keyfork-shard: add basic oneshot decrypt mechanism

Cargo.lock

@@ -17,6 +17,41 @@ version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f26201604c87b1e01bd3d98f8d5d9a8fcbb815e8cedb41ffccbeb4bf593a35fe"
 
+[[package]]
+name = "aead"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d122413f284cf2d62fb1b7db97e02edb8cda96d769b16e443a4f6195e35662b0"
+dependencies = [
+ "crypto-common",
+ "generic-array",
+]
+
+[[package]]
+name = "aes"
+version = "0.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac1f845298e95f983ff1944b728ae08b8cebab80d684f0a832ed0fc74dfa27e2"
+dependencies = [
+ "cfg-if",
+ "cipher",
+ "cpufeatures",
+]
+
+[[package]]
+name = "aes-gcm"
+version = "0.10.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "831010a0f742e1209b3bcea8fab6a8e149051ba6099432c8cb2cc117dec3ead1"
+dependencies = [
+ "aead",
+ "aes",
+ "cipher",
+ "ctr",
+ "ghash",
+ "subtle",
+]
+
 [[package]]
 name = "ahash"
 version = "0.4.7"
@@ -341,6 +376,16 @@ dependencies = [
  "windows-targets 0.48.5",
 ]
 
+[[package]]
+name = "cipher"
+version = "0.4.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "773f3b9af64447d2ce9850330c473515014aa235e6a783b02db81ff39e4a3dad"
+dependencies = [
+ "crypto-common",
+ "inout",
+]
+
 [[package]]
 name = "clang-sys"
 version = "1.6.1"
@@ -481,9 +526,19 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1bfb12502f3fc46cca1bb51ac28df9d618d813cdc3d2f25b9fe775a34af26bb3"
 dependencies = [
  "generic-array",
+ "rand_core 0.6.4",
  "typenum",
 ]
 
+[[package]]
+name = "ctr"
+version = "0.9.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0369ee1ad671834580515889b80f2ea915f23b8be8d0daa4bbaf2ac5c7590835"
+dependencies = [
+ "cipher",
+]
+
 [[package]]
 name = "curve25519-dalek"
 version = "4.1.0"
@@ -783,6 +838,16 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "ghash"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d930750de5717d2dd0b8c0d42c076c0e884c81a73e6cab859bbd2339c71e3e40"
+dependencies = [
+ "opaque-debug",
+ "polyval",
+]
+
 [[package]]
 name = "gimli"
 version = "0.28.0"
@@ -903,6 +968,15 @@ dependencies = [
  "hashbrown 0.14.1",
 ]
 
+[[package]]
+name = "inout"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a0c10553d664a4d0bcff9f4215d0aac67a639cc68ef660840afe309b807bc9f5"
+dependencies = [
+ "generic-array",
+]
+
 [[package]]
 name = "insta"
 version = "1.31.0"
@@ -1086,11 +1160,13 @@ dependencies = [
 name = "keyfork-shard"
 version = "0.1.0"
 dependencies = [
+ "aes-gcm",
  "anyhow",
  "bincode",
  "card-backend",
  "card-backend-pcsc",
  "keyfork-derive-openpgp",
+ "keyfork-mnemonic-util",
  "keyfork-prompt",
  "openpgp-card",
  "openpgp-card-sequoia",
@@ -1099,6 +1175,7 @@ dependencies = [
  "sharks",
  "smex",
  "thiserror",
+ "x25519-dalek",
 ]
 
 [[package]]
@@ -1426,6 +1503,12 @@ version = "1.18.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "dd8b5dd2ae5ed71462c540258bedcb51965123ad7e7ccf4b9a8cafaa4a63576d"
 
+[[package]]
+name = "opaque-debug"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "624a8340c38c1b80fd549087862da4ba43e08858af025b236e509b6649fc13d5"
+
 [[package]]
 name = "openpgp-card"
 version = "0.4.0"
@@ -1624,6 +1707,18 @@ version = "3.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4503fa043bf02cee09a9582e9554b4c6403b2ef55e4612e96561d294419429f8"
 
+[[package]]
+name = "polyval"
+version = "0.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d52cff9d1d4dee5fe6d03729099f4a310a41179e0a10dbf542039873f2e826fb"
+dependencies = [
+ "cfg-if",
+ "cpufeatures",
+ "opaque-debug",
+ "universal-hash",
+]
+
 [[package]]
 name = "ppv-lite86"
 version = "0.2.17"
@@ -2440,6 +2535,16 @@ version = "0.2.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f962df74c8c05a667b5ee8bcf162993134c104e96440b663c8daa176dc772d8c"
 
