Add support for custom JWS algorithms (#1410)

* Add support for custom JWS algorithms

This PR introduces a feature `custom_alg` to `identity_jose` (disabled
by default) that allows it to process JWS with custom `alg` values.

Switching on `custom_alg` makes quite a few changes to `JwsAlgorithm`:
- The type is no longer `Copy`
- `name()` takes only a reference and returns a `String` rather than
  `&'static str`
- The constant `ALL` is removed as it is no longer possible to enumerate
  all variants

* fmt

* Add comment

* Nightly fmt

* chore: add template for custom_alg file

* Split implementation of Display

---------

Co-authored-by: Yasir <yasir@shariff.dev>

Author: Frederik Rothenberger

identity_jose/Cargo.toml

@@ -34,3 +34,10 @@ test = true
 
 [lints]
 workspace = true
+
+[features]
+custom_alg = []
+
+[[test]]
+name = "custom_alg"
+required-features = ["custom_alg"]

identity_jose/src/jwk/key.rs

@@ -395,9 +395,9 @@ impl Jwk {
   // ===========================================================================
 
   /// Checks if the `alg` claim of the JWK is equal to `expected`.
-  pub fn check_alg(&self, expected: &str) -> Result<()> {
+  pub fn check_alg(&self, expected: impl AsRef<str>) -> Result<()> {
     match self.alg() {
-      Some(value) if value == expected => Ok(()),
+      Some(value) if value == expected.as_ref() => Ok(()),
       Some(_) => Err(Error::InvalidClaim("alg")),
       None => Ok(()),
     }

identity_jose/src/jws/algorithm.rs

@@ -6,12 +6,11 @@ use core::fmt::Formatter;
 use core::fmt::Result;
 use std::str::FromStr;
 
-use crate::error::Error;
-
 /// Supported algorithms for the JSON Web Signatures `alg` claim.
 ///
 /// [More Info](https://www.iana.org/assignments/jose/jose.xhtml#web-signature-encryption-algorithms)
-#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq, PartialOrd, Ord, serde::Deserialize, serde::Serialize)]
+#[derive(Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord, serde::Deserialize, serde::Serialize)]
+#[cfg_attr(not(feature = "custom_alg"), derive(Copy))]
 #[allow(non_camel_case_types)]
 pub enum JwsAlgorithm {
   /// HMAC using SHA-256
@@ -45,10 +44,19 @@ pub enum JwsAlgorithm {
   NONE,
   /// EdDSA signature algorithms
   EdDSA,
+  /// Custom algorithm
+  #[cfg(feature = "custom_alg")]
+  #[serde(untagged)]
+  Custom(String),
 }
 
 impl JwsAlgorithm {
   /// A slice of all supported [`JwsAlgorithm`]s.
+  ///
+  /// Not available when feature `custom_alg` is enabled
+  /// as it is not possible to enumerate all variants when
+  /// supporting arbitrary `alg` values.
+  #[cfg(not(feature = "custom_alg"))]
   pub const ALL: &'static [Self] = &[
     Self::HS256,
     Self::HS384,
@@ -68,6 +76,7 @@ impl JwsAlgorithm {
   ];
 
   /// Returns the JWS algorithm as a `str` slice.
+  #[cfg(not(feature = "custom_alg"))]
   pub const fn name(self) -> &'static str {
     match self {
       Self::HS256 => "HS256",
@@ -87,6 +96,29 @@ impl JwsAlgorithm {
       Self::EdDSA => "EdDSA",
     }
   }
+
+  /// Returns the JWS algorithm as a `str` slice.
+  #[cfg(feature = "custom_alg")]
+  pub fn name(&self) -> String {
+    match self {
+      Self::HS256 => "HS256".to_string(),
+      Self::HS384 => "HS384".to_string(),
+      Self::HS512 => "HS512".to_string(),
+      Self::RS256 => "RS256".to_string(),
+      Self::RS384 => "RS384".to_string(),
+      Self::RS512 => "RS512".to_string(),
+      Self::PS256 => "PS256".to_string(),
+      Self::PS384 => "PS384".to_string(),
+      Self::PS512 => "PS512".to_string(),
+      Self::ES256 => "ES256".to_string(),
+      Self::ES384 => "ES384".to_string(),
+      Self::ES512 => "ES512".to_string(),
+      Self::ES256K => "ES256K".to_string(),
+      Self::NONE => "none".to_string(),
+      Self::EdDSA => "EdDSA".to_string(),
+      Self::Custom(name) => name.clone(),
+    }
+  }
 }
 
 impl FromStr for JwsAlgorithm {
@@ -109,13 +141,24 @@ impl FromStr for JwsAlgorithm {
       "ES256K" => Ok(Self::ES256K),
       "none" => Ok(Self::NONE),
       "EdDSA" => Ok(Self::EdDSA),
-      _ => Err(Error::JwsAlgorithmParsingError),
+      #[cfg(feature = "custom_alg")]
+      value => Ok(Self::Custom(value.to_string())),
+      #[cfg(not(feature = "custom_alg"))]
+      _ => Err(crate::error::Error::JwsAlgorithmParsingError),
     }
   }
 }
 
