//! COSE key parsing and signature verification (ES256 / RS256) via `ring`,
//! plus base64url helpers and CSPRNG challenge generation.
//!
//! # Security
//!
//! - All cryptographic primitives come from `ring` (constant-time ECDSA/RSA
//! verification). This crate contains no hand-rolled cryptography; the only
//! custom encoding is RFC 5280 DER *wrapping* of already-validated RSA
//! modulus/exponent byte strings, which never touches secret material.
//! - Signature verification is constant-result: on failure the payload and
//! signature are discarded and only an error variant is returned.
use crate::error::WebauthnError;
/// Parsed COSE public key (EC2 or RSA).
#[derive(Debug, Clone)]
pub enum CosePublicKey {
/// Elliptic-curve (P-256) key with affine coordinates `x` and `y`.
Ec2 {
/// X coordinate, big-endian, 32 bytes for P-256.
x: Vec<u8>,
/// Y coordinate, big-endian, 32 bytes for P-256.
y: Vec<u8>,
},
/// RSA key with modulus `n` and public exponent `e`.
Rsa {
/// RSA modulus, big-endian.
n: Vec<u8>,
/// RSA public exponent, big-endian (typically 0x010001).
e: Vec<u8>,
},
}
/// COSE key type: Octet Key Pair (Ed25519 et al.). Not supported.
pub const COSE_KTY_OKP: i64 = 1;
/// COSE key type: Elliptic-Curve key pair with x/y coordinates.
pub const COSE_KTY_EC2: i64 = 2;
/// COSE key type: RSA key.
pub const COSE_KTY_RSA: i64 = 3;
/// COSE algorithm: ECDSA w/ SHA-256 on P-256.
pub const COSE_ALG_ES256: i32 = -7;
/// COSE algorithm: RSASSA-PKCS1-v1_5 w/ SHA-256.
pub const COSE_ALG_RS256: i32 = -257;
/// COSE key map parameter label: key type (`kty`).
const COSE_KEY_KTY: i64 = 1;
/// COSE key map parameter label: algorithm (`alg`).
const COSE_KEY_ALG: i64 = 2;
/// COSE key map parameter label: curve (EC2) or modulus `n` (RSA).
const COSE_KEY_CRV_N: i64 = -1;
/// COSE key map parameter label: x coordinate (EC2) or exponent `e` (RSA).
const COSE_KEY_X_E: i64 = -2;
/// COSE key map parameter label: y coordinate (EC2).
const COSE_KEY_Y: i64 = -3;
/// COSE curve identifier: NIST P-256 (secp256r1).
const COSE_CRV_P256: i64 = 1;
/// Parse a CBOR integer from a value, handling both positive and negative.
fn cbor_i64(val: &ciborium::Value) -> Option<i64> {
use ciborium::Value;
match val {
Value::Integer(i) => (*i).try_into().ok(),
_ => None,
}
}
/// Extract a CBOR byte string from a value.
///
/// # Security note
///
/// Deliberately lenient: a CBOR text string is accepted and re-interpreted as
/// its UTF-8 byte representation. This tolerates non-conformant authenticators
/// that encode binary fields as text. Length/format validation of the extracted
/// bytes happens downstream (`ring` rejects malformed keys at verify time).
pub fn cbor_bytes(val: &ciborium::Value) -> Option<Vec<u8>> {
use ciborium::Value;
match val {
Value::Bytes(b) => Some(b.clone()),
Value::Text(t) => Some(t.as_bytes().to_vec()),
_ => None,
}
}
/// Parse a CBOR map into ordered `(i64, Value)` entries.
///
/// Returns `None` if the value is not a map or any key is not an integer.
/// Duplicate keys are preserved in order; last occurrence wins when consumers
/// iterate and assign, matching CBOR common practice.
pub fn cbor_map_entries(val: &ciborium::Value) -> Option<Vec<(i64, ciborium::Value)>> {
use ciborium::Value;
match val {
Value::Map(entries) => {
let mut result = Vec::with_capacity(entries.len());
for (k, v) in entries {
let key = cbor_i64(k)?;
result.push((key, v.clone()));
}
Some(result)
}
_ => None,
}
}
/// Parse a COSE key from its CBOR encoding (RFC 9052).
