keyfork-shard: base64 encode content instead of base16

Cargo.lock

@@ -341,6 +341,12 @@ version = "0.21.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9d297deb1925b89f2ccc13d7635fa0714f12c87adce1c75356b39ca9b7178567"
 
+[[package]]
+name = "base64"
+version = "0.22.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9475866fec1451be56a3c2400fd081ff546538961565ccb5b7142cbd22bc7a51"
+
 [[package]]
 name = "base64ct"
 version = "1.6.0"
@@ -1497,9 +1503,9 @@ dependencies = [
 
 [[package]]
 name = "iana-time-zone"
-version = "0.1.59"
+version = "0.1.60"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b6a67363e2aa4443928ce15e57ebae94fd8949958fd1223c4cfc0cd473ad7539"
+checksum = "e7ffbb5a1b541ea2561f8c41c087286cc091e21e556a4f09a8f6cbf17b69b141"
 dependencies = [
  "android_system_properties",
  "core-foundation-sys",
@@ -1830,10 +1836,11 @@ dependencies = [
 
 [[package]]
 name = "keyfork-shard"
-version = "0.1.0"
+version = "0.2.0"
 dependencies = [
  "aes-gcm",
  "anyhow",
+ "base64 0.22.0",
  "card-backend",
  "card-backend-pcsc",
  "hkdf",
@@ -2103,9 +2110,9 @@ dependencies = [
 
 [[package]]
 name = "mio"
-version = "0.8.10"
+version = "0.8.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8f3d0b296e374a4e6f3c7b0a1f5a51d748a0d34c85e7dc48fc3fa9a87657fe09"
+checksum = "a4a650543ca06a924e8b371db273b2756685faae30f8487da1b56505a8f78b0c"
 dependencies = [
  "libc",
  "log",
@@ -2886,7 +2893,7 @@ dependencies = [
  "aes",
  "aes-gcm",
  "anyhow",
- "base64",
+ "base64 0.21.7",
  "block-padding",
  "blowfish",
  "buffered-reader",

crates/keyfork-shard/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "keyfork-shard"
-version = "0.1.0"
+version = "0.2.0"
 edition = "2021"
 license = "AGPL-3.0-only"
 
@@ -37,3 +37,4 @@ card-backend-pcsc = { version = "0.5.0", optional = true }
 openpgp-card-sequoia = { version = "0.2.0", optional = true, default-features = false }
 openpgp-card = { version = "0.4.0", optional = true }
 sequoia-openpgp = { version = "1.17.0", optional = true, default-features = false }
+base64 = "0.22.0"

crates/keyfork-shard/src/lib.rs

@@ -7,22 +7,28 @@ use std::{
 };
 
 use aes_gcm::{
-    aead::{consts::U12, Aead, AeadCore, OsRng},
+    aead::{consts::U12, Aead},
     Aes256Gcm, KeyInit, Nonce,
 };
 use hkdf::Hkdf;
 use keyfork_bug::{bug, POISONED_MUTEX};
 use keyfork_mnemonic_util::{English, Mnemonic};
 use keyfork_prompt::{
-    validators::{mnemonic::MnemonicSetValidator, Validator},
+    validators::{
+        mnemonic::{MnemonicSetValidator, MnemonicValidator, WordLength},
+        Validator,
+    },
     Message as PromptMessage, PromptHandler, Terminal,
 };
 use sha2::Sha256;
 use sharks::{Share, Sharks};
 use x25519_dalek::{EphemeralSecret, PublicKey};
+use base64::prelude::{BASE64_STANDARD, Engine};
 
-// 256 bit share encrypted is 49 bytes, couple more bytes before we reach max size
-const ENC_LEN: u8 = 4 * 16;
+// 32-byte share, 1-byte index, 1-byte threshold, 1-byte version == 36 bytes
+// Encrypted, is 52 bytes
+const PLAINTEXT_LENGTH: u8 = 36;
+const ENCRYPTED_LENGTH: u8 = PLAINTEXT_LENGTH + 16;
 
 #[cfg(feature = "openpgp")]
 pub mod openpgp;
@@ -194,7 +200,6 @@ pub trait Format {
         let encrypted_messages = self.parse_shard_file(reader)?;
 
         // establish AES-256-GCM key via ECDH
-        let mut nonce_data: Option<[u8; 12]> = None;
         let mut pubkey_data: Option<[u8; 32]> = None;
 
