feat(app): allow hexadecimal HMAC key specification and redact keys from debug output

Cargo.lock

@@ -832,6 +832,7 @@ dependencies = [
  "crossterm",
  "ctrlc",
  "futures-core",
+ "hex",
  "irtt-client",
  "irtt-proto",
  "irtt-server",

crates/irtt-app/Cargo.toml

@@ -52,6 +52,7 @@ clap = { version = "4.6.7", features = ["derive", "env"] }
 clap-num = "=1.2.0"
 crossterm = { version = "0.29.0", features = ["event-stream"], optional = true }
 futures-core = { version = "0.3.34", default-features = false, optional = true }
+hex = "0.4.3"
 ctrlc = { version = "3.5.2", features = ["termination"] }
 irtt-client = { workspace = true, optional = true }
 irtt-proto = { workspace = true, optional = true }

crates/irtt-app/src/cmd/client/args.rs

@@ -16,7 +16,7 @@ pub struct ClientArgs {
         value_name = "TARGET",
         num_args = 0..,
         value_parser = parse_target,
-        long_help = "Server address/host, optionally prefixed with LABEL= and suffixed with @hmac=KEY. Repeat for multi-target mode.\n\nExamples:\n  irtt-client host-a:2112 host-b:2112\n  irtt-client eu=host-a:2112 us=host-b:2112\n  irtt-client ams=host-a:2112@hmac=secret public=host-b:2112@hmac=\n\nA target without @hmac= inherits --hmac. @hmac= explicitly disables it for that target."
+        long_help = "Server address/host, optionally prefixed with LABEL= and suffixed with @hmac=KEY. Repeat for multi-target mode. Keys use literal UTF-8 or lowercase 0x followed by hexadecimal bytes.\n\nExamples:\n  irtt-client host-a:2112 host-b:2112\n  irtt-client eu=host-a:2112 us=host-b:2112\n  irtt-client ams=host-a:2112@hmac=secret public=host-b:2112@hmac=\n\nA target without @hmac= inherits --hmac. @hmac= explicitly disables it for that target."
     )]
     pub targets: Vec<TargetArg>,
 

crates/irtt-app/src/cmd/server/args.rs

@@ -12,7 +12,7 @@ const DEFAULT_PORT: u16 = 2112;
 // Every policy option is optional. An omitted option leaves the corresponding
 // `ServerConfig` default in place rather than restating it here, so library and
 // CLI defaults cannot drift apart.
-#[derive(Debug, Clone, Parser)]
+#[derive(Clone, Parser)]
 #[command(
     name = "irtt-server",
     about = "Minimal IRTT-compatible UDP server",
@@ -28,13 +28,14 @@ pub struct ServerArgs {
     )]
     pub bind: Vec<SocketAddr>,
 
+    // Decode during configuration preparation so Clap cannot echo rejected keys.
     /// HMAC key; every request must then carry a valid MAC.
     #[arg(
         long,
         value_name = "KEY",
-        value_parser = parse_hmac_key,
         env = "IRTT_SERVER_HMAC",
-        long_help = "HMAC key, taken as the UTF-8 bytes of this argument.\n\nAuthentication is global: with a key configured, every request must carry a valid MAC and every reply is authenticated. Without one, authenticated requests are dropped. The key is visible in the process arguments, or in the environment as IRTT_SERVER_HMAC."
+        hide_env_values = true,
+        long_help = "HMAC key: literal UTF-8 or lowercase 0x followed by hexadecimal bytes (digits may use either case). Empty keys and invalid hex are rejected.\n\nAuthentication is global: with a key configured, every request must carry a valid MAC and every reply is authenticated. Without one, authenticated requests are dropped. The key is visible in the process arguments, or in the environment as IRTT_SERVER_HMAC."
     )]
     pub hmac: Option<String>,
 
