docs: ml-dsa scheme everywhere

IMPLEMENTATION.md

@@ -67,18 +67,14 @@ The `program_client.nonce` column stores the **next usable nonce** — i.e. it i
 ## Cryptography
 
 ### Authentication
-- **Client protocol:** ed25519
+- **Client protocol:** ML-DSA
 
 ### User-Agent Authentication
 
 User-agent authentication supports multiple signature schemes because platform-provided "hardware-bound" keys do not expose a uniform algorithm across operating systems and hardware.
 
-- **Supported schemes:** RSA, Ed25519, ECDSA (secp256k1)
+- **Supported schemes:** ML-DSA
-- **Why:** the user agent authenticates with keys backed by platform facilities, and those facilities differ by platform
+- **Why:** Secure Enclave (MacOS) support them natively, on other platforms we could emulate while they roll-out
-- **Apple Silicon Secure Enclave / Secure Element:** ECDSA-only in practice
-- **Windows Hello / TPM 2.0:** currently RSA-backed in our integration
-
-This is why the user-agent auth protocol carries an explicit `KeyType`, while the SDK client protocol remains fixed to ed25519.
 
 ### Encryption at Rest
 - **Scheme:** Symmetric AEAD — currently **XChaCha20-Poly1305**

server/Cargo.lock

@@ -347,7 +347,7 @@ dependencies = [
  "ruint",
  "rustc-hash",
  "serde",
- "sha3",
+ "sha3 0.10.8",
 ]
 
 [[package]]
@@ -548,7 +548,7 @@ dependencies = [
  "proc-macro-error2",
  "proc-macro2",
  "quote",
- "sha3",
+ "sha3 0.10.8",
  "syn 2.0.117",
  "syn-solidity",
 ]
@@ -682,8 +682,8 @@ dependencies = [
  "alloy",
  "arbiter-proto",
  "async-trait",
- "ed25519-dalek",
  "http",
+ "ml-dsa",
  "rand 0.10.0",
  "rustls-webpki",
  "thiserror 2.0.18",
@@ -743,6 +743,7 @@ dependencies = [
  "k256",
  "kameo",
  "memsafe",
+ "ml-dsa",
  "mutants",
  "pem",
  "proptest",
@@ -751,14 +752,13 @@ dependencies = [
  "rand 0.10.0",
  "rcgen",
  "restructed",
- "rsa",
  "rstest",
  "rustls",
  "secrecy",
  "serde_with",
  "sha2 0.10.9",
  "smlang",
- "spki",
+ "spki 0.7.3",
  "strum 0.28.0",
  "subtle",
  "test-log",
@@ -1449,6 +1449,12 @@ dependencies = [
  "cc",
 ]
 
+[[package]]
+name = "cmov"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3f88a43d011fc4a6876cb7344703e297c71dda42494fee094d5f7c76bf13f746"
+
 [[package]]
 name = "console"
 version = "0.15.11"
@@ -1479,6 +1485,12 @@ version = "0.9.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c2459377285ad874054d797f3ccebf984978aa39129f6eafde5cdc8315b612f8"
 
+[[package]]
+name = "const-oid"
+version = "0.10.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a6ef517f0926dd24a1582492c791b6a4818a4d94e789a334894aa15b0d12f55c"
+
 [[package]]
 name = "const_format"
 version = "0.2.35"
@@ -1600,6 +1612,15 @@ dependencies = [
  "hybrid-array",
 ]
 
+[[package]]
+name = "ctutils"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7d5515a3834141de9eafb9717ad39eea8247b5674e6066c404e8c4b365d2a29e"
+dependencies = [
+ "cmov",
+]
+
 [[package]]
 name = "curve25519-dalek"
 version = "4.1.3"
@@ -1738,8 +1759,17 @@ version = "0.7.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e7c1832837b905bbfb5101e07cc24c8deddf52f93225eee6ead5f4d63d53ddcb"
 dependencies = [
- "const-oid",
+ "const-oid 0.9.6",
- "pem-rfc7468",
+ "zeroize",
+]
+
+[[package]]
+name = "der"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "71fd89660b2dc699704064e59e9dba0147b903e85319429e131620d022be411b"
+dependencies = [
+ "const-oid 0.10.2",
  "zeroize",
 ]
 
@@ -1882,7 +1912,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9ed9a281f7bc9b7576e61468ba615a66a5c8cfdff42420a70aa82701a3b1e292"
 dependencies = [
  "block-buffer 0.10.4",
- "const-oid",
+ "const-oid 0.9.6",
  "crypto-common 0.1.7",
  "subtle",
 ]
@@ -1946,13 +1976,13 @@ version = "0.16.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ee27f32b5c5292967d2d4a9d7f1e0b0aed2c15daded5a60300e4abb9d8020bca"
 dependencies = [
- "der",
+ "der 0.7.10",
  "digest 0.10.7",
  "elliptic-curve",
  "rfc6979",
  "serdect",
  "signature 2.2.0",
- "spki",
+ "spki 0.7.3",
 ]
 
 [[package]]
@@ -1961,7 +1991,6 @@ version = "3.0.0-rc.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c6e914c7c52decb085cea910552e24c63ac019e3ab8bf001ff736da9a9d9d890"
 dependencies = [
- "serde",
  "signature 3.0.0-rc.10",
 ]
 
@@ -1974,7 +2003,6 @@ dependencies = [
  "curve25519-dalek 5.0.0-pre.6",
  "ed25519",
  "rand_core 0.10.0",
- "serde",
  "sha2 0.11.0-rc.5",
  "subtle",
  "zeroize",
@@ -2013,7 +2041,7 @@ dependencies = [
  "ff",
  "generic-array",
  "group",
- "pkcs8",
+ "pkcs8 0.10.2",
  "rand_core 0.6.4",
  "sec1",
  "serdect",
@@ -2560,6 +2588,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8655f91cd07f2b9d0c24137bd650fe69617773435ee5ec83022377777ce65ef1"
 dependencies = [
  "typenum",
+ "zeroize",
 ]
 
 [[package]]
@@ -2957,6 +2986,16 @@ dependencies = [
  "cpufeatures 0.2.17",
 ]
 
+[[package]]
+name = "keccak"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9e24a010dd405bd7ed803e5253182815b41bf2e6a80cc3bfc066658e03a198aa"
+dependencies = [
+ "cfg-if",
+ "cpufeatures 0.3.0",
+]
+
 [[package]]
 name = "keccak-asm"
 version = "0.1.5"
@@ -2972,9 +3011,6 @@ name = "lazy_static"
 version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
-dependencies = [
- "spin",
-]
 
 [[package]]
 name = "leb128fmt"
@@ -3173,6 +3209,34 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "ml-dsa"
+version = "0.1.0-rc.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f5b2bb0ad6fa2b40396775bd56f51345171490fef993f46f91a876ecdbdaea55"
+dependencies = [
+ "const-oid 0.10.2",
+ "ctutils",
+ "hybrid-array",
+ "module-lattice",
+ "pkcs8 0.11.0-rc.11",
+ "rand_core 0.10.0",
+ "sha3 0.11.0",
+ "signature 3.0.0-rc.10",
+ "zeroize",
+]
+
+[[package]]
+name = "module-lattice"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "164eb3faeaecbd14b0b2a917c1b4d0c035097a9c559b0bed85c2cdd032bc8faa"
+dependencies = [
+ "hybrid-array",
+ "num-traits",
+ "zeroize",
+]
+
 [[package]]
 name = "multimap"
 version = "0.10.1"
@@ -3214,23 +3278,6 @@ dependencies = [
  "num-traits",
 ]
 
-[[package]]
-name = "num-bigint-dig"
-version = "0.8.6"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e661dda6640fad38e827a6d4a310ff4763082116fe217f279885c97f511bb0b7"
-dependencies = [
- "lazy_static",
- "libm",
- "num-integer",
- "num-iter",
- "num-traits",
- "rand 0.8.5",
- "serde",
- "smallvec",
- "zeroize",
-]
-
 [[package]]
 name = "num-conv"
 version = "0.2.0"
@@ -3246,17 +3293,6 @@ dependencies = [
  "num-traits",
 ]
 
-[[package]]
-name = "num-iter"
-version = "0.1.45"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1429034a0490724d0075ebb2bc9e875d6503c3cf69e235a8941aa757d83ef5bf"
-dependencies = [
- "autocfg",
- "num-integer",
- "num-traits",
-]
-
 [[package]]
 name = "num-traits"
 version = "0.2.19"
@@ -3426,15 +3462,6 @@ dependencies = [
  "serde_core",
 ]
 
-[[package]]
-name = "pem-rfc7468"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "88b39c9bfcfc231068454382784bb460aae594343fb030d46e9f50a645418412"
-dependencies = [
- "base64ct",
-]
-
 [[package]]
 name = "percent-encoding"
 version = "2.3.2"
@@ -3494,25 +3521,24 @@ version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8b870d8c151b6f2fb93e84a13146138f05d02ed11c7e7c54f8826aaaf7c9f184"
 
-[[package]]
-name = "pkcs1"
-version = "0.7.5"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c8ffb9f10fa047879315e6625af03c164b16962a5368d724ed16323b68ace47f"
-dependencies = [
- "der",
- "pkcs8",
- "spki",
-]
-
 [[package]]
 name = "pkcs8"
 version = "0.10.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f950b2377845cebe5cf8b5165cb3cc1a5e0fa5cfa3e1f7f55707d8fd82e0a7b7"
 dependencies = [
- "der",
+ "der 0.7.10",
- "spki",
+ "spki 0.7.3",
+]
+
+[[package]]
+name = "pkcs8"
+version = "0.11.0-rc.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "12922b6296c06eb741b02d7b5161e3aaa22864af38dfa025a1a3ba3f68c84577"
+dependencies = [
+ "der 0.8.0",
+ "spki 0.8.0",
 ]
 
 [[package]]
@@ -4152,28 +4178,6 @@ dependencies = [
  "rustc-hex",
 ]
 