         // receive remote data via scanning QR code from camera
@@ -204,12 +209,11 @@ pub trait Format {
                 .lock()
                 .expect(bug!(POISONED_MUTEX))
                 .prompt_message(PromptMessage::Text(QRCODE_PROMPT.to_string()))?;
-            if let Ok(Some(hex)) =
+            if let Ok(Some(qrcode_content)) =
                 keyfork_qrcode::scan_camera(std::time::Duration::from_secs(30), 0)
             {
-                let decoded_data = smex::decode(&hex)?;
-                nonce_data = Some(decoded_data[..12].try_into().map_err(|_| InvalidData)?);
-                pubkey_data = Some(decoded_data[12..].try_into().map_err(|_| InvalidData)?)
+                let decoded_data = BASE64_STANDARD.decode(qrcode_content).unwrap();
+                pubkey_data = Some(decoded_data.try_into().map_err(|_| InvalidData)?)
             } else {
                 prompt
                     .lock()
@@ -219,30 +223,23 @@ pub trait Format {
         }
 
         // if QR code scanning failed or was unavailable, read from a set of mnemonics
-        let (nonce, their_pubkey) = match (nonce_data, pubkey_data) {
-            (Some(nonce), Some(pubkey)) => (nonce, pubkey),
-            _ => {
-                let validator = MnemonicSetValidator {
-                    word_lengths: [9, 24],
+        let their_pubkey = match pubkey_data {
+            Some(pubkey) => pubkey,
+            None => {
+                let validator = MnemonicValidator {
+                    word_length: Some(WordLength::Count(24)),
                 };
-                let [nonce_mnemonic, pubkey_mnemonic] = prompt
+                prompt
                     .lock()
                     .expect(bug!(POISONED_MUTEX))
                     .prompt_validated_wordlist::<English, _>(
                         QRCODE_COULDNT_READ,
                         3,
                         validator.to_fn(),
-                    )?;
-
-                let nonce = nonce_mnemonic
+                    )?
                     .as_bytes()
                     .try_into()
-                    .map_err(|_| InvalidData)?;
-                let pubkey = pubkey_mnemonic
-                    .as_bytes()
-                    .try_into()
-                    .map_err(|_| InvalidData)?;
-                (nonce, pubkey)
+                    .map_err(|_| InvalidData)?
             }
         };
 
@@ -253,9 +250,14 @@ pub trait Format {
             .diffie_hellman(&PublicKey::from(their_pubkey))
             .to_bytes();
         let hkdf = Hkdf::<Sha256>::new(None, &shared_secret);
-        let mut hkdf_output = [0u8; 256 / 8];
-        hkdf.expand(&[], &mut hkdf_output)?;
-        let shared_key = Aes256Gcm::new_from_slice(&hkdf_output)?;
+
+        let mut shared_key_data = [0u8; 256 / 8];
+        hkdf.expand(b"key", &mut shared_key_data)?;
+        let shared_key = Aes256Gcm::new_from_slice(&shared_key_data)?;
+
+        let mut nonce_data = [0u8; 12];
+        hkdf.expand(b"nonce", &mut nonce_data)?;
+        let nonce = Nonce::<U12>::from_slice(&nonce_data);
 
         // decrypt a single shard and create the payload
         let (share, threshold) =
@@ -264,49 +266,41 @@ pub trait Format {
         payload.insert(0, HUNK_VERSION);
         payload.insert(1, threshold);
         assert!(
-            payload.len() <= ENC_LEN as usize,
-            "invalid share length (too long, max {ENC_LEN} bytes)"
+            payload.len() < PLAINTEXT_LENGTH as usize,
+            "invalid share length (too long, max {PLAINTEXT_LENGTH} bytes)"
         );
 
-        // encrypt data
-        let nonce = Nonce::<U12>::from_slice(&nonce);
-        let payload_bytes = shared_key.encrypt(nonce, payload.as_slice())?;
-
-        // convert data to a static-size payload
-        // NOTE: Padding length is less than u8::MAX because ENC_LEN < u8::MAX
+        // convert plaintext to static-size payload
         #[allow(clippy::assertions_on_constants)]
         {
-            assert!(ENC_LEN < u8::MAX, "padding byte can be u8");
+            assert!(PLAINTEXT_LENGTH < u8::MAX, "length byte can be u8");
         }
-        #[allow(clippy::cast_possible_truncation)]
-        let mut out_bytes = [payload_bytes.len() as u8; ENC_LEN as usize];
-        assert!(
-            payload_bytes.len() < out_bytes.len(),
-            "encrypted payload larger than acceptable limit"
-        );
-        out_bytes[..payload_bytes.len()].clone_from_slice(&payload_bytes);
 
