change the puzzle secret string

boards/dongle/README.md

@@ -20,6 +20,99 @@ Both LEDs are mounted near the USB connector.
 - The Reset button is mounted sideways near the edge of the board that's opposite of the USB connector.
 - The SW1 button is connected to pin P**1**.06. This round-ish button is right next to the RESET button but closer to the USB connector.
 
+## Changing the puzzle secret string
+
+### Create the secret string
+
+Run the `puzzlegen.rs` program on the host to create a new secret string.
+
+``` console
+$ cargo new --bin puzzlegen
+
+$ cp puzzlegen.rs puzzlegen/src/main.rs
+
+$ cd puzzlegen
+$ # or manually modify the Cargo.toml
+$ cargo add rand
+
+$ # update the plaintext in `src/main.rs`
+$ cargo run
+```
+
+Take note of the output; it will look like this:
+
+``` text
+from: [116, 68, 123, 97, 47, 46, 90, 120, 34, 49, 59, 39, 50, 106, 71, 75, 108, 115, 81, 117, 69, 57, 76, 41, 100, 38, 93, 58, 78, 126, 70, 56, 84, 111, 113, 91, 89, 55, 40, 114, 122, 52, 61, 64, 45, 79, 67, 83, 48, 66, 63, 104, 43, 77, 44, 54, 98, 92, 94, 60, 62, 118, 87, 80, 95, 74, 65, 112, 109, 73, 110, 101, 53, 86, 33, 121, 42, 35, 85, 82, 105, 36, 37, 119, 125, 51, 96, 99, 88, 32, 103, 72, 107, 124, 102]
+to: [81, 78, 109, 61, 120, 87, 125, 98, 100, 91, 97, 66, 57, 117, 49, 64, 48, 85, 75, 73, 92, 101, 83, 110, 62, 89, 35, 37, 93, 71, 123, 121, 60, 38, 115, 102, 59, 47, 108, 80, 58, 44, 86, 111, 41, 84, 96, 50, 51, 70, 43, 112, 79, 46, 113, 107, 106, 116, 65, 68, 69, 77, 105, 56, 103, 67, 40, 54, 99, 55, 45, 63, 34, 88, 119, 74, 94, 32, 114, 36, 95, 124, 118, 76, 126, 72, 82, 122, 33, 104, 90, 39, 42, 52, 53]
+secret: "<p=-*Uh5&Ph6=PQ_z_6=Q_-Zh_-h&IPh?cj?>>?>h$IUQhL&P*Up&6w"
+```
+
+### Generate `puzzle.hex`
+
+``` console
+$ git clone --branch dongle-puzzle https://github.com/japaric/embedded2020
+
+$ cd embedded2020/firmware/apps
+```
+
+Copy the `puzzle.rs` from this folder into the `embedded2020/firmware/apps/src/bin` folder.
+
+Update that copy of `puzzle.rs` with the `FROM`, `TO` and `SECRET` data that you got from `puzzlegen`
+
+```` rust
+static FROM: &[u8] = &[
+    116, 68, 123, 97, 47, 46, 90, 120, 34, 49, 59, 39, 50, 106, 71, 75, 108, 115, 81, 117, 69, 57,
+    76, 41, 100, 38, 93, 58, 78, 126, 70, 56, 84, 111, 113, 91, 89, 55, 40, 114, 122, 52, 61, 64,
+    45, 79, 67, 83, 48, 66, 63, 104, 43, 77, 44, 54, 98, 92, 94, 60, 62, 118, 87, 80, 95, 74, 65,
+    112, 109, 73, 110, 101, 53, 86, 33, 121, 42, 35, 85, 82, 105, 36, 37, 119, 125, 51, 96, 99, 88,
+    32, 103, 72, 107, 124, 102,
+];
+
+static TO: &[u8] = &[
+    81, 78, 109, 61, 120, 87, 125, 98, 100, 91, 97, 66, 57, 117, 49, 64, 48, 85, 75, 73, 92, 101,
+    83, 110, 62, 89, 35, 37, 93, 71, 123, 121, 60, 38, 115, 102, 59, 47, 108, 80, 58, 44, 86, 111,
+    41, 84, 96, 50, 51, 70, 43, 112, 79, 46, 113, 107, 106, 116, 65, 68, 69, 77, 105, 56, 103, 67,
+    40, 54, 99, 55, 45, 63, 34, 88, 119, 74, 94, 32, 114, 36, 95, 124, 118, 76, 126, 72, 82, 122,
+    33, 104, 90, 39, 42, 52, 53,
+];
+
+// store the secret rather than the plaintext -- otherwise `strings $elf` will reveal the answer
+static SECRET: &[u8] = b"<p=-*Uh5&Ph6=PQ_z_6=Q_-Zh_-h&IPh?cj?>>?>h$IUQhL&P*Up&6w";
+````
+
+Build the program; this will produce an ELF file.
+
+``` console
+$ cargo build --bin puzzle --release
+```
+
+Convert that ELF file into a .hex file.
+
+``` console
+$ arm-none-eabi-objcopy -O ihex ../target/thumbv7em-none-eabi/release/puzzle puzzle.hex
+```
+
+Test the produced `puzzle.hex` file:
+
+- flash it onto a dongle using the `dongle-flash` host tool. The green LED on the dongle should turn on
+- run the `serial-term` host tool; you should see the following output. `deviceid` will be different
+``` text
+deviceid=d90eedf1978d5fd2 channel=25 TxPower=+8dBm app=puzzle.hex
+```
+- run the `radio-puzzle-solution` program on a DK; it should be able to decrypt the new secret
+- run the `change-channel` host tool to test changing the Dongle's radio channel
+- modify and re-run the `radio-puzzle-solution` program on a DK to solve the puzzle using a the channel you set in the previous step
+
+### Generate `puzzle-nousb-*.hex`
+
+The procedure is similar to the one for generating the `puzzle.hex`. The differences are:
+
+- you copy `puzzle-nousb.rs` into the `embedded2020` repository
+- you also need to change `const CHANNEL` in the `puzzle-nousb.rs` copy
+- you need to produce one hex file per hard-coded radio channel.
+
+Also test these `nousb` .hex files. Note that the green LED won't turn on when the dongle restarts! The green LED will toggle when a new packet is received and the blue LED will turn on when the decoded secret is received. Also, `change-channel` won't work with the `nousb` variants so you can skip that test.
+
 ## References
 