@@ -126,6 +127,23 @@ pub struct ServerArgs {
     pub no_dscp: bool,
 }
 
+impl std::fmt::Debug for ServerArgs {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("ServerArgs")
+            .field("hmac", &self.hmac.as_ref().map(|_| "[REDACTED]"))
+            .field("bind", &self.bind)
+            .field("max_sessions", &self.max_sessions)
+            .field("max_packet_length", &self.max_packet_length)
+            .field("min_interval", &self.min_interval)
+            .field("burst", &self.burst)
+            .field("idle_timeout", &self.idle_timeout)
+            .field("max_duration", &self.max_duration)
+            .field("timestamp_allowance", &self.timestamp_allowance)
+            .field("no_dscp", &self.no_dscp)
+            .finish()
+    }
+}
+
 /// The command-line spelling of [`TimestampAllowance`].
 ///
 /// A CLI-local enum rather than a `clap` derive on the library type: `irtt-server`
@@ -166,11 +184,10 @@ impl ServerArgs {
     }
 
     /// Builds the server configuration this invocation asks for.
-    #[must_use]
+    pub fn server_config(&self) -> Result<ServerConfig, String> {
-    pub fn server_config(&self) -> ServerConfig {
         let mut config = ServerConfig::default();
         if let Some(key) = self.hmac.as_ref() {
-            config = config.with_hmac_key(key.as_bytes());
+            config = config.with_hmac_key(crate::shared::decode_hmac_key(key)?);
         }
         if let Some(value) = self.max_sessions {
             config = config.with_max_sessions(value);
@@ -198,19 +215,10 @@ impl ServerArgs {
         if self.no_dscp {
             config = config.with_dscp_allowed(false);
         }
-        config
+        Ok(config)
     }
 }
 
-/// Rejects an empty HMAC key so a blank shell expansion cannot silently
-/// enable authentication with predictable, empty key material.
-fn parse_hmac_key(input: &str) -> Result<String, String> {
-    if input.is_empty() {
-        return Err("HMAC key must not be empty".to_owned());
-    }
-    Ok(input.to_owned())
-}
-
 /// Parses a duration whose zero is meaningful server policy.
 fn parse_duration_allow_zero(input: &str) -> Result<Duration, String> {
     if input == "0" {

crates/irtt-app/src/cmd/server/run.rs

@@ -36,7 +36,7 @@ async fn serve(
     args: ServerArgs,
     shutdown_requested: &AtomicBool,
 ) -> Result<(), Box<dyn std::error::Error>> {
-    let config = args.server_config();
+    let config = args.server_config()?;
     let binds = args.resolve_binds();
     let is_implicit_default = args.bind.is_empty();
     let set = match ServerSet::bind(binds.clone(), config.clone()).await {

crates/irtt-app/src/cmd/tui/args.rs

@@ -18,7 +18,7 @@ pub struct TuiArgs {
         num_args = 1..,
         required = true,
         value_parser = parse_target,
-        long_help = "Server address/host, optionally prefixed with LABEL= and suffixed with @hmac=KEY. Repeat for multi-target mode.\n\nExplicit labels are used in the legend and status table. A target without @hmac= inherits --hmac; @hmac= disables it for that target.\n\nExamples:\n  irtt-tui host.example\n  irtt-tui eu=host.example\n  irtt-tui eu=host-a.example@hmac=secret us=host-b.example"
+        long_help = "Server address/host, optionally prefixed with LABEL= and suffixed with @hmac=KEY. Repeat for multi-target mode. Keys use literal UTF-8 or lowercase 0x followed by hexadecimal bytes.\n\nExplicit labels are used in the legend and status table. A target without @hmac= inherits --hmac; @hmac= disables it for that target.\n\nExamples:\n  irtt-tui host.example\n  irtt-tui eu=host.example\n  irtt-tui eu=host-a.example@hmac=secret us=host-b.example"
     )]
     pub targets: Vec<TargetArg>,
 

crates/irtt-app/src/shared/client/args.rs

@@ -26,8 +26,9 @@ pub struct CommonClientArgs {
     #[arg(long, default_value_t = 0, value_parser = parse_length)]
     pub length: u32,
 