-        // NOTE: This previously used a single repeated value as the padding byte, but resulted in
-        // difficulty when entering in prompts manually, as one's place could be lost due to
-        // repeated keywords. This is resolved below by having sequentially increasing numbers up to
-        // but not including the last byte.
+        // NOTE: Previous versions of Keyfork Shard would modify the padding bytes to avoid
+        // duplicate mnemonic words. This version does not include that, and instead uses a
+        // repeated length byte.
         #[allow(clippy::cast_possible_truncation)]
-        for (i, byte) in (out_bytes[payload_bytes.len()..(ENC_LEN as usize - 1)])
-            .iter_mut()
-            .enumerate()
-        {
-            *byte = (i % u8::MAX as usize) as u8;
-        }
+        let mut plaintext_bytes = [u8::try_from(payload.len()).expect(bug!(
+            "previously asserted length must be < {PLAINTEXT_LENGTH}",
+            PLAINTEXT_LENGTH = PLAINTEXT_LENGTH
+        )); PLAINTEXT_LENGTH as usize];
+        plaintext_bytes[..payload.len()].clone_from_slice(&payload);
+
+        // encrypt data
+        let encrypted_bytes = shared_key.encrypt(nonce, plaintext_bytes.as_slice())?;
+
+        assert_eq!(encrypted_bytes.len(), ENCRYPTED_LENGTH as usize);
 
         // safety: size of out_bytes is constant and always % 4 == 0
-        let payload_mnemonic = unsafe { Mnemonic::from_raw_bytes(&out_bytes) };
+        let payload_mnemonic = unsafe { Mnemonic::from_raw_bytes(&encrypted_bytes) };
+        dbg!(payload_mnemonic.words().len());
 
         #[cfg(feature = "qrcode")]
         {
             use keyfork_qrcode::{qrencode, ErrorCorrection};
             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) {
+            if let Ok(qrcode) = qrencode(&BASE64_STANDARD.encode(qrcode_data), ErrorCorrection::Highest) {
                 prompt
                     .lock()
                     .expect(bug!(POISONED_MUTEX))
@@ -401,7 +395,7 @@ pub struct InvalidData;
 /// 1 byte: Version
 /// 1 byte: Threshold
 /// Data: &[u8]
-pub(crate) const HUNK_VERSION: u8 = 1;
+pub(crate) const HUNK_VERSION: u8 = 2;
 pub(crate) const HUNK_OFFSET: usize = 2;
 
 const QRCODE_PROMPT: &str = "Press enter, then present QR code to camera.";
@@ -432,17 +426,14 @@ pub fn remote_decrypt(w: &mut impl Write) -> Result<(), Box<dyn std::error::Erro
 
     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_bytes(nonce.as_slice()) };
         let our_key = EphemeralSecret::random();
         let key_mnemonic = Mnemonic::from_bytes(PublicKey::from(&our_key).as_bytes())?;
 
         #[cfg(feature = "qrcode")]
         {
             use keyfork_qrcode::{qrencode, ErrorCorrection};
-            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) {
+            let qrcode_data = key_mnemonic.to_bytes();
+            if let Ok(qrcode) = qrencode(&BASE64_STANDARD.encode(qrcode_data), ErrorCorrection::Highest) {
                 pm.prompt_message(PromptMessage::Text(format!(
                     concat!(
                         "A QR code will be displayed after this prompt. ",
@@ -458,10 +449,9 @@ pub fn remote_decrypt(w: &mut impl Write) -> Result<(), Box<dyn std::error::Erro
         pm.prompt_message(PromptMessage::Text(format!(
             concat!(
                 "Upon request, these words should be sent to shardholder {iter}: ",
-                "{nonce_mnemonic} {key_mnemonic}"
+                "{key_mnemonic}"
             ),
             iter = iter,
-            nonce_mnemonic = nonce_mnemonic,
             key_mnemonic = key_mnemonic,
         )))?;
 