///
/// Supports EC2/P-256 (`kty = 2`, `crv = 1`) and RSA (`kty = 3`). OKP keys
/// return [`WebauthnError::UnsupportedAlgorithm`]; unknown key types return
/// [`WebauthnError::VerificationFailed`].
///
/// # Security notes / threat assumptions
///
/// - `cose_bytes` is attacker-controlled input (it arrives inside authenticator
/// data). Parsing must never panic on arbitrary bytes; malformed input always
/// yields `Err`.
/// - The returned `alg` is whatever the key declares. Callers must check it is
/// one of [`COSE_ALG_ES256`] / [`COSE_ALG_RS256`] *and* pass it to
/// [`verify_cose_signature`], which cross-checks key type against algorithm
/// (e.g. an RSA key claiming `alg = -7` is rejected).
/// - Coordinate/modulus lengths are not pre-validated here; `ring` rejects
/// invalid lengths during signature verification.
///
/// # Requirements
/// REQ-WA-003, REQ-WA-100, REQ-WA-107
///
/// Returns the COSE algorithm identifier and the parsed key components.
pub fn parse_cose_key(cose_bytes: &[u8]) -> Result<(i32, CosePublicKey), WebauthnError> {
use ciborium::Value;
let key_val: Value = ciborium::de::from_reader(cose_bytes).map_err(|e| {
WebauthnError::VerificationFailed(format!("COSE key CBOR parse error: {e}"))
})?;
let entries = cbor_map_entries(&key_val).ok_or_else(|| {
WebauthnError::VerificationFailed("COSE key is not a CBOR map".to_string())
})?;
let mut kty: Option<i64> = None;
let mut alg: Option<i32> = None;
let mut crv: Option<i64> = None;
let mut x: Option<Vec<u8>> = None;
let mut y: Option<Vec<u8>> = None;
let mut n: Option<Vec<u8>> = None;
let mut e: Option<Vec<u8>> = None;
for (label, val) in &entries {
match *label {
COSE_KEY_KTY => kty = cbor_i64(val),
COSE_KEY_ALG => alg = cbor_i64(val).map(|v| v as i32),
COSE_KEY_CRV_N => match kty {
Some(COSE_KTY_RSA) => n = cbor_bytes(val),
_ => crv = cbor_i64(val),
},
COSE_KEY_X_E => match kty {
Some(COSE_KTY_RSA) => e = cbor_bytes(val),
_ => x = cbor_bytes(val),
},
COSE_KEY_Y => y = cbor_bytes(val),
_ => {}
}
}
let kty =
kty.ok_or_else(|| WebauthnError::VerificationFailed("COSE key missing 'kty'".to_string()))?;
let alg =
alg.ok_or_else(|| WebauthnError::VerificationFailed("COSE key missing 'alg'".to_string()))?;
match kty {
COSE_KTY_EC2 => {
let crv = crv.ok_or_else(|| {
WebauthnError::VerificationFailed("EC2 key missing 'crv'".to_string())
})?;
if crv != COSE_CRV_P256 {
return Err(WebauthnError::UnsupportedAlgorithm(alg));
}
let x = x.ok_or_else(|| {
WebauthnError::VerificationFailed("EC2 key missing 'x'".to_string())
})?;
let y = y.ok_or_else(|| {
WebauthnError::VerificationFailed("EC2 key missing 'y'".to_string())
})?;
Ok((alg, CosePublicKey::Ec2 { x, y }))
}
COSE_KTY_RSA => {
let n = n.ok_or_else(|| {
WebauthnError::VerificationFailed("RSA key missing 'n'".to_string())
})?;
let e = e.ok_or_else(|| {
WebauthnError::VerificationFailed("RSA key missing 'e'".to_string())
})?;
Ok((alg, CosePublicKey::Rsa { n, e }))
}
COSE_KTY_OKP => Err(WebauthnError::UnsupportedAlgorithm(alg)),
other => Err(WebauthnError::VerificationFailed(format!(
"Unsupported COSE key type: {other}"
))),
}
}
/// Verify a COSE signature using the parsed public key.
///
/// # Security notes / threat assumptions
///
/// - `alg` is matched strictly: `ES256` requires an [`CosePublicKey::Ec2`]
/// key, `RS256` requires [`CosePublicKey::Rsa`]; any mismatch is an error,
/// never a fallback.
/// - `signed_data` and `signature` are attacker-controlled. Verification uses
/// `ring`'s constant-time implementations
/// (`ECDSA_P256_SHA256_FIXED`, `RSA_PKCS1_2048_8192_SHA256`).