-[[package]]
-name = "rsa"
-version = "0.9.10"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b8573f03f5883dcaebdfcf4725caa1ecb9c15b2ef50c43a07b816e06799bb12d"
-dependencies = [
- "const-oid",
- "digest 0.10.7",
- "num-bigint-dig",
- "num-integer",
- "num-traits",
- "pkcs1",
- "pkcs8",
- "rand_core 0.6.4",
- "serde",
- "sha2 0.10.9",
- "signature 2.2.0",
- "spki",
- "subtle",
- "zeroize",
-]
-
 [[package]]
 name = "rsqlite-vfs"
 version = "0.1.0"
@@ -4413,9 +4417,9 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d3e97a565f76233a6003f9f5c54be1d9c5bdfa3eccfb189469f11ec4901c47dc"
 dependencies = [
  "base16ct",
- "der",
+ "der 0.7.10",
  "generic-array",
- "pkcs8",
+ "pkcs8 0.10.2",
  "serdect",
  "subtle",
  "zeroize",
@@ -4609,7 +4613,17 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "75872d278a8f37ef87fa0ddbda7802605cb18344497949862c0d4dcb291eba60"
 dependencies = [
  "digest 0.10.7",
- "keccak",
+ "keccak 0.1.6",
+]
+
+[[package]]
+name = "sha3"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "be176f1a57ce4e3d31c1a166222d9768de5954f811601fb7ca06fc8203905ce1"
+dependencies = [
+ "digest 0.11.2",
+ "keccak 0.2.0",
 ]
 
 [[package]]
@@ -4662,6 +4676,10 @@ name = "signature"
 version = "3.0.0-rc.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7f1880df446116126965eeec169136b2e0251dba37c6223bcc819569550edea3"
+dependencies = [
+ "digest 0.11.2",
+ "rand_core 0.10.0",
+]
 
 [[package]]
 name = "simd-adler32"
@@ -4721,12 +4739,6 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
-[[package]]
-name = "spin"
-version = "0.9.8"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6980e8d7511241f8acf4aebddbb1ff938df5eebe98691418c4468d0b72a96a67"
-
 [[package]]
 name = "spki"
 version = "0.7.3"
@@ -4734,7 +4746,17 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d91ed6c858b01f942cd56b37a94b3e0a1798290327d1236e4d9cf4eaca44d29d"
 dependencies = [
  "base64ct",
- "der",
+ "der 0.7.10",
+]
+
+[[package]]
+name = "spki"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1d9efca8738c78ee9484207732f728b1ef517bbb1833d6fc0879ca898a522f6f"
+dependencies = [
+ "base64ct",
+ "der 0.8.0",
 ]
 
 [[package]]

server/Cargo.toml

@@ -20,7 +20,7 @@ tokio = { version = "1.50.0", features = ["full"] }
 ed25519-dalek = { version = "3.0.0-pre.6", features = ["rand_core"] }
 chrono = { version = "0.4.44", features = ["serde"] }
 rand = "0.10.0"
-rustls = { version = "0.23.37", features = ["aws-lc-rs"] }
+rustls = { version = "0.23.37", features = ["aws-lc-rs", "logging", "prefer-post-quantum", "std"], default-features = false }
 smlang = "0.8.0"
 thiserror = "2.0.18"
 async-trait = "0.1.89"
@@ -45,3 +45,4 @@ spki = "0.7"
 prost = "0.14.3"
 miette = { version = "7.6.0", features = ["fancy", "serde"] }
 mutants = "0.0.4"
+ml-dsa = { version = "0.1.0-rc.8", features = ["zeroize"] }

server/crates/arbiter-client/Cargo.toml

@@ -18,7 +18,7 @@ tonic.workspace = true
 tonic.features = ["tls-aws-lc"]
 tokio.workspace = true
 tokio-stream.workspace = true
-ed25519-dalek.workspace = true
+ml-dsa.workspace = true
 thiserror.workspace = true
 http = "1.4.0"
 rustls-webpki = { version = "0.103.10", features = ["aws-lc-rs"] }

server/crates/arbiter-client/src/auth.rs

@@ -1,5 +1,5 @@
 use arbiter_proto::{
-    ClientMetadata, format_challenge,
+    CLIENT_CONTEXT, ClientMetadata, format_challenge,
     proto::{
         client::{
             ClientRequest,
@@ -14,7 +14,7 @@ use arbiter_proto::{
         shared::ClientInfo as ProtoClientInfo,
     },
 };
-use ed25519_dalek::Signer as _;
+use ml_dsa::{MlDsa87, SigningKey, signature::Keypair as _};
 
 use crate::{
     storage::StorageError,
@@ -54,14 +54,14 @@ fn map_auth_result(code: i32) -> AuthError {
 async fn send_auth_challenge_request(
     transport: &mut ClientTransport,
     metadata: ClientMetadata,
-    key: &ed25519_dalek::SigningKey,
+    key: &SigningKey<MlDsa87>,
 ) -> std::result::Result<(), AuthError> {
     transport
         .send(ClientRequest {
             request_id: next_request_id(),
             payload: Some(ClientRequestPayload::Auth(proto_auth::Request {
                 payload: Some(AuthRequestPayload::ChallengeRequest(AuthChallengeRequest {
-                    pubkey: key.verifying_key().to_bytes().to_vec(),
+                    pubkey: key.verifying_key().encode().to_vec(),
                     client_info: Some(ProtoClientInfo {
                         name: metadata.name,
                         description: metadata.description,
@@ -95,11 +95,16 @@ async fn receive_auth_challenge(
 
 async fn send_auth_challenge_solution(
     transport: &mut ClientTransport,
-    key: &ed25519_dalek::SigningKey,
+    key: &SigningKey<MlDsa87>,
     challenge: AuthChallenge,
 ) -> std::result::Result<(), AuthError> {
     let challenge_payload = format_challenge(challenge.nonce, &challenge.pubkey);
-    let signature = key.sign(&challenge_payload).to_bytes().to_vec();
+    let signature = key
+        .signing_key()
+        .sign_deterministic(&challenge_payload, CLIENT_CONTEXT)
+        .map_err(|_| AuthError::UnexpectedAuthResponse)?
+        .encode()
+        .to_vec();
 
     transport
         .send(ClientRequest {
@@ -140,7 +145,7 @@ async fn receive_auth_confirmation(
 pub(crate) async fn authenticate(
     transport: &mut ClientTransport,
     metadata: ClientMetadata,
-    key: &ed25519_dalek::SigningKey,
+    key: &SigningKey<MlDsa87>,
 ) -> std::result::Result<(), AuthError> {
     send_auth_challenge_request(transport, metadata, key).await?;
     let challenge = receive_auth_challenge(transport).await?;

server/crates/arbiter-client/src/client.rs

@@ -1,6 +1,7 @@
 use arbiter_proto::{
     ClientMetadata, proto::arbiter_service_client::ArbiterServiceClient, url::ArbiterUrl,
 };
+use ml_dsa::{MlDsa87, SigningKey};
 use std::sync::Arc;
 use tokio::sync::{Mutex, mpsc};
 use tokio_stream::wrappers::ReceiverStream;
@@ -60,7 +61,7 @@ impl ArbiterClient {
     pub async fn connect_with_key(
         url: ArbiterUrl,
         metadata: ClientMetadata,
-        key: ed25519_dalek::SigningKey,
+        key: SigningKey<MlDsa87>,
     ) -> Result<Self, Error> {
         let anchor = webpki::anchor_from_trusted_cert(&url.ca_cert)?.to_owned();
         let tls = ClientTlsConfig::new().trust_anchor(anchor);

server/crates/arbiter-client/src/storage.rs

@@ -1,4 +1,5 @@
 use arbiter_proto::home_path;
+use ml_dsa::{KeyGen, MlDsa87, Seed, SigningKey};
 use std::path::{Path, PathBuf};
 
 #[derive(Debug, thiserror::Error)]
@@ -11,7 +12,7 @@ pub enum StorageError {
 }
 
 pub trait SigningKeyStorage {
-    fn load_or_create(&self) -> std::result::Result<ed25519_dalek::SigningKey, StorageError>;
+    fn load_or_create(&self) -> std::result::Result<SigningKey<MlDsa87>, StorageError>;
 }
 
 #[derive(Debug, Clone)]
@@ -20,7 +21,7 @@ pub struct FileSigningKeyStorage {
 }
 
 impl FileSigningKeyStorage {
-    pub const DEFAULT_FILE_NAME: &str = "sdk_client_ed25519.key";
+    pub const DEFAULT_FILE_NAME: &str = "sdk_client_ml_dsa.key";
 
     pub fn new(path: impl Into<PathBuf>) -> Self {
         Self { path: path.into() }
@@ -30,21 +31,20 @@ impl FileSigningKeyStorage {
         Ok(Self::new(home_path()?.join(Self::DEFAULT_FILE_NAME)))
     }
 
-    fn read_key(path: &Path) -> std::result::Result<ed25519_dalek::SigningKey, StorageError> {
+    fn read_key(path: &Path) -> std::result::Result<SigningKey<MlDsa87>, StorageError> {
         let bytes = std::fs::read(path)?;
-        let raw: [u8; 32] =
+        let raw: [u8; 32] = bytes
-            bytes
+            .try_into()
-                .try_into()
+            .map_err(|v: Vec<u8>| StorageError::InvalidKeyLength {
-                .map_err(|v: Vec<u8>| StorageError::InvalidKeyLength {
+                expected: 32,
-                    expected: 32,
+                actual: v.len(),
-                    actual: v.len(),
+            })?;
-                })?;
+        Ok(MlDsa87::from_seed(&Seed::from(raw)))
-        Ok(ed25519_dalek::SigningKey::from_bytes(&raw))
     }
 }
 
 impl SigningKeyStorage for FileSigningKeyStorage {
-    fn load_or_create(&self) -> std::result::Result<ed25519_dalek::SigningKey, StorageError> {
+    fn load_or_create(&self) -> std::result::Result<SigningKey<MlDsa87>, StorageError> {
         if let Some(parent) = self.path.parent() {
             std::fs::create_dir_all(parent)?;
         }
@@ -53,8 +53,8 @@ impl SigningKeyStorage for FileSigningKeyStorage {
             return Self::read_key(&self.path);
         }
 
