keyfork-shard: add instructions for sending QR code to operators

crates/keyfork-shard/src/lib.rs

@@ -46,6 +46,8 @@ pub(crate) const HUNK_OFFSET: usize = 2;
 
 const QRCODE_PROMPT: &str = "Press enter, then present QR code to camera.";
 const QRCODE_TIMEOUT: u64 = 60; // One minute
+const QRCODE_COULDNT_READ: &str = "A QR code could not be scanned. Please enter their words: ";
+const QRCODE_ERROR: &str = "Unable to scan a QR code. Falling back to text entry.";
 
 /// Establish ECDH transport for remote operators, receive transport-encrypted shares, decrypt the
 /// shares, and combine them.
@@ -67,8 +69,10 @@ pub fn remote_decrypt(w: &mut impl Write) -> Result<(), Box<dyn std::error::Erro
     let mut shares = vec![];
 
     let mut threshold = 0;
+    let mut iter = 0;
 
     while iter_count.is_none() || iter_count.is_some_and(|i| i > 0) {
+        iter += 1;
         let nonce = Aes256Gcm::generate_nonce(&mut OsRng);
         let nonce_mnemonic =
             unsafe { Mnemonic::from_raw_entropy(nonce.as_slice(), Default::default()) };
@@ -82,12 +86,26 @@ pub fn remote_decrypt(w: &mut impl Write) -> Result<(), Box<dyn std::error::Erro
             let mut qrcode_data = nonce_mnemonic.to_bytes();
             qrcode_data.extend(key_mnemonic.as_bytes());
             if let Ok(qrcode) = qrencode(&smex::encode(&qrcode_data), ErrorCorrection::Highest) {
+                pm.prompt_message(PromptMessage::Text(format!(
+                    concat!(
+                        "A QR code will be displayed after this prompt. ",
+                        "Send the QR code to only shardholder {iter}. ",
+                        "Nobody else should scan this QR code."
+                    ),
+                    iter = iter
+                )))?;
                 pm.prompt_message(PromptMessage::Data(qrcode))?;
             }
         }
 
         pm.prompt_message(PromptMessage::Text(format!(
-            "Our words: {nonce_mnemonic} {key_mnemonic}"
+            concat!(
+                "Upon request, these words should be sent to shardholder {iter}: ",
+                "{nonce_mnemonic} {key_mnemonic}"
+            ),
+            iter = iter,
+            nonce_mnemonic = nonce_mnemonic,
+            key_mnemonic = key_mnemonic,
         )))?;
 
         let mut pubkey_data: Option<[u8; 32]> = None;
@@ -103,9 +121,7 @@ pub fn remote_decrypt(w: &mut impl Write) -> Result<(), Box<dyn std::error::Erro
                 let _ = pubkey_data.insert(decoded_data[..32].try_into().map_err(|_| InvalidData)?);
                 let _ = payload_data.insert(decoded_data[32..].to_vec());
             } else {
-                pm.prompt_message(PromptMessage::Text(
+                pm.prompt_message(PromptMessage::Text(QRCODE_ERROR.to_string()))?;
-                    "Unable to detect QR code, falling back to text".to_string(),
-                ))?;
             };
         }
 
@@ -116,8 +132,12 @@ pub fn remote_decrypt(w: &mut impl Write) -> Result<(), Box<dyn std::error::Erro
                     word_lengths: [24, 48],
                 };
 
-                let [pubkey_mnemonic, payload_mnemonic] =
+                let [pubkey_mnemonic, payload_mnemonic] = pm.prompt_validated_wordlist(
-                    pm.prompt_validated_wordlist("Their words: ", &wordlist, 3, validator.to_fn())?;
+                    QRCODE_COULDNT_READ,
+                    &wordlist,
+                    3,
+                    validator.to_fn(),
+                )?;
                 let pubkey = pubkey_mnemonic
                     .as_bytes()
                     .try_into()

crates/keyfork-shard/src/openpgp.rs

@@ -56,7 +56,10 @@ use smartcard::SmartcardManager;
 const SHARD_METADATA_VERSION: u8 = 1;
 const SHARD_METADATA_OFFSET: usize = 2;
 
-use super::{InvalidData, SharksError, HUNK_VERSION, QRCODE_PROMPT, QRCODE_TIMEOUT};
+use super::{
+    InvalidData, SharksError, HUNK_VERSION, QRCODE_COULDNT_READ, QRCODE_ERROR, QRCODE_PROMPT,
+    QRCODE_TIMEOUT,
+};
 
 // 256 bit share is 49 bytes + some amount of hunk bytes, gives us reasonable padding
 const ENC_LEN: u8 = 4 * 16;
@@ -472,14 +475,14 @@ pub fn decrypt(
     #[cfg(feature = "qrcode")]
     {
         pm.prompt_message(PromptMessage::Text(QRCODE_PROMPT.to_string()))?;
-        if let Ok(Some(hex)) = keyfork_qrcode::scan_camera(std::time::Duration::from_secs(QRCODE_TIMEOUT), 0) {
+        if let Ok(Some(hex)) =
+            keyfork_qrcode::scan_camera(std::time::Duration::from_secs(QRCODE_TIMEOUT), 0)
+        {
             let decoded_data = smex::decode(&hex)?;
             let _ = nonce_data.insert(decoded_data[..12].try_into().map_err(|_| InvalidData)?);
             let _ = pubkey_data.insert(decoded_data[12..].try_into().map_err(|_| InvalidData)?);
         } else {
-            pm.prompt_message(PromptMessage::Text(
+            pm.prompt_message(PromptMessage::Text(QRCODE_ERROR.to_string()))?;
-                "Unable to detect QR code, falling back to text".to_string(),
-            ))?;
         };
     }
 
@@ -490,7 +493,7 @@ pub fn decrypt(
                 word_lengths: [9, 24],
             };
             let [nonce_mnemonic, pubkey_mnemonic] =
-                pm.prompt_validated_wordlist("Their words: ", &wordlist, 3, validator.to_fn())?;
+                pm.prompt_validated_wordlist(QRCODE_COULDNT_READ, &wordlist, 3, validator.to_fn())?;
 
             let nonce = nonce_mnemonic
                 .as_bytes()
@@ -561,12 +564,20 @@ pub fn decrypt(
         let mut qrcode_data = our_pubkey_mnemonic.to_bytes();
         qrcode_data.extend(payload_mnemonic.as_bytes());
         if let Ok(qrcode) = qrencode(&smex::encode(&qrcode_data), ErrorCorrection::Highest) {
+            pm.prompt_message(PromptMessage::Text(
+                concat!(
+                    "A QR code will be displayed after this prompt. ",
+                    "Send the QR code back to the operator combining the shards. ",
+                    "Nobody else should scan this QR code."
+                )
+                .to_string(),
+            ))?;
             pm.prompt_message(PromptMessage::Data(qrcode))?;
         }
     }
 
     pm.prompt_message(PromptMessage::Text(format!(
-        "Our words: {our_pubkey_mnemonic} {payload_mnemonic}"
+        "Upon request, these words should be sent: {our_pubkey_mnemonic} {payload_mnemonic}"
     )))?;
 
     Ok(())