@@ -471,10 +461,10 @@ pub fn remote_decrypt(w: &mut impl Write) -> Result<(), Box<dyn std::error::Erro
         #[cfg(feature = "qrcode")]
         {
             pm.prompt_message(PromptMessage::Text(QRCODE_PROMPT.to_string()))?;
-            if let Ok(Some(hex)) =
+            if let Ok(Some(qrcode_content)) =
                 keyfork_qrcode::scan_camera(std::time::Duration::from_secs(QRCODE_TIMEOUT), 0)
             {
-                let decoded_data = smex::decode(&hex)?;
+                let decoded_data = BASE64_STANDARD.decode(qrcode_content).unwrap();
                 let _ = pubkey_data.insert(decoded_data[..32].try_into().map_err(|_| InvalidData)?);
                 let _ = payload_data.insert(decoded_data[32..].to_vec());
             } else {
@@ -486,7 +476,7 @@ pub fn remote_decrypt(w: &mut impl Write) -> Result<(), Box<dyn std::error::Erro
             (Some(pubkey), Some(payload)) => (pubkey, payload),
             _ => {
                 let validator = MnemonicSetValidator {
-                    word_lengths: [24, 48],
+                    word_lengths: [24, 39],
                 };
 
                 let [pubkey_mnemonic, payload_mnemonic] = pm
@@ -504,14 +494,24 @@ pub fn remote_decrypt(w: &mut impl Write) -> Result<(), Box<dyn std::error::Erro
             }
         };
 
+        assert_eq!(
+            payload.len(),
+            ENCRYPTED_LENGTH as usize,
+            bug!("invalid payload data")
+        );
+
         let shared_secret = our_key.diffie_hellman(&PublicKey::from(pubkey)).to_bytes();
         let hkdf = Hkdf::<Sha256>::new(None, &shared_secret);
-        let mut hkdf_output = [0u8; 256 / 8];
-        hkdf.expand(&[], &mut hkdf_output)?;
-        let shared_key = Aes256Gcm::new_from_slice(&hkdf_output)?;
 
-        let payload =
-            shared_key.decrypt(&nonce, &payload[..payload[payload.len() - 1] as usize])?;
+        let mut shared_key_data = [0u8; 256 / 8];
+        hkdf.expand(b"key", &mut shared_key_data)?;
+        let shared_key = Aes256Gcm::new_from_slice(&shared_key_data)?;
+
+        let mut nonce_data = [0u8; 12];
+        hkdf.expand(b"nonce", &mut nonce_data)?;
+        let nonce = Nonce::<U12>::from_slice(&nonce_data);
+
+        let payload = shared_key.decrypt(nonce, payload.as_slice())?;
         assert_eq!(HUNK_VERSION, payload[0], "Incompatible hunk version");
 
         match &mut iter_count {
@@ -526,7 +526,8 @@ pub fn remote_decrypt(w: &mut impl Write) -> Result<(), Box<dyn std::error::Erro
             }
         }
 
-        shares.push(payload[HUNK_OFFSET..].to_vec());
+        let payload_len = payload.last().expect(bug!("payload should not be empty"));
+        shares.push(payload[HUNK_OFFSET..usize::from(*payload_len)].to_vec());
     }
 
     let shares = shares

crates/keyfork/Cargo.toml

@@ -32,7 +32,7 @@ keyfork-entropy = { version = "0.1.0", path = "../util/keyfork-entropy", registr
 keyfork-mnemonic-util = { version = "0.2.0", path = "../util/keyfork-mnemonic-util", registry = "distrust" }
 keyfork-prompt = { version = "0.1.0", path = "../util/keyfork-prompt", registry = "distrust" }
 keyfork-qrcode = { version = "0.1.0", path = "../qrcode/keyfork-qrcode", default-features = false, registry = "distrust" }
-keyfork-shard = { version = "0.1.0", path = "../keyfork-shard", default-features = false, features = ["openpgp", "openpgp-card", "qrcode"], registry = "distrust" }
+keyfork-shard = { version = "0.2.0", path = "../keyfork-shard", default-features = false, features = ["openpgp", "openpgp-card", "qrcode"], registry = "distrust" }
 smex = { version = "0.1.0", path = "../util/smex", registry = "distrust" }
 
 clap = { version = "4.4.2", features = ["derive", "env", "wrap_help"] }