-        let key = ed25519_dalek::SigningKey::generate(&mut rand::rng());
+        let key = MlDsa87::key_gen(&mut rand::rng());
-        let raw_key = key.to_bytes();
+        let raw_key = key.to_seed();
 
         // Use create_new to prevent accidental overwrite if another process creates the key first.
         match std::fs::OpenOptions::new()
@@ -103,7 +103,7 @@ mod tests {
             .load_or_create()
             .expect("second load_or_create should read same key");
 
-        assert_eq!(key_a.to_bytes(), key_b.to_bytes());
+        assert_eq!(key_a.to_seed(), key_b.to_seed());
         assert!(path.exists());
 
         std::fs::remove_file(path).expect("temp key file should be removable");

server/crates/arbiter-proto/src/lib.rs

@@ -63,6 +63,9 @@ pub mod proto {
     }
 }
 
+pub static CLIENT_CONTEXT: &[u8] = b"arbiter_client";
+pub static USERAGENT_CONTEXT: &[u8] = b"arbiter_user_agent";
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ClientMetadata {
     pub name: String,

server/crates/arbiter-server/Cargo.toml

@@ -16,8 +16,6 @@ diesel-async = { version = "0.8.0", features = [
     "sqlite",
     "tokio",
 ] }
-ed25519-dalek.workspace = true
-ed25519-dalek.features = ["serde"]
 arbiter-proto.path = "../arbiter-proto"
 tracing.workspace = true
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
@@ -40,16 +38,11 @@ chrono.workspace = true
 memsafe = "0.4.0"
 zeroize = { version = "1.8.2", features = ["std", "simd"] }
 kameo.workspace = true
-x25519-dalek.workspace = true
 chacha20poly1305 = { version = "0.10.1", features = ["std"] }
 argon2 = { version = "0.5.3", features = ["zeroize"] }
 restructed = "0.2.2"
 strum = { version = "0.28.0", features = ["derive"] }
 pem = "3.0.6"
-k256.workspace = true
-k256.features = ["serde"]
-rsa.workspace = true
-rsa.features = ["serde"]
 sha2.workspace = true
 hmac = "0.12"
 spki.workspace = true
@@ -61,6 +54,10 @@ anyhow = "1.0.102"
 serde_with = "3.18.0"
 mutants.workspace = true
 subtle = "2.6.1"
+ml-dsa.workspace = true
+ed25519-dalek.workspace = true
+x25519-dalek.workspace = true
+k256.workspace = true
 
 [dev-dependencies]
 insta = "1.46.3"

server/crates/arbiter-server/migrations/2026-02-14-171124-0000_init/up.sql

@@ -47,7 +47,7 @@ create table if not exists useragent_client (
     id integer not null primary key,
     nonce integer not null default(1), -- used for auth challenge
     public_key blob not null,
-    key_type integer not null default(1), -- 1=Ed25519, 2=ECDSA(secp256k1)
+    key_type integer not null default(1),
     created_at integer not null default(unixepoch ('now')),
     updated_at integer not null default(unixepoch ('now'))
 ) STRICT;

server/crates/arbiter-server/src/actors/client/auth.rs

@@ -1,5 +1,5 @@
 use arbiter_proto::{
-    ClientMetadata, format_challenge,
+    CLIENT_CONTEXT, ClientMetadata,
     transport::{Bi, expect_message},
 };
 use chrono::Utc;
@@ -8,7 +8,6 @@ use diesel::{
     dsl::insert_into, update,
 };
 use diesel_async::RunQueryDsl as _;
-use ed25519_dalek::{Signature, VerifyingKey};
 use kameo::{actor::ActorRef, error::SendError};
 use tracing::error;
 
@@ -18,6 +17,7 @@ use crate::{
         flow_coordinator::{self, RequestClientApproval},
         keyholder::KeyHolder,
     },
+    crypto::authn,
     crypto::integrity::{self, AttestationStatus},
     db::{
         self,
@@ -26,6 +26,8 @@ use crate::{
     },
 };
 
+
+
 #[derive(thiserror::Error, Debug, Clone, PartialEq, Eq)]
 pub enum Error {
     #[error("Database pool unavailable")]
@@ -62,17 +64,20 @@ pub enum ApproveError {
 #[derive(Debug, Clone)]
 pub enum Inbound {
     AuthChallengeRequest {
-        pubkey: VerifyingKey,
+        pubkey: authn::PublicKey,
         metadata: ClientMetadata,
     },
     AuthChallengeSolution {
-        signature: Signature,
+        signature: authn::Signature,
     },
 }
 
 #[derive(Debug, Clone)]
 pub enum Outbound {
-    AuthChallenge { pubkey: VerifyingKey, nonce: i32 },
+    AuthChallenge {
+        pubkey: authn::PublicKey,
+        nonce: i32,
+    },
     AuthSuccess,
 }
 
@@ -80,9 +85,9 @@ pub enum Outbound {
 /// Returns `None` if the pubkey is not registered.
 async fn get_current_nonce_and_id(
     db: &db::DatabasePool,
-    pubkey: &VerifyingKey,
+    pubkey: &authn::PublicKey,
 ) -> Result<Option<(i32, i32)>, Error> {
-    let pubkey_bytes = pubkey.as_bytes().to_vec();
+    let pubkey_bytes = pubkey.to_bytes();
     let mut conn = db.get().await.map_err(|e| {
         error!(error = ?e, "Database pool error");
         Error::DatabasePoolUnavailable
@@ -102,19 +107,17 @@ async fn get_current_nonce_and_id(
 async fn verify_integrity(
     db: &db::DatabasePool,
     keyholder: &ActorRef<KeyHolder>,
-    pubkey: &VerifyingKey,
+    pubkey: &authn::PublicKey,
 ) -> Result<(), Error> {
     let mut db_conn = db.get().await.map_err(|e| {
         error!(error = ?e, "Database pool error");
         Error::DatabasePoolUnavailable
     })?;
 
-    let (id, nonce) = get_current_nonce_and_id(db, pubkey)
+    let (id, nonce) = get_current_nonce_and_id(db, pubkey).await?.ok_or_else(|| {
-        .await?
+        error!("Client not found during integrity verification");
-        .ok_or_else(|| {
+        Error::DatabaseOperationFailed
-            error!("Client not found during integrity verification");
+    })?;
-            Error::DatabaseOperationFailed
-        })?;
 
     let attestation = integrity::verify_entity(
         &mut db_conn,
@@ -144,9 +147,9 @@ async fn verify_integrity(
 async fn create_nonce(
     db: &db::DatabasePool,
     keyholder: &ActorRef<KeyHolder>,
-    pubkey: &VerifyingKey,
+    pubkey: &authn::PublicKey,
 ) -> Result<i32, Error> {
-    let pubkey_bytes = pubkey.as_bytes().to_vec();
+    let pubkey_bytes = pubkey.to_bytes();
     let pubkey = pubkey.clone();
 
     let mut conn = db.get().await.map_err(|e| {
@@ -212,7 +215,7 @@ async fn approve_new_client(
 async fn insert_client(
     db: &db::DatabasePool,
     keyholder: &ActorRef<KeyHolder>,
-    pubkey: &VerifyingKey,
+    pubkey: &authn::PublicKey,
     metadata: &ClientMetadata,
 ) -> Result<i32, Error> {
     use crate::db::schema::{client_metadata, program_client};
@@ -242,7 +245,7 @@ async fn insert_client(
 
             let client_id = insert_into(program_client::table)
                 .values((
-                    program_client::public_key.eq(pubkey.as_bytes().to_vec()),
+                    program_client::public_key.eq(pubkey.to_bytes()),
                     program_client::metadata_id.eq(metadata_id),
                     program_client::nonce.eq(NONCE_START),
                 ))
@@ -345,14 +348,14 @@ async fn sync_client_metadata(
 
 async fn challenge_client<T>(
     transport: &mut T,
-    pubkey: VerifyingKey,
+    pubkey: authn::PublicKey,
     nonce: i32,
 ) -> Result<(), Error>
 where
     T: Bi<Inbound, Result<Outbound, Error>> + ?Sized,
 {
     transport
-        .send(Ok(Outbound::AuthChallenge { pubkey, nonce }))
+        .send(Ok(Outbound::AuthChallenge { pubkey: pubkey.clone(), nonce }))
         .await
         .map_err(|e| {
             error!(error = ?e, "Failed to send auth challenge");
@@ -369,12 +372,10 @@ where
         Error::Transport
     })?;
 
-    let formatted = format_challenge(nonce, pubkey.as_bytes());
+    if !pubkey.verify(nonce, CLIENT_CONTEXT, &signature) {
-
-    pubkey.verify_strict(&formatted, &signature).map_err(|_| {
         error!("Challenge solution verification failed");
-        Error::InvalidChallengeSolution
+        return Err(Error::InvalidChallengeSolution);
-    })?;
+    }
 
     Ok(())
 }
@@ -396,7 +397,7 @@ where
             approve_new_client(
                 &props.actors,
                 ClientProfile {
-                    pubkey,
+                    pubkey: pubkey.clone(),
                     metadata: metadata.clone(),
                 },
             )

server/crates/arbiter-server/src/actors/client/mod.rs

@@ -4,18 +4,19 @@ use tracing::{error, info};
 
 use crate::{
     actors::{GlobalActors, client::session::ClientSession},
+    crypto::authn,
     crypto::integrity::{Integrable, hashing::Hashable},
     db,
 };
 