/// - RSA keys smaller than 2048 bits are rejected by `ring`'s
/// `RSA_PKCS1_2048_8192_SHA256` parameters.
///
/// # Requirements
/// REQ-WA-106, REQ-WA-107
///
/// Returns `Ok(())` if and only if the signature verifies over `signed_data`.
pub fn verify_cose_signature(
alg: i32,
public_key: &CosePublicKey,
signed_data: &[u8],
signature: &[u8],
) -> Result<(), WebauthnError> {
use ring::signature;
match alg {
COSE_ALG_ES256 => {
let CosePublicKey::Ec2 { x, y } = public_key else {
return Err(WebauthnError::VerificationFailed(
"EC2 key expected for ES256".to_string(),
));
};
let mut public_key_bytes = Vec::with_capacity(1 + x.len() + y.len());
public_key_bytes.push(0x04);
public_key_bytes.extend_from_slice(x);
public_key_bytes.extend_from_slice(y);
let public_key = signature::UnparsedPublicKey::new(
&signature::ECDSA_P256_SHA256_FIXED,
&public_key_bytes,
);
public_key
.verify(signed_data, signature)
.map_err(|_| WebauthnError::SignatureVerificationFailed)?;
Ok(())
}
COSE_ALG_RS256 => {
let CosePublicKey::Rsa { n, e } = public_key else {
return Err(WebauthnError::VerificationFailed(
"RSA key expected for RS256".to_string(),
));
};
let rsa_public_key = RsaPublicKeyDer { n, e };
let der_bytes = rsa_public_key.to_der()?;
let public_key = signature::UnparsedPublicKey::new(
&signature::RSA_PKCS1_2048_8192_SHA256,
&der_bytes,
);
public_key
.verify(signed_data, signature)
.map_err(|_| WebauthnError::SignatureVerificationFailed)?;
Ok(())
}
other => Err(WebauthnError::UnsupportedAlgorithm(other)),
}
}
/// ASN.1 DER (PKCS#1 RFC 8017 `RSAPublicKey`) encoding helper for RSA
/// public keys.
struct RsaPublicKeyDer<'a> {
n: &'a [u8],
e: &'a [u8],
}
impl RsaPublicKeyDer<'_> {
/// Encode modulus/exponent into a DER `RSAPublicKey` structure:
/// `SEQUENCE { modulus INTEGER, publicExponent INTEGER }`.
///
/// This is the encoding `ring`'s RSA signature verifiers parse
/// (`ring::rsa::parse_public_key`) — NOT an RFC 5280
/// `SubjectPublicKeyInfo`.
fn to_der(&self) -> Result<Vec<u8>, WebauthnError> {
let mut der = Vec::new();
Self::encode_integer(&mut der, self.n);
Self::encode_integer(&mut der, self.e);
Self::encode_sequence_in_place(&mut der);
Ok(der)
}
/// DER-encode an INTEGER from a big-endian byte string.
///
/// Strips leading zero octets and prepends a single `0x00` when the
/// high bit is set, per DER INTEGER positivity rules (a form ring's
/// DER parser accepts).
fn encode_integer(buf: &mut Vec<u8>, value: &[u8]) {
let start = value
.iter()
.position(|&b| b != 0)
.unwrap_or(value.len().saturating_sub(1));
let v = value.get(start..).unwrap_or(&[]);
if v.first().is_some_and(|&b| b & 0x80 != 0) {
buf.push(0x02);
Self::encode_length(buf, v.len() + 1);
buf.push(0x00);
buf.extend_from_slice(v);
} else {
buf.push(0x02);
Self::encode_length(buf, v.len());
buf.extend_from_slice(v);
}
}
/// Wrap the existing buffer content in a SEQUENCE by shifting right.
fn encode_sequence_in_place(buf: &mut Vec<u8>) {
let content_len = buf.len();
let header_len = if content_len < 0x80 {
2
} else if content_len < 0x100 {
3
} else {
4
};
buf.resize(content_len + header_len, 0);
buf.copy_within(..content_len, header_len);
if let Some(tag) = buf.first_mut() {
*tag = 0x30;
}
Self::encode_length_at(buf, 1, content_len);
}
/// DER-encode a length octet string at the end of `buf`.
fn encode_length(buf: &mut Vec<u8>, len: usize) {
if len < 0x80 {
buf.push(len as u8);
} else if len < 0x100 {
buf.push(0x81);
buf.push(len as u8);
} else {
buf.push(0x82);
buf.push((len >> 8) as u8);
buf.push((len & 0xFF) as u8);
}
}
/// DER-encode a length octet string at `offset` in `buf`.
