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will-v-piwill-v-pi
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Use key share for AES file
Update CMake tooling to use 128 byte key files (a 4-way share of the 32 byte key). Also temporarily update the enc_bootloader to deshare this key - the actual fix will need to be in aes.S.
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5 files changed

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‎bootloaders/encrypted/README.md

+7-2
Original file line numberDiff line numberDiff line change
@@ -4,10 +4,15 @@ Replace private.pem and privateaes.bin with your own keys - your signing key mus
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openssl ecparam -name secp256k1 -genkey -out private.pem
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```
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7-
The AES key is just be a 32 byte binary file - you can create one with
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The AES key is stored as a 4-way share in a 128 byte binary file - you can create one with
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```bash
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dd if=/dev/urandom of=privateaes.bin bs=1 count=32
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dd if=/dev/urandom of=privateaes.bin bs=1 count=128
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```
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or in Powershell 7
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```powershell
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[byte[]] $(Get-SecureRandom -Maximum 256 -Count 128) | Set-Content privateaes.bin -AsByteStream
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```
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Then either drag & drop the UF2 files to the device in order (enc_bootloader first, then hello_serial_enc) waiting for a reboot in-between, or run

‎bootloaders/encrypted/enc_bootloader.c

+13-1
Original file line numberDiff line numberDiff line change
@@ -180,7 +180,19 @@ int main() {
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init_lut_map();
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// Read key directly from OTP - guarded reads will throw a bus fault if there are any errors
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uint16_t* otp_data = (uint16_t*)OTP_DATA_GUARDED_BASE;
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init_key(rkey_s, (uint8_t*)&(otp_data[(OTP_CMD_ROW_BITS & 0x780)]));
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// Temporary de-sharing - REMOVE THIS AND MODIFY ASM INSTEAD
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uint8_t* shared_key_a = (uint8_t*)&(otp_data[(OTP_CMD_ROW_BITS & 0x780)]);
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uint8_t* shared_key_b = (uint8_t*)&(otp_data[(OTP_CMD_ROW_BITS & 0x790)]);
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uint8_t* shared_key_c = (uint8_t*)&(otp_data[(OTP_CMD_ROW_BITS & 0x7A0)]);
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uint8_t* shared_key_d = (uint8_t*)&(otp_data[(OTP_CMD_ROW_BITS & 0x7B0)]);
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uint8_t deshared_key[32];
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for (int i=0; i < sizeof(deshared_key); i++) {
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deshared_key[i] = shared_key_a[i] ^ shared_key_b[i] ^ shared_key_c[i] ^ shared_key_d[i];
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}
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init_key(rkey_s, deshared_key);
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// init_key(rkey_s, (uint8_t*)&(otp_data[(OTP_CMD_ROW_BITS & 0x780)]));
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otp_hw->sw_lock[30] = 0xf;
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flush_reg();
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ctr_crypt_s(iv, (void*)SRAM_BASE, data_size/16);

‎bootloaders/encrypted/otp.json

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Original file line numberDiff line numberDiff line change
@@ -35,12 +35,108 @@
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"0xc0",
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"0xd0",
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"0xe0",
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"0xf0"
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"0xf0",
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"0x0f",
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"0x0e",
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"0x0d",
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"0x0c",
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"0x0b",
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"0x0a",
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"0x09",
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"0x08",
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"0x07",
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"0x06",
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"0x05",
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"0x04",
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"0x03",
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"0x02",
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"0x01",
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"0x00",
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"0xf0",
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"0xe0",
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"0xd0",
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"0xc0",
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"0xb0",
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"0xa0",
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"0x90",
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"0x80",
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"0x70",
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"0x60",
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"0x50",
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"0x40",
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"0x30",
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"0x20",
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"0x10",
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"0x00",
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"0x08",
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"0x09",
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"0x0a",
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"0x0b",
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"0x0c",
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"0x0d",
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"0x0e",
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"0x0f",
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"0x00",
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"0x01",
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"0x02",
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"0x03",
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"0x04",
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"0x05",
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"0x06",
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"0x07",
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"0x80",
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"0x90",
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"0xa0",
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"0xb0",
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"0xc0",
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"0xd0",
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"0xe0",
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"0xf0",
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"0x00",
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"0x10",
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"0x20",
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"0x30",
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"0x40",
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"0x50",
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"0x60",
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"0x70",
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"0x07",
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"0x06",
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"0x05",
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"0x04",
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"0x03",
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"0x02",
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"0x01",
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"0x00",
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"0x0f",
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"0x0e",
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"0x0d",
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"0x0c",
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"0x0b",
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"0x0a",
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"0x09",
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"0x08",
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"0x70",
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"0x60",
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"0x50",
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"0x40",
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"0x30",
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"0x20",
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"0x10",
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"0x00",
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"0xf0",
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"0xe0",
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"0xd0",
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"0xc0",
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"0xb0",
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"0xa0",
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"0x90",
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"0x80"
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]
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},
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"OTP_DATA_KEY1" : [ 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7 ],
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"OTP_DATA_KEY1_VALID" : "0x010101",
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"OTP_DATA_KEY2" : [ 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0 ],
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"OTP_DATA_KEY2_VALID" : "0x010101",
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"PAGE30_LOCK0" : "0x4a4a4a"
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}
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}

‎bootloaders/encrypted/privateaes.bin

96 Bytes
Binary file not shown.

‎bootloaders/encrypted/update-key.cmake

+1-1
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@@ -1,7 +1,7 @@
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if (CMAKE_VERSION VERSION_LESS 3.19)
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# Check if keyfile is not the default, and print warning
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file(READ ${CMAKE_CURRENT_LIST_DIR}/privateaes.bin key_file HEX)
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if (NOT ${key_file} STREQUAL "000102030405060708090a0b0c0d0e0f00102030405060708090a0b0c0d0e0f0")
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if (NOT ${key_file} STREQUAL "000102030405060708090a0b0c0d0e0f00102030405060708090a0b0c0d0e0f00f0e0d0c0b0a09080706050403020100f0e0d0c0b0a09080706050403020100008090a0b0c0d0e0f00010203040506078090a0b0c0d0e0f0001020304050607007060504030201000f0e0d0c0b0a09087060504030201000f0e0d0c0b0a09080")
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message(WARNING
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"Encrypted bootloader AES key not updated in otp.json file, as CMake version is < 3.19"
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" - you will need to change the key in otp.json manually and re-run the build"

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