 #[derive(Debug, Clone)]
 pub struct ClientProfile {
-    pub pubkey: ed25519_dalek::VerifyingKey,
+    pub pubkey: authn::PublicKey,
     pub metadata: ClientMetadata,
 }
 
 pub struct ClientCredentials {
-    pub pubkey: ed25519_dalek::VerifyingKey,
+    pub pubkey: authn::PublicKey,
     pub nonce: i32,
 }
 
@@ -25,7 +26,7 @@ impl Integrable for ClientCredentials {
 
 impl Hashable for ClientCredentials {
     fn hash<H: sha2::Digest>(&self, hasher: &mut H) {
-        hasher.update(self.pubkey.as_bytes());
+        hasher.update(self.pubkey.to_bytes());
         self.nonce.hash(hasher);
     }
 }
@@ -48,7 +49,12 @@ pub async fn connect_client<T>(mut props: ClientConnection, transport: &mut T)
 where
     T: Bi<auth::Inbound, Result<auth::Outbound, auth::Error>> + Send + ?Sized,
 {
-    match auth::authenticate(&mut props, transport).await {
+    let fut = auth::authenticate(&mut props, transport);
+    println!(
+        "authenticate future size: {}",
+        std::mem::size_of_val(&fut)
+    );
+    match fut.await {
         Ok(client_id) => {
             ClientSession::spawn(ClientSession::new(props, client_id));
             info!("Client authenticated, session started");

server/crates/arbiter-server/src/actors/user_agent/auth.rs

@@ -2,9 +2,10 @@ use arbiter_proto::transport::Bi;
 use tracing::error;
 
 use crate::actors::user_agent::{
-    AuthPublicKey, UserAgentConnection,
+    UserAgentConnection,
     auth::state::{AuthContext, AuthStateMachine},
 };
+use crate::crypto::authn;
 
 mod state;
 use state::*;
@@ -12,7 +13,7 @@ use state::*;
 #[derive(Debug, Clone)]
 pub enum Inbound {
     AuthChallengeRequest {
-        pubkey: AuthPublicKey,
+        pubkey: authn::PublicKey,
         bootstrap_token: Option<String>,
     },
     AuthChallengeSolution {
@@ -71,7 +72,7 @@ fn parse_auth_event(payload: Inbound) -> AuthEvents {
 pub async fn authenticate<T>(
     props: &mut UserAgentConnection,
     transport: T,
-) -> Result<AuthPublicKey, Error>
+) -> Result<authn::PublicKey, Error>
 where
     T: Bi<Inbound, Result<Outbound, Error>> + Send,
 {

server/crates/arbiter-server/src/actors/user_agent/auth/state.rs

@@ -1,7 +1,7 @@
-use arbiter_proto::transport::Bi;
+use arbiter_proto::{USERAGENT_CONTEXT, transport::Bi};
 use diesel::{ExpressionMethods as _, OptionalExtension as _, QueryDsl, update};
 use diesel_async::{AsyncConnection, RunQueryDsl};
-use kameo::{actor::ActorRef, error::SendError};
+use kameo::actor::ActorRef;
 use tracing::error;
 
 use super::Error;
@@ -9,24 +9,25 @@ use crate::{
     actors::{
         bootstrap::ConsumeToken,
         keyholder::KeyHolder,
-        user_agent::{AuthPublicKey, UserAgentConnection, UserAgentCredentials, auth::Outbound},
+        user_agent::{UserAgentConnection, UserAgentCredentials, auth::Outbound},
     },
-    crypto::integrity::{self, AttestationStatus},
+    crypto::authn,
+    crypto::integrity,
     db::{DatabasePool, schema::useragent_client},
 };
 
 pub struct ChallengeRequest {
-    pub pubkey: AuthPublicKey,
+    pub pubkey: authn::PublicKey,
 }
 
 pub struct BootstrapAuthRequest {
-    pub pubkey: AuthPublicKey,
+    pub pubkey: authn::PublicKey,
     pub token: String,
 }
 
 pub struct ChallengeContext {
     pub challenge_nonce: i32,
-    pub key: AuthPublicKey,
+    pub key: authn::PublicKey,
 }
 
 pub struct ChallengeSolution {
@@ -38,15 +39,15 @@ smlang::statemachine!(
     custom_error: true,
     transitions: {
         *Init + AuthRequest(ChallengeRequest) / async prepare_challenge = SentChallenge(ChallengeContext),
-        Init + BootstrapAuthRequest(BootstrapAuthRequest) / async verify_bootstrap_token = AuthOk(AuthPublicKey),
+        Init + BootstrapAuthRequest(BootstrapAuthRequest) / async verify_bootstrap_token = AuthOk(authn::PublicKey),
-        SentChallenge(ChallengeContext) + ReceivedSolution(ChallengeSolution) / async verify_solution = AuthOk(AuthPublicKey),
+        SentChallenge(ChallengeContext) + ReceivedSolution(ChallengeSolution) / async verify_solution = AuthOk(authn::PublicKey),
     }
 );
 
 /// Returns the current nonce, ready to use for the challenge nonce.
 async fn get_current_nonce_and_id(
     db: &DatabasePool,
-    key: &AuthPublicKey,
+    key: &authn::PublicKey,
 ) -> Result<(i32, i32), Error> {
     let mut db_conn = db.get().await.map_err(|e| {
         error!(error = ?e, "Database pool error");
@@ -56,8 +57,7 @@ async fn get_current_nonce_and_id(
         .exclusive_transaction(|conn| {
             Box::pin(async move {
                 useragent_client::table
-                    .filter(useragent_client::public_key.eq(key.to_stored_bytes()))
+                    .filter(useragent_client::public_key.eq(key.to_bytes()))
-                    .filter(useragent_client::key_type.eq(key.key_type()))
                     .select((useragent_client::id, useragent_client::nonce))
                     .first::<(i32, i32)>(conn)
                     .await
@@ -78,7 +78,7 @@ async fn get_current_nonce_and_id(
 async fn verify_integrity(
     db: &DatabasePool,
     keyholder: &ActorRef<KeyHolder>,
-    pubkey: &AuthPublicKey,
+    pubkey: &authn::PublicKey,
 ) -> Result<(), Error> {
     let mut db_conn = db.get().await.map_err(|e| {
         error!(error = ?e, "Database pool error");
@@ -87,7 +87,7 @@ async fn verify_integrity(
 
     let (id, nonce) = get_current_nonce_and_id(db, pubkey).await?;
 
-    let result = integrity::verify_entity(
+    let _result = integrity::verify_entity(
         &mut db_conn,
         keyholder,
         &UserAgentCredentials {
@@ -108,7 +108,7 @@ async fn verify_integrity(
 async fn create_nonce(
     db: &DatabasePool,
     keyholder: &ActorRef<KeyHolder>,
-    pubkey: &AuthPublicKey,
+    pubkey: &authn::PublicKey,
 ) -> Result<i32, Error> {
     let mut db_conn = db.get().await.map_err(|e| {
         error!(error = ?e, "Database pool error");
@@ -118,8 +118,7 @@ async fn create_nonce(
         .exclusive_transaction(|conn| {
             Box::pin(async move {
                 let (id, new_nonce): (i32, i32) = update(useragent_client::table)
-                    .filter(useragent_client::public_key.eq(pubkey.to_stored_bytes()))
+                    .filter(useragent_client::public_key.eq(pubkey.to_bytes()))
-                    .filter(useragent_client::key_type.eq(pubkey.key_type()))
                     .set(useragent_client::nonce.eq(useragent_client::nonce + 1))
                     .returning((useragent_client::id, useragent_client::nonce))
                     .get_result(conn)
@@ -154,10 +153,9 @@ async fn create_nonce(
 async fn register_key(
     db: &DatabasePool,
     keyholder: &ActorRef<KeyHolder>,
-    pubkey: &AuthPublicKey,
+    pubkey: &authn::PublicKey,
 ) -> Result<(), Error> {
-    let pubkey_bytes = pubkey.to_stored_bytes();
+    let pubkey_bytes = pubkey.to_bytes();
-    let key_type = pubkey.key_type();
     let mut conn = db.get().await.map_err(|e| {
         error!(error = ?e, "Database pool error");
         Error::internal("Database unavailable")
@@ -171,7 +169,6 @@ async fn register_key(
                 .values((
                     useragent_client::public_key.eq(pubkey_bytes),
                     useragent_client::nonce.eq(NONCE_START),
-                    useragent_client::key_type.eq(key_type),
                 ))
                 .returning(useragent_client::id)
                 .get_result(conn)
@@ -245,7 +242,7 @@ where
     async fn verify_bootstrap_token(
         &mut self,
         BootstrapAuthRequest { pubkey, token }: BootstrapAuthRequest,
-    ) -> Result<AuthPublicKey, Self::Error> {
+    ) -> Result<authn::PublicKey, Self::Error> {
         let token_ok: bool = self
             .conn
             .actors
@@ -293,35 +290,13 @@ where
             key,
         }: &ChallengeContext,
         ChallengeSolution { solution }: ChallengeSolution,
-    ) -> Result<AuthPublicKey, Self::Error> {
+    ) -> Result<authn::PublicKey, Self::Error> {
-        let formatted = arbiter_proto::format_challenge(*challenge_nonce, &key.to_stored_bytes());
+        let signature = authn::Signature::try_from(solution.as_slice()).map_err(|_| {
+            error!("Failed to decode signature in challenge solution");
+            Error::InvalidChallengeSolution
+        })?;
 