+#[cfg(not(feature = "custom_alg"))]
 impl Display for JwsAlgorithm {
   fn fmt(&self, f: &mut Formatter<'_>) -> Result {
     f.write_str(self.name())
   }
 }
+
+#[cfg(feature = "custom_alg")]
+impl Display for JwsAlgorithm {
+  fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+    f.write_str(&(*self).name())
+  }
+}

identity_jose/src/jws/header.rs

@@ -67,7 +67,7 @@ impl JwsHeader {
 
   /// Returns the value for the algorithm claim (alg).
   pub fn alg(&self) -> Option<JwsAlgorithm> {
-    self.alg.as_ref().copied()
+    self.alg.as_ref().cloned()
   }
 
   /// Sets a value for the algorithm claim (alg).

identity_jose/tests/custom_alg.rs

@@ -0,0 +1,110 @@
+// Copyright 2020-2024 IOTA Stiftung
+// SPDX-License-Identifier: Apache-2.0
+
+use std::ops::Deref;
+use std::time::SystemTime;
+
+use crypto::signatures::ed25519::PublicKey;
+use crypto::signatures::ed25519::SecretKey;
+use crypto::signatures::ed25519::Signature;
+use identity_jose::jwk::EdCurve;
+use identity_jose::jwk::Jwk;
+use identity_jose::jwk::JwkParamsOkp;
+use identity_jose::jwk::JwkType;
+use identity_jose::jws::CompactJwsEncoder;
+use identity_jose::jws::Decoder;
+use identity_jose::jws::JwsAlgorithm;
+use identity_jose::jws::JwsHeader;
+use identity_jose::jws::JwsVerifierFn;
+use identity_jose::jws::SignatureVerificationError;
+use identity_jose::jws::SignatureVerificationErrorKind;
+use identity_jose::jws::VerificationInput;
+use identity_jose::jwt::JwtClaims;
+use identity_jose::jwu;
+use jsonprooftoken::encoding::base64url_decode;
+
+#[test]
+fn custom_alg_roundtrip() {
+  let secret_key = SecretKey::generate().unwrap();
+  let public_key = secret_key.public_key();
+
+  let mut header: JwsHeader = JwsHeader::new();
+  header.set_alg(JwsAlgorithm::Custom("test".to_string()));
+  let kid = "did:iota:0x123#signing-key";
+  header.set_kid(kid);
+
+  let mut claims: JwtClaims<serde_json::Value> = JwtClaims::new();
+  claims.set_iss("issuer");
+  claims.set_iat(
+    SystemTime::now()
+      .duration_since(SystemTime::UNIX_EPOCH)
+      .unwrap()
+      .as_secs() as i64,
+  );
+  claims.set_custom(serde_json::json!({"num": 42u64}));
+
+  let claims_bytes: Vec<u8> = serde_json::to_vec(&claims).unwrap();
+
+  let encoder: CompactJwsEncoder<'_> = CompactJwsEncoder::new(&claims_bytes, &header).unwrap();
+  let signing_input: &[u8] = encoder.signing_input();
+  let signature = secret_key.sign(signing_input).to_bytes();
+  let jws = encoder.into_jws(&signature);
+
+  let header = jws.split(".").next().unwrap();
+  let header_json = String::from_utf8(base64url_decode(header.as_bytes())).expect("failed to decode header");
+  assert_eq!(header_json, r#"{"kid":"did:iota:0x123#signing-key","alg":"test"}"#);
+
+  let verifier = JwsVerifierFn::from(|input: VerificationInput, key: &Jwk| {
+    if input.alg != JwsAlgorithm::Custom("test".to_string()) {
+      panic!("invalid algorithm");
+    }
+    verify(input, key)
+  });
+  let decoder = Decoder::new();
+  let mut public_key_jwk = Jwk::new(JwkType::Okp);
+  public_key_jwk.set_kid(kid);
+  public_key_jwk
+    .set_params(JwkParamsOkp {
+      crv: "Ed25519".into(),
+      x: jwu::encode_b64(public_key.as_slice()),
+      d: None,
+    })
+    .unwrap();
+
+  let token = decoder
+    .decode_compact_serialization(jws.as_bytes(), None)
+    .and_then(|decoded| decoded.verify(&verifier, &public_key_jwk))
+    .unwrap();
+
+  let recovered_claims: JwtClaims<serde_json::Value> = serde_json::from_slice(&token.claims).unwrap();
+
+  assert_eq!(token.protected.alg(), Some(JwsAlgorithm::Custom("test".to_string())));
+  assert_eq!(claims, recovered_claims);
+}
+
+fn verify(verification_input: VerificationInput, jwk: &Jwk) -> Result<(), SignatureVerificationError> {
+  let public_key = expand_public_jwk(jwk);
+
+  let signature_arr = <[u8; Signature::LENGTH]>::try_from(verification_input.decoded_signature.deref())
+    .map_err(|err| err.to_string())
+    .unwrap();
+
+  let signature = Signature::from_bytes(signature_arr);
+  if public_key.verify(&signature, &verification_input.signing_input) {
+    Ok(())
+  } else {
+    Err(SignatureVerificationErrorKind::InvalidSignature.into())
+  }
+}
+
+fn expand_public_jwk(jwk: &Jwk) -> PublicKey {
+  let params: &JwkParamsOkp = jwk.try_okp_params().unwrap();
+
+  if params.try_ed_curve().unwrap() != EdCurve::Ed25519 {
+    panic!("expected an ed25519 jwk");
+  }
+
+  let pk: [u8; PublicKey::LENGTH] = jwu::decode_b64(params.x.as_str()).unwrap().try_into().unwrap();
+
+  PublicKey::try_from(pk).unwrap()
+}