///
/// INVARIANT: the caller guarantees `buf.len() >= offset + needed`,
/// where `needed` is 1, 2, or 3 depending on `len` (callers size the
/// buffer via the matching `header_len` computation before calling).
/// The direct indexing below is therefore in-bounds by construction.
#[allow(clippy::indexing_slicing)]
fn encode_length_at(buf: &mut [u8], offset: usize, len: usize) {
if len < 0x80 {
buf[offset] = len as u8;
} else if len < 0x100 {
buf[offset] = 0x81;
buf[offset + 1] = len as u8;
} else {
buf[offset] = 0x82;
buf[offset + 1] = (len >> 8) as u8;
buf[offset + 2] = (len & 0xFF) as u8;
}
}
}
/// Convert a COSE algorithm ID to a human-readable name.
pub fn alg_to_name(alg: i32) -> &'static str {
match alg {
COSE_ALG_ES256 => "ES256",
COSE_ALG_RS256 => "RS256",
_ => "unknown",
}
}
/// Generate 32 random bytes (256 bits of entropy) for a `WebAuthn` challenge.
///
/// Uses the operating system CSPRNG via `ring::rand::SystemRandom`.
///
/// # Security notes
///
/// Challenges MUST come from a cryptographically secure source. If the OS
/// entropy source fails, this function panics rather than emit predictable
/// challenges (a failed CSPRNG is unrecoverable for security purposes).
///
/// # Requirements
/// REQ-WA-110
pub fn generate_challenge_bytes() -> Vec<u8> {
use ring::rand::SecureRandom;
let mut bytes = [0u8; 32];
// INVARIANT: a failed OS CSPRNG is unrecoverable for security purposes
// (documented above) — panicking is the deliberate, correct behavior.
#[allow(clippy::expect_used)]
ring::rand::SystemRandom::new()
.fill(&mut bytes)
.expect("OS CSPRNG unavailable; cannot generate secure challenge");
bytes.to_vec()
}
/// Base64url encode (RFC 4648 §5, no padding), as required by the `WebAuthn`
/// JSON serialization conventions.
pub fn base64_encode_urlsafe(data: &[u8]) -> String {
use base64::Engine;
base64::engine::general_purpose::URL_SAFE_NO_PAD.encode(data)
}
/// Base64url decode (RFC 4648 §5, no padding required; standard alphabet with
/// padding is also accepted by the engine's forgiving handling).
///
/// Returns [`WebauthnError::VerificationFailed`] on malformed input.
///
/// # Requirements
/// REQ-WA-004, REQ-WA-118
pub fn base64_decode_urlsafe(data: &str) -> Result<Vec<u8>, WebauthnError> {
use base64::Engine;
base64::engine::general_purpose::URL_SAFE_NO_PAD
.decode(data)
.map_err(|e| WebauthnError::VerificationFailed(format!("base64 decode error: {e}")))
}
// Tests exercise failure paths and invariants directly; unwrap/expect,
// slicing, and panicking asserts are acceptable here — violations
// surface as test failures, not production panics.
#[allow(
clippy::unwrap_used,
clippy::expect_used,
clippy::indexing_slicing,
clippy::panic
)]
#[cfg(test)]
pub(crate) mod tests {
use super::*;
/// Build a COSE EC2/P-256 key map around the given coordinates.
pub(crate) fn build_cose_ec2_key(x: &[u8], y: &[u8]) -> Vec<u8> {
use ciborium::Value;
let map = vec![
(Value::Integer(1.into()), Value::Integer(2.into())),
(Value::Integer(2.into()), Value::Integer((-7).into())),
(Value::Integer((-1).into()), Value::Integer(1.into())),
(Value::Integer((-2).into()), Value::Bytes(x.to_vec())),
(Value::Integer((-3).into()), Value::Bytes(y.to_vec())),
];
let mut buf = Vec::new();
ciborium::ser::into_writer(&Value::Map(map), &mut buf).unwrap();
buf
}
/// Build a COSE RSA key map around the given modulus/exponent.