-        let valid = match key {
+        let valid = key.verify(*challenge_nonce, USERAGENT_CONTEXT, &signature);
-            AuthPublicKey::Ed25519(vk) => {
-                let sig = solution.as_slice().try_into().map_err(|_| {
-                    error!(?solution, "Invalid Ed25519 signature length");
-                    Error::InvalidChallengeSolution
-                })?;
-                vk.verify_strict(&formatted, &sig).is_ok()
-            }
-            AuthPublicKey::EcdsaSecp256k1(vk) => {
-                use k256::ecdsa::signature::Verifier as _;
-                let sig = k256::ecdsa::Signature::try_from(solution.as_slice()).map_err(|_| {
-                    error!(?solution, "Invalid ECDSA signature bytes");
-                    Error::InvalidChallengeSolution
-                })?;
-                vk.verify(&formatted, &sig).is_ok()
-            }
-            AuthPublicKey::Rsa(pk) => {
-                use rsa::signature::Verifier as _;
-                let verifying_key = rsa::pss::VerifyingKey::<sha2::Sha256>::new(pk.clone());
-                let sig = rsa::pss::Signature::try_from(solution.as_slice()).map_err(|_| {
-                    error!(?solution, "Invalid RSA signature bytes");
-                    Error::InvalidChallengeSolution
-                })?;
-                verifying_key.verify(&formatted, &sig).is_ok()
-            }
-        };
 
         match valid {
             true => {

server/crates/arbiter-server/src/actors/user_agent/mod.rs

@@ -1,22 +1,13 @@
 use crate::{
     actors::{GlobalActors, client::ClientProfile},
+    crypto::authn,
     crypto::integrity::Integrable,
-    db::{self, models::KeyType},
+    db,
 };
 
-/// Abstraction over Ed25519 / ECDSA-secp256k1 / RSA public keys used during the auth handshake.
-#[derive(Clone, Debug)]
-pub enum AuthPublicKey {
-    Ed25519(ed25519_dalek::VerifyingKey),
-    /// Compressed SEC1 public key; signature bytes are raw 64-byte (r||s).
-    EcdsaSecp256k1(k256::ecdsa::VerifyingKey),
-    /// RSA-2048+ public key (Windows Hello / KeyCredentialManager); signature bytes are PSS+SHA-256.
-    Rsa(rsa::RsaPublicKey),
-}
-
 #[derive(Debug)]
 pub struct UserAgentCredentials {
-    pub pubkey: AuthPublicKey,
+    pub pubkey: authn::PublicKey,
     pub nonce: i32,
 }
 
@@ -24,67 +15,11 @@ impl Integrable for UserAgentCredentials {
     const KIND: &'static str = "useragent_credentials";
 }
 
-impl AuthPublicKey {
-    /// Canonical bytes stored in DB and echoed back in the challenge.
-    /// Ed25519: raw 32 bytes. ECDSA: SEC1 compressed 33 bytes. RSA: DER-encoded SPKI.
-    pub fn to_stored_bytes(&self) -> Vec<u8> {
-        match self {
-            AuthPublicKey::Ed25519(k) => k.to_bytes().to_vec(),
-            // SEC1 compressed (33 bytes) is the natural compact format for secp256k1
-            AuthPublicKey::EcdsaSecp256k1(k) => k.to_encoded_point(true).as_bytes().to_vec(),
-            AuthPublicKey::Rsa(k) => {
-                use rsa::pkcs8::EncodePublicKey as _;
-                #[allow(clippy::expect_used)]
-                k.to_public_key_der()
-                    .expect("rsa SPKI encoding is infallible")
-                    .to_vec()
-            }
-        }
-    }
-
-    pub fn key_type(&self) -> KeyType {
-        match self {
-            AuthPublicKey::Ed25519(_) => KeyType::Ed25519,
-            AuthPublicKey::EcdsaSecp256k1(_) => KeyType::EcdsaSecp256k1,
-            AuthPublicKey::Rsa(_) => KeyType::Rsa,
-        }
-    }
-}
-
-impl TryFrom<(KeyType, Vec<u8>)> for AuthPublicKey {
-    type Error = &'static str;
-
-    fn try_from(value: (KeyType, Vec<u8>)) -> Result<Self, Self::Error> {
-        let (key_type, bytes) = value;
-        match key_type {
-            KeyType::Ed25519 => {
-                let bytes: [u8; 32] = bytes.try_into().map_err(|_| "invalid Ed25519 key length")?;
-                let key = ed25519_dalek::VerifyingKey::from_bytes(&bytes)
-                    .map_err(|_e| "invalid Ed25519 key")?;
-                Ok(AuthPublicKey::Ed25519(key))
-            }
-            KeyType::EcdsaSecp256k1 => {
-                let point =
-                    k256::EncodedPoint::from_bytes(&bytes).map_err(|_e| "invalid ECDSA key")?;
-                let key = k256::ecdsa::VerifyingKey::from_encoded_point(&point)
-                    .map_err(|_e| "invalid ECDSA key")?;
-                Ok(AuthPublicKey::EcdsaSecp256k1(key))
-            }
-            KeyType::Rsa => {
-                use rsa::pkcs8::DecodePublicKey as _;
-                let key = rsa::RsaPublicKey::from_public_key_der(&bytes)
-                    .map_err(|_e| "invalid RSA key")?;
-                Ok(AuthPublicKey::Rsa(key))
-            }
-        }
-    }
-}
-
 // Messages, sent by user agent to connection client without having a request
 #[derive(Debug)]
 pub enum OutOfBand {
     ClientConnectionRequest { profile: ClientProfile },
-    ClientConnectionCancel { pubkey: ed25519_dalek::VerifyingKey },
+    ClientConnectionCancel { pubkey: authn::PublicKey },
 }
 
 pub struct UserAgentConnection {
@@ -106,9 +41,9 @@ pub use session::UserAgentSession;
 
 use crate::crypto::integrity::hashing::Hashable;
 
-impl Hashable for AuthPublicKey {
+impl Hashable for authn::PublicKey {
     fn hash<H: sha2::Digest>(&self, hasher: &mut H) {
-        hasher.update(&self.to_stored_bytes());
+        hasher.update(self.to_bytes());
     }
 }
 

server/crates/arbiter-server/src/actors/user_agent/session.rs

@@ -2,7 +2,6 @@ use std::{borrow::Cow, collections::HashMap};
 
 use arbiter_proto::transport::Sender;
 use async_trait::async_trait;
-use ed25519_dalek::VerifyingKey;
 use kameo::{Actor, actor::ActorRef, messages};
 use thiserror::Error;
 use tracing::error;
@@ -12,6 +11,7 @@ use crate::actors::{
     flow_coordinator::{RegisterUserAgent, client_connect_approval::ClientApprovalController},
     user_agent::{OutOfBand, UserAgentConnection},
 };
+use crate::crypto::authn;
 
 mod state;
 use state::{DummyContext, UserAgentEvents, UserAgentStateMachine};
@@ -47,6 +47,7 @@ impl Error {
 }
 
 pub struct PendingClientApproval {
+    pubkey: authn::PublicKey,
     controller: ActorRef<ClientApprovalController>,
 }
 
@@ -55,7 +56,7 @@ pub struct UserAgentSession {
     state: UserAgentStateMachine<DummyContext>,
     sender: Box<dyn Sender<OutOfBand>>,
 
-    pending_client_approvals: HashMap<VerifyingKey, PendingClientApproval>,
+    pending_client_approvals: HashMap<Vec<u8>, PendingClientApproval>,
 }
 
 pub mod connection;
@@ -119,7 +120,13 @@ impl UserAgentSession {
         }
 
         self.pending_client_approvals
-            .insert(client.pubkey, PendingClientApproval { controller });
+            .insert(
+                client.pubkey.to_bytes(),
+                PendingClientApproval {
+                    pubkey: client.pubkey,
+                    controller,
+                },
+            );
     }
 }
 
@@ -158,14 +165,18 @@ impl Actor for UserAgentSession {
         let cancelled_pubkey = self
             .pending_client_approvals
             .iter()
-            .find_map(|(k, v)| (v.controller.id() == id).then_some(*k));
+            .find_map(|(k, v)| (v.controller.id() == id).then_some(k.clone()));
 
-        if let Some(pubkey) = cancelled_pubkey {
+        if let Some(pubkey_bytes) = cancelled_pubkey {
-            self.pending_client_approvals.remove(&pubkey);
+            let Some(approval) = self.pending_client_approvals.remove(&pubkey_bytes) else {
+                return Ok(std::ops::ControlFlow::Continue(()));
+            };
 
             if let Err(e) = self
                 .sender
-                .send(OutOfBand::ClientConnectionCancel { pubkey })
+                .send(OutOfBand::ClientConnectionCancel {
+                    pubkey: approval.pubkey,
+                })
                 .await
             {
                 error!(

server/crates/arbiter-server/src/actors/user_agent/session/connection.rs

@@ -13,6 +13,7 @@ use x25519_dalek::{EphemeralSecret, PublicKey};
 use crate::actors::flow_coordinator::client_connect_approval::ClientApprovalAnswer;
 use crate::actors::keyholder::KeyHolderState;
 use crate::actors::user_agent::session::Error;
+use crate::crypto::authn;
 use crate::db::models::{
     EvmWalletAccess, NewEvmWalletAccess, ProgramClient, ProgramClientMetadata,
 };
@@ -473,10 +474,13 @@ impl UserAgentSession {
     pub(crate) async fn handle_new_client_approve(
         &mut self,
         approved: bool,
-        pubkey: ed25519_dalek::VerifyingKey,
+        pubkey: authn::PublicKey,
         ctx: &mut Context<Self, Result<(), Error>>,
     ) -> Result<(), Error> {
-        let pending_approval = match self.pending_client_approvals.remove(&pubkey) {
+        let pending_approval = match self
+            .pending_client_approvals
+            .remove(&pubkey.to_bytes())
+        {
             Some(approval) => approval,
             None => {
                 error!("Received client connection response for unknown client");

server/crates/arbiter-server/src/crypto/authn/mod.rs

@@ -0,0 +1,3 @@
+pub mod v1;
+
+pub use v1::*;