+[[package]]
+name = "universal-hash"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fc1de2c688dc15305988b563c3854064043356019f97a4b46276fe734c4f07ea"
+dependencies = [
+ "crypto-common",
+ "subtle",
+]
+
 [[package]]
 name = "untrusted"
 version = "0.9.0"
@@ -2693,6 +2798,18 @@ version = "0.48.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ed94fce61571a4006852b7389a063ab983c02eb1bb37b47f8272ce92d06d9538"
 
+[[package]]
+name = "x25519-dalek"
+version = "2.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fb66477291e7e8d2b0ff1bcb900bf29489a9692816d79874bea351e7a8b6de96"
+dependencies = [
+ "curve25519-dalek",
+ "rand_core 0.6.4",
+ "serde",
+ "zeroize",
+]
+
 [[package]]
 name = "xxhash-rust"
 version = "0.8.7"

keyfork-shard/Cargo.toml

@@ -26,3 +26,6 @@ sharks = "0.5.0"
 smex = { version = "0.1.0", path = "../smex" }
 thiserror = "1.0.50"
 keyfork-prompt = { version = "0.1.0", path = "../keyfork-prompt", optional = true }
+x25519-dalek = { version = "2.0.0", features = ["getrandom"] }
+keyfork-mnemonic-util = { version = "0.1.0", path = "../keyfork-mnemonic-util" }
+aes-gcm = "0.10.3"

keyfork-shard/src/bin/keyfork-shard-decrypt-openpgp.rs

@@ -0,0 +1,128 @@
+use std::{
+    env,
+    fs::File,
+    io::{stdin, stdout},
+    path::{Path, PathBuf},
+    process::ExitCode,
+    str::FromStr,
+};
+
+use aes_gcm::{aead::Aead, aes::cipher::consts::U12, Aes256Gcm, KeyInit, Nonce};
+use x25519_dalek::{EphemeralSecret, PublicKey};
+
+use keyfork_mnemonic_util::{Mnemonic, Wordlist};
+use keyfork_prompt::PromptManager;
+use keyfork_shard::openpgp::{decrypt_one, discover_certs, openpgp::Cert, parse_messages};
+
+type Result<T, E = Box<dyn std::error::Error>> = std::result::Result<T, E>;
+
+fn validate<'a>(
+    messages_file: impl AsRef<Path>,
+    key_discovery: impl Into<Option<&'a str>>,
+) -> Result<(File, Vec<Cert>)> {
+    let key_discovery = key_discovery.into().map(PathBuf::from);
+    key_discovery.as_ref().map(std::fs::metadata).transpose()?;
+
+    // Load certs from path
+    let certs = key_discovery
+        .map(discover_certs)
+        .transpose()?
+        .unwrap_or(vec![]);
+
+    Ok((File::open(messages_file)?, certs))
+}
+
+fn run() -> Result<()> {
+    let mut args = env::args();
+    let program_name = args.next().expect("program name");
+    let args = args.collect::<Vec<_>>();
+    let (messages_file, cert_list) = match args.as_slice() {
+        [messages_file, key_discovery] => validate(messages_file, key_discovery.as_str())?,
+        [messages_file] => validate(messages_file, None)?,
+        _ => panic!("Usage: {program_name} messages_file [key_discovery]"),
+    };
+
+    let mut encrypted_messages = parse_messages(messages_file)?;
+
+    let encrypted_metadata = encrypted_messages
+        .pop_front()
+        .expect("any pgp encrypted message");
+
+    // Receive their key
+
+    let mut pm = PromptManager::new(stdin(), stdout())?;
+    let wordlist = Wordlist::default();
+    let their_words = pm.prompt_wordlist("Their words: ", &wordlist)?;
+    let mut nonce_words = their_words
+        .split_whitespace()
+        .take(9)
+        .peekable();
+    let mut pubkey_words = their_words
+        .split_whitespace()
+        .skip(9)
+        .take(24)
+        .peekable();
+    let mut nonce_mnemonic = String::new();
+    let mut pubkey_mnemonic = String::new();
+    while let Some(word) = nonce_words.next() {
+        nonce_mnemonic.push_str(word);
+        if nonce_words.peek().is_some() {
+            nonce_mnemonic.push(' ');
+        }
+    }
+    while let Some(word) = pubkey_words.next() {
+        pubkey_mnemonic.push_str(word);
+        if pubkey_words.peek().is_some() {
+            pubkey_mnemonic.push(' ');
+        }
+    }
+    let their_key = Mnemonic::from_str(&pubkey_mnemonic)?.entropy();
+    let their_key: [u8; 32] = their_key.try_into().expect("24 words");
+    let their_nonce = Mnemonic::from_str(&nonce_mnemonic)?.entropy();
+    let their_nonce = Nonce::<U12>::from_slice(&their_nonce);
+
+    let our_key = EphemeralSecret::random();
+    let our_mnemonic =
+        Mnemonic::from_entropy(PublicKey::from(&our_key).as_bytes(), Default::default())?;
+    // TODO: Encode using `qrencode -t ansiutf8 -m 2`
+    pm.prompt_message(&format!("Our words: {our_mnemonic}"))?;
+
+    let shared_secret = our_key
+        .diffie_hellman(&PublicKey::from(their_key))
+        .to_bytes();
+
+    let share = decrypt_one(encrypted_messages.into(), &cert_list, encrypted_metadata)?;
+    assert_eq!(share.len(), 65, "non-constant share length");
+    const LEN: u8 = 24 * 3;
+    let mut encrypted_payload = [(LEN - share.len() as u8); LEN as usize];
+    encrypted_payload[..share.len()].copy_from_slice(&share);
+
+    let shared_key = Aes256Gcm::new_from_slice(&shared_secret)?;
+    let bytes = shared_key.encrypt(their_nonce, share.as_slice()).unwrap();
+
+    const ENC_LEN: u8 = 24 * 4;
+    let mut out_bytes = [(ENC_LEN - bytes.len() as u8); ENC_LEN as usize];
+    assert!(bytes.len() < out_bytes.len(), "encrypted payload larger than acceptable limit");
+    out_bytes[..bytes.len()].clone_from_slice(&bytes);
+
+    // safety: size of out_bytes is immutable and always % 32 == 0
+    let mnemonic = unsafe { Mnemonic::from_raw_entropy(&out_bytes, Default::default()) };
+
+    pm.prompt_message(&format!("Our payload: {mnemonic}"))?;
+
+    Ok(())
+}
+
+fn main() -> ExitCode {
+    let result = run();
+    if let Err(e) = result {
+        eprintln!("Error: {e}");
+        let mut source = e.source();
+        while let Some(new_error) = source.take() {
+            eprintln!("Source: {new_error}");
+            source = new_error.source();
+        }
+        return ExitCode::FAILURE;
+    }
+    ExitCode::SUCCESS
+}