pub(crate) fn build_cose_rsa_key(n: &[u8], e: &[u8]) -> Vec<u8> {
use ciborium::Value;
let map = vec![
(Value::Integer(1.into()), Value::Integer(3.into())),
(Value::Integer(2.into()), Value::Integer((-257).into())),
(Value::Integer((-1).into()), Value::Bytes(n.to_vec())),
(Value::Integer((-2).into()), Value::Bytes(e.to_vec())),
];
let mut buf = Vec::new();
ciborium::ser::into_writer(&Value::Map(map), &mut buf).unwrap();
buf
}
#[test]
fn test_parse_cose_ec2_key() {
let x = vec![0xAA; 32];
let y = vec![0xBB; 32];
let cose_key = build_cose_ec2_key(&x, &y);
let (alg, key) = parse_cose_key(&cose_key).unwrap();
assert_eq!(alg, -7);
match key {
CosePublicKey::Ec2 { x: kx, y: ky } => {
assert_eq!(kx, x);
assert_eq!(ky, y);
}
_ => panic!("Expected EC2 key"),
}
}
#[test]
fn test_parse_cose_rsa_key() {
let n = vec![0xAA; 256];
let e = vec![0x01, 0x00, 0x01];
let cose_key = build_cose_rsa_key(&n, &e);
let (alg, key) = parse_cose_key(&cose_key).unwrap();
assert_eq!(alg, -257);
match key {
CosePublicKey::Rsa { n: kn, e: ke } => {
assert_eq!(kn, n);
assert_eq!(ke, e);
}
_ => panic!("Expected RSA key"),
}
}
#[test]
fn test_parse_cose_key_not_a_map() {
let buf = [0x00u8]; // CBOR integer 0
let result = parse_cose_key(&buf);
assert!(matches!(result, Err(WebauthnError::VerificationFailed(_))));
}
#[test]
fn test_parse_cose_key_missing_kty() {
use ciborium::Value;
let map = vec![(Value::Integer(2.into()), Value::Integer((-7).into()))];
let mut buf = Vec::new();
ciborium::ser::into_writer(&Value::Map(map), &mut buf).unwrap();
let result = parse_cose_key(&buf);
assert!(matches!(result, Err(WebauthnError::VerificationFailed(_))));
}
#[test]
fn test_parse_cose_key_okp_unsupported() {
use ciborium::Value;
let map = vec![
(Value::Integer(1.into()), Value::Integer(1.into())),
(Value::Integer(2.into()), Value::Integer((-8).into())),
];
let mut buf = Vec::new();
ciborium::ser::into_writer(&Value::Map(map), &mut buf).unwrap();
let result = parse_cose_key(&buf);
assert!(matches!(
result,
Err(WebauthnError::UnsupportedAlgorithm(-8))
));
}
#[test]
fn test_verify_cose_signature_es256() {
use ring::signature::{EcdsaKeyPair, KeyPair as _, ECDSA_P256_SHA256_FIXED_SIGNING};
let rng = ring::rand::SystemRandom::new();
let pkcs8 = EcdsaKeyPair::generate_pkcs8(&ECDSA_P256_SHA256_FIXED_SIGNING, &rng).unwrap();
let key_pair =
EcdsaKeyPair::from_pkcs8(&ECDSA_P256_SHA256_FIXED_SIGNING, pkcs8.as_ref(), &rng)
.unwrap();
let public_key_bytes = key_pair.public_key().as_ref().to_vec();
let x = public_key_bytes[1..33].to_vec();
let y = public_key_bytes[33..65].to_vec();
let cose_key = CosePublicKey::Ec2 { x, y };
let message = b"test message for WebAuthn";
let signature = key_pair.sign(&rng, message).unwrap();
let result = verify_cose_signature(COSE_ALG_ES256, &cose_key, message, signature.as_ref());
assert!(result.is_ok());
let wrong_result = verify_cose_signature(
COSE_ALG_ES256,
&cose_key,
b"wrong message",
signature.as_ref(),
);
assert!(matches!(
wrong_result,
Err(WebauthnError::SignatureVerificationFailed)
));
}
#[test]
fn test_verify_cose_signature_alg_key_type_mismatch() {
// RSA key material presented with alg = ES256 must be rejected.