server/crates/arbiter-server/src/crypto/authn/v1/mod.rs

@@ -0,0 +1,110 @@
+use ml_dsa::{
+    EncodedVerifyingKey, MlDsa87, Signature as MlDsaSignature, VerifyingKey as MlDsaVerifyingKey,
+};
+
+pub type KeyParams = MlDsa87;
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct PublicKey(Box<MlDsaVerifyingKey<KeyParams>>);
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct Signature(Box<MlDsaSignature<KeyParams>>);
+
+impl PublicKey {
+    pub fn to_bytes(&self) -> Vec<u8> {
+        self.0.encode().to_vec()
+    }
+
+    pub fn verify(&self, nonce: i32, context: &[u8], signature: &Signature) -> bool {
+        self.0.verify_with_context(&format_challenge(nonce, self), context, &signature.0)
+    }
+}
+
+impl Signature {
+    pub fn to_bytes(&self) -> Vec<u8> {
+        self.0.encode().to_vec()
+    }
+}
+
+impl From<MlDsaVerifyingKey<KeyParams>> for PublicKey {
+    fn from(value: MlDsaVerifyingKey<KeyParams>) -> Self {
+        Self(Box::new(value))
+    }
+}
+
+impl From<MlDsaSignature<KeyParams>> for Signature {
+    fn from(value: MlDsaSignature<KeyParams>) -> Self {
+        Self(Box::new(value))
+    }
+}
+
+impl TryFrom<&'_ [u8]> for PublicKey {
+    type Error = ();
+
+    fn try_from(value: &[u8]) -> Result<Self, Self::Error> {
+        let encoded = EncodedVerifyingKey::<KeyParams>::try_from(value).map_err(|_| ())?;
+        Ok(Self(Box::new(MlDsaVerifyingKey::decode(&encoded))))
+    }
+}
+
+impl TryFrom<&'_ [u8]> for Signature {
+    type Error = ();
+
+    fn try_from(value: &[u8]) -> Result<Self, Self::Error> {
+        MlDsaSignature::try_from(value)
+            .map(|sig| Self(Box::new(sig)))
+            .map_err(|_| ())
+    }
+}
+
+pub fn format_challenge(nonce: i32, pubkey: &PublicKey) -> Vec<u8> {
+    arbiter_proto::format_challenge(nonce, &pubkey.to_bytes())
+}
+
+#[cfg(test)]
+mod tests {
+    use ml_dsa::{KeyGen, MlDsa87, signature::Keypair as _};
+
+    use super::{PublicKey, Signature};
+
+    #[test]
+    fn public_key_round_trip_decodes() {
+        let key = MlDsa87::key_gen(&mut rand::rng());
+        let encoded = PublicKey::from(key.verifying_key()).to_bytes();
+
+        let decoded = PublicKey::try_from(encoded.as_slice()).expect("public key should decode");
+
+        assert_eq!(decoded, PublicKey::from(key.verifying_key()));
+    }
+
+    #[test]
+    fn signature_round_trip_decodes() {
+        let key = MlDsa87::key_gen(&mut rand::rng());
+        let challenge = b"challenge";
+        let signature = key
+            .signing_key()
+            .sign_deterministic(challenge, arbiter_proto::CLIENT_CONTEXT)
+            .expect("signature should be created");
+
+        let decoded = Signature::try_from(signature.encode().to_vec().as_slice()).expect("signature should decode");
+
+        assert_eq!(decoded, Signature::from(signature));
+    }
+
+    #[test]
+    fn challenge_verification_uses_context_and_canonical_key_bytes() {
+        let key = MlDsa87::key_gen(&mut rand::rng());
+        let public_key = PublicKey::from(key.verifying_key());
+        let nonce = 17;
+        let challenge =
+            arbiter_proto::format_challenge(nonce, &public_key.to_bytes());
+        let signature = key
+            .signing_key()
+            .sign_deterministic(&challenge, arbiter_proto::CLIENT_CONTEXT)
+            .expect("signature should be created")
+            .into();
+
+        assert!(public_key.verify(nonce, arbiter_proto::CLIENT_CONTEXT, &signature));
+        assert!(!public_key.verify(nonce, arbiter_proto::USERAGENT_CONTEXT, &signature));
+    }
+}

server/crates/arbiter-server/src/crypto/mod.rs

@@ -12,6 +12,7 @@ use rand::{
 
 use crate::safe_cell::{SafeCell, SafeCellHandle as _};
 
+pub mod authn;
 pub mod encryption;
 pub mod integrity;
 

server/crates/arbiter-server/src/db/models.rs

@@ -72,40 +72,6 @@ pub mod types {
             Ok(SqliteTimestamp(datetime))
         }
     }
-
-    /// Key algorithm stored in the `useragent_client.key_type` column.
-    /// Values must stay stable — they are persisted in the database.
-    #[derive(Debug, Clone, Copy, PartialEq, Eq, FromSqlRow, AsExpression, strum::FromRepr)]
-    #[diesel(sql_type = Integer)]
-    #[repr(i32)]
-    pub enum KeyType {
-        Ed25519 = 1,
-        EcdsaSecp256k1 = 2,
-        Rsa = 3,
-    }
-
-    impl ToSql<Integer, Sqlite> for KeyType {
-        fn to_sql<'b>(
-            &'b self,
-            out: &mut diesel::serialize::Output<'b, '_, Sqlite>,
-        ) -> diesel::serialize::Result {
-            out.set_value(*self as i32);
-            Ok(IsNull::No)
-        }
-    }
-
-    impl FromSql<Integer, Sqlite> for KeyType {
-        fn from_sql(
-            mut bytes: <Sqlite as diesel::backend::Backend>::RawValue<'_>,
-        ) -> diesel::deserialize::Result<Self> {
-            let Some(SqliteType::Long) = bytes.value_type() else {
-                return Err("Expected Integer for KeyType".into());
-            };
-            let discriminant = bytes.read_long();
-            KeyType::from_repr(discriminant as i32)
-                .ok_or_else(|| format!("Unknown KeyType discriminant: {discriminant}").into())
-        }
-    }
 }
 pub use types::*;
 
@@ -244,7 +210,6 @@ pub struct UseragentClient {
     pub public_key: Vec<u8>,
     pub created_at: SqliteTimestamp,
     pub updated_at: SqliteTimestamp,
-    pub key_type: KeyType,
 }
 
 #[derive(Models, Queryable, Debug, Insertable, Selectable)]

server/crates/arbiter-server/src/grpc/client/auth.rs

@@ -22,6 +22,7 @@ use tracing::warn;
 
 use crate::{
     actors::client::{self, ClientConnection, auth},
+    crypto::authn,
     grpc::request_tracker::RequestTracker,
 };
 
@@ -45,7 +46,7 @@ impl<'a> AuthTransportAdapter<'a> {
         match response {
             auth::Outbound::AuthChallenge { pubkey, nonce } => {
                 AuthResponsePayload::Challenge(ProtoAuthChallenge {
-                    pubkey: pubkey.to_bytes().to_vec(),
+                    pubkey: pubkey.to_bytes(),
                     nonce,
                 })
             }
@@ -160,11 +161,7 @@ impl Receiver<auth::Inbound> for AuthTransportAdapter<'_> {
                         .await;
                     return None;
                 };
-                let Ok(pubkey) = <[u8; 32]>::try_from(pubkey) else {
+                let Ok(pubkey) = authn::PublicKey::try_from(pubkey.as_slice()) else {
-                    let _ = self.send_auth_result(ProtoAuthResult::InvalidKey).await;
-                    return None;
-                };
-                let Ok(pubkey) = ed25519_dalek::VerifyingKey::from_bytes(&pubkey) else {
                     let _ = self.send_auth_result(ProtoAuthResult::InvalidKey).await;
                     return None;
                 };
@@ -174,7 +171,7 @@ impl Receiver<auth::Inbound> for AuthTransportAdapter<'_> {
                 })
             }
             AuthRequestPayload::ChallengeSolution(ProtoAuthChallengeSolution { signature }) => {
-                let Ok(signature) = ed25519_dalek::Signature::try_from(signature.as_slice()) else {
+                let Ok(signature) = authn::Signature::try_from(signature.as_slice()) else {
                     let _ = self
                         .send_auth_result(ProtoAuthResult::InvalidSignature)
                         .await;

server/crates/arbiter-server/src/grpc/user_agent/auth.rs

@@ -5,8 +5,7 @@ use arbiter_proto::{
             self as proto_auth, AuthChallenge as ProtoAuthChallenge,
             AuthChallengeRequest as ProtoAuthChallengeRequest,
             AuthChallengeSolution as ProtoAuthChallengeSolution, AuthResult as ProtoAuthResult,
-            KeyType as ProtoKeyType, request::Payload as AuthRequestPayload,
+            request::Payload as AuthRequestPayload, response::Payload as AuthResponsePayload,
-            response::Payload as AuthResponsePayload,
         },
         user_agent_request::Payload as UserAgentRequestPayload,
         user_agent_response::Payload as UserAgentResponsePayload,
@@ -18,8 +17,8 @@ use tonic::Status;
 use tracing::warn;
 
 use crate::{
-    actors::user_agent::{AuthPublicKey, UserAgentConnection, auth},
+    actors::user_agent::{UserAgentConnection, auth},
-    db::models::KeyType,
+    crypto::authn,
     grpc::request_tracker::RequestTracker,
 };
 