identity_storage/src/key_storage/memstore.rs

@@ -58,7 +58,7 @@ impl JwkStorage for JwkMemStore {
   async fn generate(&self, key_type: KeyType, alg: JwsAlgorithm) -> KeyStorageResult<JwkGenOutput> {
     let key_type: MemStoreKeyType = MemStoreKeyType::try_from(&key_type)?;
 
-    check_key_alg_compatibility(key_type, alg)?;
+    check_key_alg_compatibility(key_type, &alg)?;
 
     let (private_key, public_key) = match key_type {
       MemStoreKeyType::Ed25519 => {
@@ -102,7 +102,7 @@ impl JwkStorage for JwkMemStore {
       Some(alg) => {
         let alg: JwsAlgorithm = JwsAlgorithm::from_str(alg)
           .map_err(|err| KeyStorageError::new(KeyStorageErrorKind::UnsupportedSignatureAlgorithm).with_source(err))?;
-        check_key_alg_compatibility(key_type, alg)?;
+        check_key_alg_compatibility(key_type, &alg)?;
       }
       None => {
         return Err(
@@ -291,7 +291,7 @@ fn random_key_id() -> KeyId {
 }
 
 /// Check that the key type can be used with the algorithm.
-fn check_key_alg_compatibility(key_type: MemStoreKeyType, alg: JwsAlgorithm) -> KeyStorageResult<()> {
+fn check_key_alg_compatibility(key_type: MemStoreKeyType, alg: &JwsAlgorithm) -> KeyStorageResult<()> {
   match (key_type, alg) {
     (MemStoreKeyType::Ed25519, JwsAlgorithm::EdDSA) => Ok(()),
     (key_type, alg) => Err(

identity_stronghold/src/storage/stronghold_jwk_storage.rs

@@ -36,7 +36,7 @@ impl JwkStorage for StrongholdStorage {
 
     let client = get_client(&stronghold)?;
     let key_type = StrongholdKeyType::try_from(&key_type)?;
-    check_key_alg_compatibility(key_type, alg)?;
+    check_key_alg_compatibility(key_type, &alg)?;
 
     let keytype: ProceduresKeyType = match key_type {
       StrongholdKeyType::Ed25519 => ProceduresKeyType::Ed25519,
@@ -106,7 +106,7 @@ impl JwkStorage for StrongholdStorage {
       Some(alg) => {
         let alg: JwsAlgorithm = JwsAlgorithm::from_str(alg)
           .map_err(|err| KeyStorageError::new(KeyStorageErrorKind::UnsupportedSignatureAlgorithm).with_source(err))?;
-        check_key_alg_compatibility(key_type, alg)?;
+        check_key_alg_compatibility(key_type, &alg)?;
       }
       None => {
         return Err(

identity_stronghold/src/utils.rs

@@ -24,7 +24,7 @@ pub fn random_key_id() -> KeyId {
 }
 
 /// Check that the key type can be used with the algorithm.
-pub fn check_key_alg_compatibility(key_type: StrongholdKeyType, alg: JwsAlgorithm) -> KeyStorageResult<()> {
+pub fn check_key_alg_compatibility(key_type: StrongholdKeyType, alg: &JwsAlgorithm) -> KeyStorageResult<()> {
   match (key_type, alg) {
     (StrongholdKeyType::Ed25519, JwsAlgorithm::EdDSA) => Ok(()),
     (key_type, alg) => Err(