keyfork-shard/src/openpgp.rs

@@ -323,15 +323,17 @@ fn decrypt_metadata(
     })
 }
 
-fn decrypt_one(
+pub fn decrypt_one(
     messages: Vec<EncryptedMessage>,
-    keyring: &mut Keyring,
+    certs: &[Cert],
-    manager: &mut SmartcardManager,
     metadata: EncryptedMessage,
 ) -> Result<Vec<u8>> {
     let policy = NullPolicy::new();
 
-    let content = decrypt_metadata(&metadata, &policy, &mut *keyring, &mut *manager)?;
+    let mut keyring = Keyring::new(certs)?;
+    let mut manager = SmartcardManager::new()?;
+
+    let content = decrypt_metadata(&metadata, &policy, &mut keyring, &mut manager)?;
 
     let (_threshold, root_cert, certs) = decode_metadata_v1(&content)?;
 
@@ -341,13 +343,13 @@ fn decrypt_one(
     let mut messages: HashMap<KeyID, EncryptedMessage> =
         HashMap::from_iter(certs.iter().map(|c| c.keyid()).zip(messages));
 
-    let decrypted_messages = decrypt_with_keyring(&mut messages, &certs, &policy, keyring)?;
+    let decrypted_messages = decrypt_with_keyring(&mut messages, &certs, &policy, &mut keyring)?;
 
     if let Some(message) = decrypted_messages.into_values().next() {
         return Ok(message);
     }
 
-    let decrypted_messages = decrypt_with_manager(1, &mut messages, &certs, policy, manager)?;
+    let decrypted_messages = decrypt_with_manager(1, &mut messages, &certs, policy, &mut manager)?;
 
     if let Some(message) = decrypted_messages.into_values().next() {
         return Ok(message);