@@ -141,28 +140,9 @@ impl Receiver<auth::Inbound> for AuthTransportAdapter<'_> {
             AuthRequestPayload::ChallengeRequest(ProtoAuthChallengeRequest {
                 pubkey,
                 bootstrap_token,
-                key_type,
+                key_type: _,
             }) => {
-                let Ok(key_type) = ProtoKeyType::try_from(key_type) else {
+                let Ok(pubkey) = authn::PublicKey::try_from(pubkey.as_slice()) else {
-                    warn!(
-                        event = "received request with invalid key type",
-                        "grpc.useragent.auth_adapter"
-                    );
-                    return None;
-                };
-                let key_type = match key_type {
-                    ProtoKeyType::Ed25519 => KeyType::Ed25519,
-                    ProtoKeyType::EcdsaSecp256k1 => KeyType::EcdsaSecp256k1,
-                    ProtoKeyType::Rsa => KeyType::Rsa,
-                    ProtoKeyType::Unspecified => {
-                        warn!(
-                            event = "received request with unspecified key type",
-                            "grpc.useragent.auth_adapter"
-                        );
-                        return None;
-                    }
-                };
-                let Ok(pubkey) = AuthPublicKey::try_from((key_type, pubkey)) else {
                     warn!(
                         event = "received request with invalid public key",
                         "grpc.useragent.auth_adapter"
@@ -188,7 +168,7 @@ pub async fn start(
     conn: &mut UserAgentConnection,
     bi: &mut GrpcBi<UserAgentRequest, UserAgentResponse>,
     request_tracker: &mut RequestTracker,
-) -> Result<AuthPublicKey, auth::Error> {
+) -> Result<authn::PublicKey, auth::Error> {
     let transport = AuthTransportAdapter::new(bi, request_tracker);
     auth::authenticate(conn, transport).await
 }

server/crates/arbiter-server/src/grpc/user_agent/sdk_client.rs

@@ -27,6 +27,7 @@ use crate::{
             HandleRevokeEvmWalletAccess, HandleSdkClientList,
         },
     },
+    crypto::authn,
     db::models::NewEvmWalletAccess,
     grpc::Convert,
 };
@@ -41,7 +42,7 @@ pub(super) fn out_of_band_payload(oob: OutOfBand) -> UserAgentResponsePayload {
     match oob {
         OutOfBand::ClientConnectionRequest { profile } => wrap_sdk_client_response(
             SdkClientResponsePayload::ConnectionRequest(ProtoSdkClientConnectionRequest {
-                pubkey: profile.pubkey.to_bytes().to_vec(),
+                pubkey: profile.pubkey.to_bytes(),
                 info: Some(ProtoClientMetadata {
                     name: profile.metadata.name,
                     description: profile.metadata.description,
@@ -51,7 +52,7 @@ pub(super) fn out_of_band_payload(oob: OutOfBand) -> UserAgentResponsePayload {
         ),
         OutOfBand::ClientConnectionCancel { pubkey } => wrap_sdk_client_response(
             SdkClientResponsePayload::ConnectionCancel(ProtoSdkClientConnectionCancel {
-                pubkey: pubkey.to_bytes().to_vec(),
+                pubkey: pubkey.to_bytes(),
             }),
         ),
     }
@@ -89,10 +90,8 @@ async fn handle_connection_response(
     actor: &ActorRef<UserAgentSession>,
     resp: ProtoSdkClientConnectionResponse,
 ) -> Result<Option<UserAgentResponsePayload>, Status> {
-    let pubkey_bytes = <[u8; 32]>::try_from(resp.pubkey)
+    let pubkey = authn::PublicKey::try_from(resp.pubkey.as_slice())
-        .map_err(|_| Status::invalid_argument("Invalid Ed25519 public key length"))?;
+        .map_err(|_| Status::invalid_argument("Invalid ML-DSA public key"))?;
-    let pubkey = ed25519_dalek::VerifyingKey::from_bytes(&pubkey_bytes)
-        .map_err(|_| Status::invalid_argument("Invalid Ed25519 public key"))?;
 
     actor
         .ask(HandleNewClientApprove {
@@ -117,7 +116,7 @@ async fn handle_list(
                 .into_iter()
                 .map(|(client, metadata)| ProtoSdkClientEntry {
                     id: client.id,
-                    pubkey: client.public_key,
+                    pubkey: client.public_key.to_vec(),
                     info: Some(ProtoClientMetadata {
                         name: metadata.name,
                         description: metadata.description,

server/crates/arbiter-server/tests/client/auth.rs

@@ -6,13 +6,14 @@ use arbiter_server::{
         client::{ClientConnection, ClientCredentials, auth, connect_client},
         keyholder::Bootstrap,
     },
+    crypto::authn,
     crypto::integrity,
     db::{self, schema},
     safe_cell::{SafeCell, SafeCellHandle as _},
 };
 use diesel::{ExpressionMethods as _, NullableExpressionMethods as _, QueryDsl as _, insert_into};
 use diesel_async::RunQueryDsl;
-use ed25519_dalek::Signer as _;
+use ml_dsa::{KeyGen, MlDsa87, SigningKey, VerifyingKey, signature::Keypair as _};
 
 use super::common::ChannelTransport;
 
@@ -27,7 +28,7 @@ fn metadata(name: &str, description: Option<&str>, version: Option<&str>) -> Cli
 async fn insert_registered_client(
     db: &db::DatabasePool,
     actors: &GlobalActors,
-    pubkey: ed25519_dalek::VerifyingKey,
+    pubkey: VerifyingKey<MlDsa87>,
     metadata: &ClientMetadata,
 ) {
     use arbiter_server::db::schema::{client_metadata, program_client};
@@ -45,7 +46,7 @@ async fn insert_registered_client(
         .unwrap();
     let client_id: i32 = insert_into(program_client::table)
         .values((
-            program_client::public_key.eq(pubkey.to_bytes().to_vec()),
+            program_client::public_key.eq(pubkey.encode().to_vec()),
             program_client::metadata_id.eq(metadata_id),
         ))
         .returning(program_client::id)
@@ -56,18 +57,33 @@ async fn insert_registered_client(
     integrity::sign_entity(
         &mut conn,
         &actors.key_holder,
-        &ClientCredentials { pubkey, nonce: 1 },
+        &ClientCredentials {
+            pubkey: pubkey.into(),
+            nonce: 1,
+        },
         client_id,
     )
     .await
     .unwrap();
 }
 
+fn sign_client_challenge(
+    key: &SigningKey<MlDsa87>,
+    nonce: i32,
+    pubkey: &authn::PublicKey,
+) -> authn::Signature {
+    let challenge = arbiter_proto::format_challenge(nonce, &pubkey.to_bytes());
+    key.signing_key()
+        .sign_deterministic(&challenge, arbiter_proto::CLIENT_CONTEXT)
+        .unwrap()
+        .into()
+}
+
 async fn insert_bootstrap_sentinel_useragent(db: &db::DatabasePool) {
     let mut conn = db.get().await.unwrap();
-    let sentinel_key = ed25519_dalek::SigningKey::generate(&mut rand::rng())
+    let sentinel_key = MlDsa87::key_gen(&mut rand::rng())
         .verifying_key()
-        .to_bytes()
+        .encode()
         .to_vec();
 
     insert_into(schema::useragent_client::table)
@@ -107,11 +123,11 @@ pub async fn test_unregistered_pubkey_rejected() {
         connect_client(props, &mut server_transport).await;
     });
 
-    let new_key = ed25519_dalek::SigningKey::generate(&mut rand::rng());
+    let new_key = MlDsa87::key_gen(&mut rand::rng());
 
     test_transport
         .send(auth::Inbound::AuthChallengeRequest {
-            pubkey: new_key.verifying_key(),
+            pubkey: new_key.verifying_key().into(),
             metadata: metadata("client", Some("desc"), Some("1.0.0")),
         })
         .await
@@ -127,7 +143,7 @@ pub async fn test_challenge_auth() {
     let db = db::create_test_pool().await;
     let actors = spawn_test_actors(&db).await;
 
-    let new_key = ed25519_dalek::SigningKey::generate(&mut rand::rng());
+    let new_key = MlDsa87::key_gen(&mut rand::rng());
 
     insert_registered_client(
         &db,
@@ -147,7 +163,7 @@ pub async fn test_challenge_auth() {
     // Send challenge request
     test_transport
         .send(auth::Inbound::AuthChallengeRequest {
-            pubkey: new_key.verifying_key(),
+            pubkey: new_key.verifying_key().into(),
             metadata: metadata("client", Some("desc"), Some("1.0.0")),
         })
         .await
@@ -167,8 +183,7 @@ pub async fn test_challenge_auth() {
     };
 
     // Sign the challenge and send solution
-    let formatted_challenge = arbiter_proto::format_challenge(challenge.1, challenge.0.as_bytes());
+    let signature = sign_client_challenge(&new_key, challenge.1, &challenge.0);
-    let signature = new_key.sign(&formatted_challenge);
 
     test_transport
         .send(auth::Inbound::AuthChallengeSolution { signature })
@@ -194,7 +209,7 @@ pub async fn test_challenge_auth() {
 pub async fn test_metadata_unchanged_does_not_append_history() {
     let db = db::create_test_pool().await;
     let actors = spawn_test_actors(&db).await;
-    let new_key = ed25519_dalek::SigningKey::generate(&mut rand::rng());
+    let new_key = MlDsa87::key_gen(&mut rand::rng());
     let requested = metadata("client", Some("desc"), Some("1.0.0"));
 
     insert_registered_client(&db, &actors, new_key.verifying_key(), &requested).await;
@@ -209,7 +224,7 @@ pub async fn test_metadata_unchanged_does_not_append_history() {
 
     test_transport
         .send(auth::Inbound::AuthChallengeRequest {
-            pubkey: new_key.verifying_key(),
+            pubkey: new_key.verifying_key().into(),
             metadata: requested,
         })
         .await
@@ -220,7 +235,7 @@ pub async fn test_metadata_unchanged_does_not_append_history() {
         auth::Outbound::AuthChallenge { pubkey, nonce } => (pubkey, nonce),
         other => panic!("Expected AuthChallenge, got {other:?}"),
     };
-    let signature = new_key.sign(&arbiter_proto::format_challenge(nonce, pubkey.as_bytes()));
+    let signature = sign_client_challenge(&new_key, nonce, &pubkey);
     test_transport
         .send(auth::Inbound::AuthChallengeSolution { signature })
         .await
@@ -251,7 +266,7 @@ pub async fn test_metadata_unchanged_does_not_append_history() {
 pub async fn test_metadata_change_appends_history_and_repoints_binding() {
     let db = db::create_test_pool().await;
     let actors = spawn_test_actors(&db).await;
-    let new_key = ed25519_dalek::SigningKey::generate(&mut rand::rng());
+    let new_key = MlDsa87::key_gen(&mut rand::rng());
 
     insert_registered_client(
         &db,
@@ -271,7 +286,7 @@ pub async fn test_metadata_change_appends_history_and_repoints_binding() {
 
     test_transport
         .send(auth::Inbound::AuthChallengeRequest {
-            pubkey: new_key.verifying_key(),
+            pubkey: new_key.verifying_key().into(),
             metadata: metadata("client", Some("new"), Some("2.0.0")),
         })
         .await
@@ -282,7 +297,7 @@ pub async fn test_metadata_change_appends_history_and_repoints_binding() {
         auth::Outbound::AuthChallenge { pubkey, nonce } => (pubkey, nonce),
         other => panic!("Expected AuthChallenge, got {other:?}"),
     };
-    let signature = new_key.sign(&arbiter_proto::format_challenge(nonce, pubkey.as_bytes()));
+    let signature = sign_client_challenge(&new_key, nonce, &pubkey);
     test_transport
         .send(auth::Inbound::AuthChallengeSolution { signature })
         .await
@@ -339,7 +354,7 @@ pub async fn test_challenge_auth_rejects_integrity_tag_mismatch() {
     let db = db::create_test_pool().await;
     let actors = spawn_test_actors(&db).await;
 
