1 This directory contains a reference implementation for Chrome OS 2 verified boot in firmware. 3 4 ---------- 5 Directory Structure 6 ---------- 7 8 The source is organized into distinct modules - 9 10 firmware/ 11 12 Contains ONLY the code required by the BIOS to validate the secure boot 13 components. There shouldn't be any code in here that signs or generates 14 images. BIOS should require ONLY this directory to implement secure boot. 15 Refer to firmware/README for futher details. 16 17 cgpt/ 18 19 Utility to read/write/modify GPT partitions. Similar to GNU parted or any 20 other GPT tool, but this has support for Chrome OS extensions. 21 22 host/ 23 24 Miscellaneous functions needed by userland utilities. 25 26 futility/ 27 28 The "firmware utility" tool, used to create, sign, and validate Chrome OS 29 images. 30 31 utility/ 32 33 Random other utilities, not necesssarily related to verified boot as such. 34 35 tests/ 36 37 User-land tests and benchmarks that test the reference implementation. 38 Please have a look at these if you'd like to understand how to use the 39 reference implementation. 40 41 build/ 42 43 The output directory where the generated files will be placed, and where 44 tests are run. 45 46 scripts/ 47 48 Tools and scripts used to generate and use new signing keypairs. These are 49 typically used only on a secure machine. 50 51 52 -------------------- 53 Building and testing 54 -------------------- 55 56 The suite can be built on the host or in the chroot environment. 57 58 Building on the host could fail if certain packages are not installed. If 59 there are host environment build problems due to missing .h files, try 60 researching what packages the files belong to and install the missing packages 61 before reporting a problem. 62 63 64 The commands are the more-or-less expected ones: 65 66 make 67 make runtests 68 make install [ DESTDIR=/usr/local ] 69 70 71 72 ---------- 73 Some useful utilities: 74 ---------- 75 76 futility vbutil_key Convert a public key into .vbpubk format 77 futility vbutil_keyblock Wrap a public key inside a signature and checksum 78 futility vbutil_firmware Create a .vblock with signature info for a 79 firmware image 80 futility vbutil_kernel Pack a kernel image, bootloader, and config into 81 a signed binary 82 83 dumpRSAPublicKey Dump RSA Public key (from a DER-encoded X509 84 certificate) in a format suitable for use by 85 RSAVerify* functions in crypto/. 86 87 verify_data.c Verify a given signature on a given file. 88 89 90 91 ---------- 92 Generating a signed firmware image: 93 ---------- 94 95 * Step 0: Build the tools, install them somewhere. 96 97 * Step 1: Generate RSA root and signing keys. 98 99 The root key is always 8192 bits. 100 101 $ openssl genrsa -F4 -out root_key.pem 8192 102 103 The signing key can be between 1024-8192 bits. 104 105 $ openssl genrsa -F4 -out signing_key.pem <1024|2048|4096|8192> 106 107 Note: The -F4 option must be specified to generate RSA keys with a public 108 exponent of 65535. RSA keys with 3 as a public exponent (the default) 109 won't work. 110 111 * Step 2: Generate pre-processed public versions of the above keys using 112 dumpRSAPublicKey. This utility expects an x509 certificate as 113 input, and emits an intermediate representation for further 114 processing. 115 116 $ openssl req -batch -new -x509 -key root_key.pem -out root_key.crt 117 $ openssl req -batch -new -x509 -key signing_key.pem -out signing_key.crt 118 $ dumpRSAPublicKey root_key.crt > root_key.keyb 119 $ dumpRSAPublicKey signing_key.crt > signing_key.keyb 120 121 ************** TODO: STUFF PAST HERE IS OUT OF DATE *************** 122 123 At this point we have all the requisite keys needed to generate a signed 124 firmware image. 125 126 .pem RSA Public/Private Key Pair 127 .crt X509 Key Certificate 128 .keyb Pre-processed RSA Public Key 129 130 131 * Step 3: Use utility/firmware_utility to generate a signed firmare blob. 132 133 $ utility/firmware_utility --generate \ 134 --root_key root_key.pem \ 135 --firmware_sign_key signing_key.pem \ 136 --firmware_sign_key_pub signing_key.keyb \ 137 --firmware_sign_algorithm <algoid> \ 138 --firmware_key_version 1 \ 139 --firmware_version 1 \ 140 --in <firmware blob file> \ 141 --out <output file> 142 143 Where <algoid> is based on the signature algorithm to use for firmware 144 signining. The list of <algoid> specifications can be output by running 145 'utility/firmware_utility' without any arguments. 146 147 Note: --firmware_key_version and --firmware_version are part of a signed 148 image and are used to prevent rollbacks to older version. For testing, 149 they can just be set to valid values. 150 151 152 * Step 4: Verify that this image verifies. 153 154 $ utility/firmware_utility --verify \ 155 --in <signed firmware image> 156 --root_key_pub root_key.keyb 157 Verification SUCCESS. 158 159 160 Note: The verification functions expects a pointer to the 161 pre-processed public root key as input. For testing purposes, 162 root_key.keyb can be stored in RW part of the firmware. For the 163 final firmware, this will be a fixed public key which cannot be 164 changed and must be stored in RO firmware. 165 166 ---------- 167 Generating a signed kernel image: 168 ---------- 169 170 The steps for generating a signed kernel image are similar to that of 171 a firmware image. Since verification is chained - RO firmware verifies 172 RW firmware which verifies the kernel, only the keys change. An additional 173 kernel signing key must be generated. The firmware signing generated above 174 is the root key equivalent for signed kernel images. 175
