOOLS=y
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BR2_PACKAGE_HOST_UBOOT_TOOLS_FIT_SUPPORT=y
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BR2_PACKAGE_HOST_UBOOT_TOOLS_FIT_SIGNATURE_SUPPORT=y
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BR2_TARGET_UBOOT_NEEDS_OPENSSL=y
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BR2_TARGET_UBOOT_SIGN_FITIMAGE=y
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BR2_TARGET_UBOOT_ITS="$(CONFIG_DIR)/board/eolane/modx6/fitImage.its"
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BR2_TARGET_UBOOT_SIGN_DTS="$(CONFIG_DIR)/board/eolane/modx6/u-boot_pubkey.dts"
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BR2_TARGET_UBOOT_KEY_NAME="my_key"
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BR2_TARGET_UBOOT_KEY_SERVER="bep@hgweb:/home/apache/distribution/keys/"
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\end{lstlisting}
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\end{frame}
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\begin{frame}[fragile]{Vérification de la signature}
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il est possible de tester la signature d'une image avec:
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\begin{lstlisting}[style=shell]
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fit_check_sign -f output/images/fitImage -k u-boot_pubkey.dtb
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\end{lstlisting}
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dans \texttt{./output/build/host-uboot-tools-2017.07/tools/fit\_check\_sign}
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\end{frame}
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\begin{frame}[fragile]
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Documentation:
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\begin{itemize}
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\item \url{https://elinux.org/images/e/e0/Josserand-schulz-secure-boot.pdf}
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\item \url{https://www.denx.de/wiki/pub/U-Boot/Documentation/multi_image_booting_scenarios.pdf}
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\item \url{https://elinux.org/images/8/8a/Vasut--secure_and_flexible_boot_with_u-boot_bootloader.pdf}
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\end{itemize}
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\end{frame}
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% *******************************
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% **** PRÉSENTATION ****
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% *******************************
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\section{Signature de paquets}
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\subsection{Générer les clés}
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\begin{frame}[fragile]
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Il faut une clé paire de clé:
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\begin{lstlisting}[style=shell]
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$ openssl genrsa -out my_key.key 4096
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$ openssl req -batch -new -x509 -key my_key.key -out my_key.crt
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\end{lstlisting}
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Pour extraire le clé publique du certificat
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\begin{lstlisting}[style=shell]
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openssl x509 -pubkey -noout -in my_key.crt > my_key.pub
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\end{lstlisting}
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\end{frame}
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\subsection{Signer}
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\begin{frame}[fragile]
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Pour signer:
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\begin{lstlisting}[style=shell]
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openssl dgst -sha256 -sign my_key.key -out file_to_sign.sha256 file_to_sign
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\end{lstlisting}
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Si la signature est sous forme binaire, on peut la convertir sous forme textuel:
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\begin{lstlisting}[style=shell]
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openssl base64 -in file_to_sign.sha256 -out file_to_sign.sign
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\end{lstlisting}
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\end{frame}
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\subsection{Vérifier}
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\begin{frame}[fragile]
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Pour signer:
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\begin{lstlisting}[style=shell]
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openssl dgst -sha256 -verify my_key.pub -signature file_to_sign.sha256 file_to_sign
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\end{lstlisting}
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Si la signature est sous forme binaire, on peut la convertir sous forme textuel:
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\begin{lstlisting}[style=shell]
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openssl base64 -d -in file_to_sign.sign -out file_to_sign.sha256
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\end{lstlisting}
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\end{frame}
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% *******************************
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% **** PRÉSENTATION ****
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% *******************************
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\section*{Conclusion}
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\begin{frame}
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\begin{center}
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\begin{huge}
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Question ?
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\end{huge}
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\end{center}
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\begin{center}
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\textcolor{gray}{\tiny{Enfin je vais essayer de répondre...}}
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\end{center}
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\end{frame}
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\end{document}
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