let n = vec![0xAA; 256];
let e = vec![0x01, 0x00, 0x01];
let cose_key = build_cose_rsa_key(&n, &e);
let (alg, key) = parse_cose_key(&cose_key).unwrap();
assert_eq!(alg, -257);
let mismatch = verify_cose_signature(COSE_ALG_ES256, &key, b"data", &[0u8; 64]);
assert!(matches!(
mismatch,
Err(WebauthnError::VerificationFailed(_))
));
}
#[test]
fn test_verify_cose_signature_rs256() {
let n = vec![
0xC0, 0xE9, 0x5A, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00,
];
let e = vec![0x01, 0x00, 0x01];
let cose_key = build_cose_rsa_key(&n, &e);
let (alg, key) = parse_cose_key(&cose_key).unwrap();
assert_eq!(alg, -257);
match key {
CosePublicKey::Rsa { n: kn, e: ke } => {
assert_eq!(kn, n);
assert_eq!(ke, e);
}
_ => panic!("Expected RSA key"),
}
let rsa_key = RsaPublicKeyDer { n: &n, e: &e };
let der = rsa_key.to_der().unwrap();
assert_eq!(der[0], 0x30);
assert!(der.len() > 40);
}
#[test]
fn test_generate_challenge_bytes_length() {
let bytes = generate_challenge_bytes();
assert_eq!(bytes.len(), 32);
}
#[test]
fn test_generate_challenge_bytes_not_all_zero() {
// 256 zero bits from a CSPRNG is ~2^-256; treat as failure.
let bytes = generate_challenge_bytes();
assert!(bytes.iter().any(|&b| b != 0));
}
#[test]
fn test_base64_roundtrip() {
let original = b"hello world";
let encoded = base64_encode_urlsafe(original);
let decoded = base64_decode_urlsafe(&encoded).unwrap();
assert_eq!(decoded, original);
}
#[test]
fn test_base64_decode_urlsafe_invalid() {
let result = base64_decode_urlsafe("NOT_VALID_BASE64!!!");
assert!(result.is_err());
}
#[test]
fn test_base64_encode_decode_empty() {
let encoded = base64_encode_urlsafe(b"");
let decoded = base64_decode_urlsafe(&encoded).unwrap();
assert!(decoded.is_empty());
}
#[test]
fn test_cbor_bytes_from_text_is_lenient() {
use ciborium::Value;
let v = Value::Text("abc".to_string());
assert_eq!(cbor_bytes(&v), Some(b"abc".to_vec()));
let v = Value::Null;
assert_eq!(cbor_bytes(&v), None);
}
/// REQ-WA-202: DER INTEGER encoding must handle the all-zero value
/// (single 0x00 octet), strip leading zeros, and prepend 0x00 for
/// high-bit-set values — all without panicking.
#[test]
fn der_integer_encoding_edge_cases() {
let mut buf = Vec::new();
RsaPublicKeyDer::encode_integer(&mut buf, &[0u8; 8]);
assert_eq!(buf, vec![0x02, 0x01, 0x00]);
buf.clear();
buf.clear();
// High-bit-set value: a necessary positive-marker 0x00 is prepended.
RsaPublicKeyDer::encode_integer(&mut buf, &[0x80, 0x00]);
assert_eq!(buf, vec![0x02, 0x03, 0x00, 0x80, 0x00]);
buf.clear();
RsaPublicKeyDer::encode_integer(&mut buf, &[0x00, 0x00, 0x7F]);
assert_eq!(buf, vec![0x02, 0x01, 0x7F]);
buf.clear();
// Empty modulus degenerates to a zero-length INTEGER (malformed DER);
// the encoder stays total and `ring` rejects the key at verify time.
RsaPublicKeyDer::encode_integer(&mut buf, &[]);
assert_eq!(buf, vec![0x02, 0x00]);
}
// ---- error paths of parse_cose_key / verify_cose_signature ----
/// Fixed 2048-bit RSA test key (PKCS#8 DER, base64). ring cannot
/// generate RSA keys, so the fixture is pre-generated with openssl.
pub(crate) const RSA_PKCS8_B64: &str = "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";
/// Decode a DER TLV at `i`; returns `(content, rest)`.
fn der_tlv(i: &[u8]) -> (&[u8], &[u8]) {
let l0 = *i.get(1).unwrap();
let (header, len) = if l0 < 0x80 {
(2usize, l0 as usize)
} else {
let n = (l0 & 0x7F) as usize;
let mut len = 0usize;
for b in &i[2..2 + n] {
len = (len << 8) | *b as usize;
}
(2 + n, len)
};
(&i[header..header + len], &i[header + len..])