 - [nRF52840 Dongle section on Nordic Semiconductor's info center](https://infocenter.nordicsemi.com/index.jsp?topic=%2Fug_getting_started%2FUG%2Fgs%2Fdevelop_sw.html&cp=1_0_2)

boards/dongle/puzzle-nousb.rs

@@ -9,6 +9,8 @@ use hal::{
 use heapless::{consts, LinearMap};
 use panic_abort as _;
 
+const CHANNEL: Channel = Channel::_26;
+
 static FROM: &[u8] = &[
     // <redacted>
 ];
@@ -22,7 +24,7 @@ static SECRET: &[u8] = b"<redacted>";
 
 #[no_mangle]
 fn main() -> ! {
-    let (mut rtx, mut rrx) = radio::claim(Channel::_26);
+    let (mut rtx, mut rrx) = radio::claim(CHANNEL);
     let led = led::Green;
 
     let mut dict = LinearMap::<_, _, consts::U128>::new();

boards/dongle/puzzlegen.rs

@@ -0,0 +1,35 @@
+// add this to Cargo.toml
+// ``` toml
+// [dependencies]
+// rand = "0.7.3"
+// ```
+
+use std::{collections::HashMap, ops::Range, str};
+
+use rand::prelude::SliceRandom as _;
+
+fn main() {
+    const PRINTABLE_ASCII: Range<u8> = 32..127;
+    // TODO change this
+    let plaintext = b"example text";
+
+    let mut rng = rand::thread_rng();
+    let mut from = PRINTABLE_ASCII.collect::<Vec<_>>();
+    from.shuffle(&mut rng);
+    let mut to = PRINTABLE_ASCII.collect::<Vec<_>>();
+    to.shuffle(&mut rng);
+
+    let mut dict = HashMap::new();
+    for (&from, &to) in from.iter().zip(to.iter()) {
+        dict.insert(from, to);
+    }
+
+    let secret = plaintext.iter().map(|byte| dict[byte]).collect::<Vec<_>>();
+    println!("from: {:?}", from);
+    println!("to: {:?}", to);
+    println!("plaintext: {}", str::from_utf8(plaintext).expect("was not ASCII"));
+    println!(
+        "secret: {:?}",
+        str::from_utf8(&secret).expect("was not ASCII")
+    );
+}