feat(core): recovery_qr generate + unwrap + SVG functions

crates/relicario-core/Cargo.toml

@@ -31,6 +31,6 @@ zstd = { version = "0.13", default-features = false }
 tar = { version = "0.4", default-features = false }
 base64 = "0.22"
 csv = "1"
-qrcode = { version = "0.14", default-features = false }
+qrcode = { version = "0.14", default-features = false, features = ["svg"] }
 
 [dev-dependencies]

crates/relicario-core/src/recovery_qr.rs

@@ -0,0 +1,129 @@
+use chacha20poly1305::{XChaCha20Poly1305, Key, KeyInit, aead::Aead};
+use rand::RngCore;
+use unicode_normalization::UnicodeNormalization;
+use zeroize::Zeroizing;
+use crate::{crypto::KdfParams, error::{RelicarioError, Result}};
+
+const MAGIC: &[u8; 4] = b"RREC";
+const VERSION: u8 = 0x01;
+const PAYLOAD_LEN: usize = 4 + 1 + 32 + 24 + 48; // 109
+
+pub struct RecoveryQrPayload {
+    bytes: [u8; PAYLOAD_LEN],
+}
+
+impl RecoveryQrPayload {
+    pub fn as_bytes(&self) -> &[u8; PAYLOAD_LEN] {
+        &self.bytes
+    }
+}
+
+fn recovery_kdf_input(passphrase: &str) -> Vec<u8> {
+    let nfc: String = passphrase.nfc().collect();
+    let nfc_bytes = nfc.as_bytes();
+    let prefix = b"relicario-recovery-v1\0";
+    let mut input = Vec::with_capacity(prefix.len() + 8 + nfc_bytes.len());
+    input.extend_from_slice(prefix);
+    input.extend_from_slice(&(nfc_bytes.len() as u64).to_be_bytes());
+    input.extend_from_slice(nfc_bytes);
+    input
+}
+
+fn production_params() -> KdfParams {
+    KdfParams { argon2_m: 65536, argon2_t: 3, argon2_p: 4 }
+}
+
+fn derive_wrap_key(
+    passphrase: &str,
+    kdf_salt: &[u8; 32],
+    params: &KdfParams,
+) -> Result<Zeroizing<[u8; 32]>> {
+    let input = recovery_kdf_input(passphrase);
+    crate::crypto::derive_master_key_raw(&input, kdf_salt, params)
+}
+
+pub fn generate_recovery_qr(
+    passphrase: &str,
+    image_secret: &[u8; 32],
+) -> Result<RecoveryQrPayload> {
+    generate_recovery_qr_with_params(passphrase, image_secret, &production_params())
+}
+
+#[doc(hidden)]
+pub fn generate_recovery_qr_with_params(
+    passphrase: &str,
+    image_secret: &[u8; 32],
+    params: &KdfParams,
+) -> Result<RecoveryQrPayload> {
+    let mut kdf_salt = [0u8; 32];
+    rand::rngs::OsRng.fill_bytes(&mut kdf_salt);
+
+    let mut wrap_nonce = [0u8; 24];
+    rand::rngs::OsRng.fill_bytes(&mut wrap_nonce);
+
+    let wrap_key = derive_wrap_key(passphrase, &kdf_salt, params)?;
+    let cipher = XChaCha20Poly1305::new(Key::from_slice(wrap_key.as_ref()));
+    let nonce = chacha20poly1305::XNonce::from_slice(&wrap_nonce);
+    let ciphertext = cipher.encrypt(nonce, image_secret.as_ref())
+        .map_err(|_| RelicarioError::RecoveryQr("wrap encrypt failed".into()))?;
+
+    let mut bytes = [0u8; PAYLOAD_LEN];
+    let mut pos = 0;
+    bytes[pos..pos+4].copy_from_slice(MAGIC);     pos += 4;
+    bytes[pos] = VERSION;                           pos += 1;
+    bytes[pos..pos+32].copy_from_slice(&kdf_salt); pos += 32;
+    bytes[pos..pos+24].copy_from_slice(&wrap_nonce); pos += 24;
+    bytes[pos..pos+48].copy_from_slice(&ciphertext);
+
+    Ok(RecoveryQrPayload { bytes })
+}
+
+pub fn unwrap_recovery_qr(
+    payload_bytes: &[u8],
+    passphrase: &str,
+) -> Result<Zeroizing<[u8; 32]>> {
+    unwrap_recovery_qr_with_params(payload_bytes, passphrase, &production_params())
+}
+
+#[doc(hidden)]
+pub fn unwrap_recovery_qr_with_params(
+    payload_bytes: &[u8],
+    passphrase: &str,
+    params: &KdfParams,
+) -> Result<Zeroizing<[u8; 32]>> {
+    if payload_bytes.len() != PAYLOAD_LEN {
+        return Err(RelicarioError::RecoveryQr(
+            format!("payload must be {PAYLOAD_LEN} bytes, got {}", payload_bytes.len())
+        ));
+    }
+    if &payload_bytes[0..4] != MAGIC {
+        return Err(RelicarioError::RecoveryQr("bad magic".into()));
+    }
+    if payload_bytes[4] != VERSION {
+        return Err(RelicarioError::RecoveryQr(
+            format!("unsupported version 0x{:02x}", payload_bytes[4])
+        ));
+    }
+    let kdf_salt: &[u8; 32] = payload_bytes[5..37].try_into().unwrap();
+    let wrap_nonce = &payload_bytes[37..61];
+    let ciphertext = &payload_bytes[61..109];
+
+    let wrap_key = derive_wrap_key(passphrase, kdf_salt, params)?;
+    let cipher = XChaCha20Poly1305::new(Key::from_slice(wrap_key.as_ref()));
+    let nonce = chacha20poly1305::XNonce::from_slice(wrap_nonce);
+    let plaintext = cipher.decrypt(nonce, ciphertext)
+        .map_err(|_| RelicarioError::Decrypt)?;
+
+    let mut out = Zeroizing::new([0u8; 32]);
+    out.copy_from_slice(&plaintext);
+    Ok(out)
+}
+
+pub fn recovery_qr_to_svg(payload: &RecoveryQrPayload) -> String {
+    use qrcode::{QrCode, EcLevel};
+    let code = QrCode::with_error_correction_level(payload.bytes.as_ref(), EcLevel::M)
+        .expect("109-byte payload always fits QR version 6");
+    code.render::<qrcode::render::svg::Color>()
+        .min_dimensions(140, 140)
+        .build()
+}