}
/// (modulus, exponent, PKCS#8 DER) for the fixed RSA test key.
pub(crate) fn rsa_test_material() -> (Vec<u8>, Vec<u8>, Vec<u8>) {
use base64::Engine as _;
let pkcs8 = base64::engine::general_purpose::STANDARD
.decode(RSA_PKCS8_B64)
.unwrap();
// PrivateKeyInfo ::= SEQ { version, algorithm, OCTET STRING {
// RSAPrivateKey ::= SEQ { version, n, e, ... } } }
let (info, _) = der_tlv(&pkcs8);
let (_version, rest) = der_tlv(info);
let (_algorithm, rest) = der_tlv(rest);
let (octet, _) = der_tlv(rest);
let (rsa_key, _) = der_tlv(octet);
let (_version, rest) = der_tlv(rsa_key);
let (n, rest) = der_tlv(rest);
let (e, _) = der_tlv(rest);
(n.to_vec(), e.to_vec(), pkcs8)
}
/// Minimal-encoding SPKI for the fixed RSA test key, as ring's RSA
/// verifier requires (see `RsaPublicKeyDer::encode_integer`).
pub(crate) fn rsa_test_spki() -> Vec<u8> {
let (n, e, _) = rsa_test_material();
RsaPublicKeyDer { n: &n, e: &e }.to_der().unwrap()
}
fn cose_key_from(entries: Vec<(i64, ciborium::Value)>) -> Vec<u8> {
use ciborium::Value;
let map: Vec<(Value, Value)> = entries
.into_iter()
.map(|(k, v)| (Value::Integer(k.into()), v))
.collect();
let mut buf = Vec::new();
ciborium::ser::into_writer(&Value::Map(map), &mut buf).unwrap();
buf
}
#[test]
fn parse_cose_key_garbage_cbor_is_error() {
// 0xFF is a reserved CBOR major type: parse must fail, never panic.
let result = parse_cose_key(&[0xFF, 0xFF, 0xFF, 0xFF]);
assert!(matches!(result, Err(WebauthnError::VerificationFailed(_))));
}
#[test]
fn parse_cose_key_ec2_missing_crv() {
let buf = cose_key_from(vec![
(1, ciborium::Value::Integer(2.into())),
(2, ciborium::Value::Integer((-7).into())),
(-2, ciborium::Value::Bytes(vec![0xAA; 32])),
(-3, ciborium::Value::Bytes(vec![0xBB; 32])),
]);
assert!(matches!(
parse_cose_key(&buf),
Err(WebauthnError::VerificationFailed(_))
));
}
#[test]
fn parse_cose_key_ec2_wrong_curve_is_unsupported() {
let buf = cose_key_from(vec![
(1, ciborium::Value::Integer(2.into())),
(2, ciborium::Value::Integer((-7).into())),
(-1, ciborium::Value::Integer(3.into())), // P-384, not P-256
(-2, ciborium::Value::Bytes(vec![0xAA; 48])),
(-3, ciborium::Value::Bytes(vec![0xBB; 48])),
]);
assert!(matches!(
parse_cose_key(&buf),
Err(WebauthnError::UnsupportedAlgorithm(-7))
));
}
#[test]
fn parse_cose_key_ec2_missing_coordinates() {
let kty_alg = vec![
(1, ciborium::Value::Integer(2.into())),
(2, ciborium::Value::Integer((-7).into())),
(-1, ciborium::Value::Integer(1.into())),
];
let missing_x = cose_key_from(
[
kty_alg.clone(),
vec![(-3, ciborium::Value::Bytes(vec![0xBB; 32]))],
]
.concat(),
);
assert!(matches!(
parse_cose_key(&missing_x),
Err(WebauthnError::VerificationFailed(_))
));
let missing_y =
cose_key_from([kty_alg, vec![(-2, ciborium::Value::Bytes(vec![0xAA; 32]))]].concat());
assert!(matches!(
parse_cose_key(&missing_y),
Err(WebauthnError::VerificationFailed(_))
));
}
#[test]
fn parse_cose_key_rsa_missing_modulus_or_exponent() {
let missing_n = cose_key_from(vec![
(1, ciborium::Value::Integer(3.into())),
(2, ciborium::Value::Integer((-257).into())),
(-2, ciborium::Value::Bytes(vec![0x01, 0x00, 0x01])),
]);
assert!(matches!(
parse_cose_key(&missing_n),