-    let new_key = ed25519_dalek::SigningKey::generate(&mut rand::rng());
+    let new_key = MlDsa87::key_gen(&mut rand::rng());
     let requested = metadata("client", Some("desc"), Some("1.0.0"));
 
     {
@@ -357,7 +372,7 @@ pub async fn test_challenge_auth_rejects_integrity_tag_mismatch() {
             .unwrap();
         insert_into(program_client::table)
             .values((
-                program_client::public_key.eq(new_key.verifying_key().to_bytes().to_vec()),
+                program_client::public_key.eq(new_key.verifying_key().encode().to_vec()),
                 program_client::metadata_id.eq(metadata_id),
             ))
             .execute(&mut conn)
@@ -374,7 +389,7 @@ pub async fn test_challenge_auth_rejects_integrity_tag_mismatch() {
 
     test_transport
         .send(auth::Inbound::AuthChallengeRequest {
-            pubkey: new_key.verifying_key(),
+            pubkey: new_key.verifying_key().into(),
             metadata: requested,
         })
         .await

server/crates/arbiter-server/tests/user_agent/auth.rs

@@ -4,18 +4,31 @@ use arbiter_server::{
         GlobalActors,
         bootstrap::GetToken,
         keyholder::Bootstrap,
-        user_agent::{AuthPublicKey, UserAgentConnection, UserAgentCredentials, auth},
+        user_agent::{UserAgentConnection, UserAgentCredentials, auth},
     },
+    crypto::authn,
     crypto::integrity,
     db::{self, schema},
     safe_cell::{SafeCell, SafeCellHandle as _},
 };
 use diesel::{ExpressionMethods as _, QueryDsl, insert_into};
 use diesel_async::RunQueryDsl;
-use ed25519_dalek::Signer as _;
+use ml_dsa::{KeyGen, MlDsa87, SigningKey, signature::Keypair as _};
 
 use super::common::ChannelTransport;
 
+fn sign_useragent_challenge(
+    key: &SigningKey<MlDsa87>,
+    nonce: i32,
+    pubkey_bytes: &[u8],
+) -> authn::Signature {
+    let challenge = arbiter_proto::format_challenge(nonce, pubkey_bytes);
+    key.signing_key()
+        .sign_deterministic(&challenge, arbiter_proto::USERAGENT_CONTEXT)
+        .unwrap()
+        .into()
+}
+
 #[tokio::test]
 #[test_log::test]
 pub async fn test_bootstrap_token_auth() {
@@ -37,10 +50,10 @@ pub async fn test_bootstrap_token_auth() {
         auth::authenticate(&mut props, server_transport).await
     });
 
-    let new_key = ed25519_dalek::SigningKey::generate(&mut rand::rng());
+    let new_key = MlDsa87::key_gen(&mut rand::rng());
     test_transport
         .send(auth::Inbound::AuthChallengeRequest {
-            pubkey: AuthPublicKey::Ed25519(new_key.verifying_key()),
+            pubkey: new_key.verifying_key().into(),
             bootstrap_token: Some(token),
         })
         .await
@@ -63,7 +76,7 @@ pub async fn test_bootstrap_token_auth() {
         .first::<Vec<u8>>(&mut conn)
         .await
         .unwrap();
-    assert_eq!(stored_pubkey, new_key.verifying_key().to_bytes().to_vec());
+    assert_eq!(stored_pubkey, new_key.verifying_key().encode().to_vec());
 }
 
 #[tokio::test]
@@ -79,10 +92,10 @@ pub async fn test_bootstrap_invalid_token_auth() {
         auth::authenticate(&mut props, server_transport).await
     });
 
-    let new_key = ed25519_dalek::SigningKey::generate(&mut rand::rng());
+    let new_key = MlDsa87::key_gen(&mut rand::rng());
     test_transport
         .send(auth::Inbound::AuthChallengeRequest {
-            pubkey: AuthPublicKey::Ed25519(new_key.verifying_key()),
+            pubkey: new_key.verifying_key().into(),
             bootstrap_token: Some("invalid_token".to_string()),
         })
         .await
@@ -115,8 +128,8 @@ pub async fn test_challenge_auth() {
         .await
         .unwrap();
 
-    let new_key = ed25519_dalek::SigningKey::generate(&mut rand::rng());
+    let new_key = MlDsa87::key_gen(&mut rand::rng());
-    let pubkey_bytes = new_key.verifying_key().to_bytes().to_vec();
+    let pubkey_bytes = new_key.verifying_key().encode().to_vec();
 
     {
         let mut conn = db.get().await.unwrap();
@@ -133,7 +146,7 @@ pub async fn test_challenge_auth() {
             &mut conn,
             &actors.key_holder,
             &UserAgentCredentials {
-                pubkey: AuthPublicKey::Ed25519(new_key.verifying_key()),
+                pubkey: new_key.verifying_key().into(),
                 nonce: 1,
             },
             id,
@@ -151,7 +164,7 @@ pub async fn test_challenge_auth() {
 
     test_transport
         .send(auth::Inbound::AuthChallengeRequest {
-            pubkey: AuthPublicKey::Ed25519(new_key.verifying_key()),
+            pubkey: new_key.verifying_key().into(),
             bootstrap_token: None,
         })
         .await
@@ -169,12 +182,11 @@ pub async fn test_challenge_auth() {
         Err(err) => panic!("Expected Ok response, got Err({err:?})"),
     };
 
-    let formatted_challenge = arbiter_proto::format_challenge(challenge, &pubkey_bytes);
+    let signature = sign_useragent_challenge(&new_key, challenge, &pubkey_bytes);
-    let signature = new_key.sign(&formatted_challenge);
 
     test_transport
         .send(auth::Inbound::AuthChallengeSolution {
-            signature: signature.to_bytes().to_vec(),
+            signature: signature.to_bytes(),
         })
         .await
         .unwrap();
@@ -205,8 +217,8 @@ pub async fn test_challenge_auth_rejects_integrity_tag_mismatch_when_unsealed()
         .await
         .unwrap();
 
-    let new_key = ed25519_dalek::SigningKey::generate(&mut rand::rng());
+    let new_key = MlDsa87::key_gen(&mut rand::rng());
-    let pubkey_bytes = new_key.verifying_key().to_bytes().to_vec();
+    let pubkey_bytes = new_key.verifying_key().encode().to_vec();
 
     {
         let mut conn = db.get().await.unwrap();
@@ -229,7 +241,7 @@ pub async fn test_challenge_auth_rejects_integrity_tag_mismatch_when_unsealed()
 
     test_transport
         .send(auth::Inbound::AuthChallengeRequest {
-            pubkey: AuthPublicKey::Ed25519(new_key.verifying_key()),
+            pubkey: new_key.verifying_key().into(),
             bootstrap_token: None,
         })
         .await
@@ -254,8 +266,8 @@ pub async fn test_challenge_auth_rejects_invalid_signature() {
         .await
         .unwrap();
 
-    let new_key = ed25519_dalek::SigningKey::generate(&mut rand::rng());
+    let new_key = MlDsa87::key_gen(&mut rand::rng());
-    let pubkey_bytes = new_key.verifying_key().to_bytes().to_vec();
+    let pubkey_bytes = new_key.verifying_key().encode().to_vec();
 
     {
         let mut conn = db.get().await.unwrap();
@@ -272,7 +284,7 @@ pub async fn test_challenge_auth_rejects_invalid_signature() {
             &mut conn,
             &actors.key_holder,
             &UserAgentCredentials {
-                pubkey: AuthPublicKey::Ed25519(new_key.verifying_key()),
+                pubkey: new_key.verifying_key().into(),
                 nonce: 1,
             },
             id,
@@ -290,7 +302,7 @@ pub async fn test_challenge_auth_rejects_invalid_signature() {
 
     test_transport
         .send(auth::Inbound::AuthChallengeRequest {
-            pubkey: AuthPublicKey::Ed25519(new_key.verifying_key()),
+            pubkey: new_key.verifying_key().into(),
             bootstrap_token: None,
         })
         .await
@@ -308,12 +320,11 @@ pub async fn test_challenge_auth_rejects_invalid_signature() {
         Err(err) => panic!("Expected Ok response, got Err({err:?})"),
     };
 
-    let wrong_challenge = arbiter_proto::format_challenge(challenge + 1, &pubkey_bytes);
+    let signature = sign_useragent_challenge(&new_key, challenge + 1, &pubkey_bytes);
-    let signature = new_key.sign(&wrong_challenge);
 
     test_transport
         .send(auth::Inbound::AuthChallengeSolution {
-            signature: signature.to_bytes().to_vec(),
+            signature: signature.to_bytes(),
         })
         .await
         .unwrap();