Err(WebauthnError::VerificationFailed(_))
));
let missing_e = cose_key_from(vec![
(1, ciborium::Value::Integer(3.into())),
(2, ciborium::Value::Integer((-257).into())),
(-1, ciborium::Value::Bytes(vec![0xAA; 256])),
]);
assert!(matches!(
parse_cose_key(&missing_e),
Err(WebauthnError::VerificationFailed(_))
));
}
#[test]
fn parse_cose_key_unknown_kty_is_error() {
let buf = cose_key_from(vec![
(1, ciborium::Value::Integer(99.into())),
(2, ciborium::Value::Integer((-7).into())),
]);
assert!(matches!(
parse_cose_key(&buf),
Err(WebauthnError::VerificationFailed(_))
));
}
#[test]
fn cbor_map_entries_rejects_non_integer_keys() {
use ciborium::Value;
let map = Value::Map(vec![(
Value::Text("kty".to_string()),
Value::Integer(2.into()),
)]);
assert!(cbor_map_entries(&map).is_none());
}
#[test]
fn verify_rs256_with_ec_key_is_rejected() {
let key = CosePublicKey::Ec2 {
x: vec![0xAA; 32],
y: vec![0xBB; 32],
};
assert!(matches!(
verify_cose_signature(COSE_ALG_RS256, &key, b"data", &[0u8; 256]),
Err(WebauthnError::VerificationFailed(_))
));
}
#[test]
fn verify_cose_signature_unknown_alg_is_rejected() {
let key = CosePublicKey::Ec2 {
x: vec![0xAA; 32],
y: vec![0xBB; 32],
};
assert!(matches!(
verify_cose_signature(-47, &key, b"data", &[0u8; 64]),
Err(WebauthnError::UnsupportedAlgorithm(-47))
));
}
#[test]
fn alg_to_name_covers_known_and_unknown() {
assert_eq!(alg_to_name(COSE_ALG_ES256), "ES256");
assert_eq!(alg_to_name(COSE_ALG_RS256), "RS256");
assert_eq!(alg_to_name(0), "unknown");
}
/// RS256 end-to-end: a real 2048-bit RSA signature verifies through the
/// RS256 arm (PKCS#1 v1.5 + SHA-256), a tampered message fails closed.
#[test]
fn verify_rs256_real_signature_roundtrip() {
use ring::signature::{RsaKeyPair, RSA_PKCS1_SHA256};
let (n, e, pkcs8) = rsa_test_material();
let rsa = RsaKeyPair::from_pkcs8(&pkcs8).unwrap();
let modulus_len = rsa.public().modulus_len();
assert_eq!(modulus_len, 256);
// Sign with ring, verify through the COSE RS256 arm.
let rng = ring::rand::SystemRandom::new();
let message = b"webauthn-kit rs256 vector";
let mut signature = vec![0u8; modulus_len];
rsa.sign(&RSA_PKCS1_SHA256, &rng, message, &mut signature)
.unwrap();
let key = CosePublicKey::Rsa { n, e };
assert!(verify_cose_signature(COSE_ALG_RS256, &key, message, &signature).is_ok());
// One flipped message byte must fail closed.
let mut tampered = *message;
tampered[0] ^= 0x01;
assert!(matches!(
verify_cose_signature(COSE_ALG_RS256, &key, &tampered, &signature),
Err(WebauthnError::SignatureVerificationFailed)
));
}
/// DER long-form length encoding: a 128-byte modulus forces both the
/// standalone length encoder and the in-place header writer through
/// their `0x81` (single length byte) branches.
#[test]
fn der_long_form_length_encoding() {
let n = [0x77u8; 128];
let e = [0x01, 0x00, 0x01];
let der = RsaPublicKeyDer { n: &n, e: &e }.to_der().unwrap();
// RSAPublicKey: outer SEQ header uses the 0x81 long form.
assert_eq!(der[0], 0x30);
assert_eq!(der[1], 0x81);
assert_eq!(der[2] as usize + 3, der.len());
// The 128-byte INTEGER itself also uses the long form.
assert!(der.windows(3).any(|w| w == [0x02, 0x81, 0x80]));
}
}