-    /// HMAC key.
+    // Decode during configuration preparation so Clap cannot echo rejected keys.
-    #[arg(long, value_parser = parse_hmac_key)]
+    /// HMAC key: literal UTF-8 or lowercase 0x followed by hexadecimal bytes.
+    #[arg(long)]
     pub hmac: Option<String>,
 
     /// Clock mode to request.
@@ -267,13 +268,6 @@ pub fn parse_length(input: &str) -> Result<u32, String> {
     Ok(length)
 }
 
-pub fn parse_hmac_key(input: &str) -> Result<String, String> {
-    if input.is_empty() {
-        return Err("HMAC key must not be empty".to_owned());
-    }
-    Ok(input.to_owned())
-}
-
 pub fn parse_server_fill(input: &str) -> Result<String, String> {
     if input.is_empty() {
         return Err("server fill must not be empty".to_owned());

crates/irtt-app/src/shared/client/config.rs

@@ -21,8 +21,8 @@ impl CommonClientArgs {
     /// Build the shared client configuration template for a managed run.
     ///
     /// The config is endpoint-independent; managed targets own their addresses.
-    pub fn to_client_config(&self, duration: Duration) -> ClientConfig {
+    pub fn to_client_config(&self, duration: Duration) -> Result<ClientConfig, String> {
-        ClientConfig {
+        Ok(ClientConfig {
             address_family: self.address_family(),
             open: OpenPolicy {
                 negotiation: if self.loose {
@@ -45,9 +45,11 @@ impl CommonClientArgs {
             },
             auth: self
                 .hmac
-                .as_ref()
+                .as_deref()
+                .map(crate::shared::decode_hmac_key)
+                .transpose()?
                 .map_or(Authentication::Unauthenticated, |key| {
-                    Authentication::Hmac(HmacKey::new(key.as_bytes()))
+                    Authentication::Hmac(HmacKey::new(key))
                 }),
             socket: SocketConfig {
                 bind_addr: self.bind_addr,
@@ -61,7 +63,7 @@ impl CommonClientArgs {
                 ..SocketConfig::default()
             },
             ..ClientConfig::default()
-        }
+        })
     }
 }
 

crates/irtt-app/src/shared/client/prepare.rs

@@ -125,7 +125,7 @@ pub async fn prepare_managed_run(
         .await?;
     Ok(ManagedRunSetup {
         targets,
-        client: common.to_client_config(duration),
+        client: common.to_client_config(duration)?,
         pacing: selection.pacing.into(),
         stdin_controlled: selection.stdin_controlled,
         preparation,

crates/irtt-app/src/shared/client/targets.rs

@@ -88,12 +88,13 @@ impl From<GroupPacingArg> for ManagedPacing {
     }
 }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 enum TargetParseError {
     EmptyLabel,
     EmptyAddress,
     InvalidEscape,
     EmptyTarget,
+    InvalidHmac(String),
 }
 
 impl fmt::Display for TargetParseError {
@@ -103,6 +104,7 @@ impl fmt::Display for TargetParseError {
             Self::EmptyAddress => "target address must not be empty",
             Self::InvalidEscape => "invalid target escape sequence",
             Self::EmptyTarget => "target must not be empty",
+            Self::InvalidHmac(message) => message,
         };
         f.write_str(message)
     }
@@ -197,7 +199,10 @@ fn parse_target_syntax(
             let auth = if value.is_empty() {
                 TargetAuth::Override(Authentication::Unauthenticated)
             } else {
-                TargetAuth::Override(Authentication::Hmac(HmacKey::new(value.into_bytes())))
+                TargetAuth::Override(Authentication::Hmac(HmacKey::new(
+                    crate::shared::decode_hmac_key(&value)
+                        .map_err(TargetParseError::InvalidHmac)?,
+                )))
             };
             (&input[..index], auth)
         }

crates/irtt-app/src/shared/hmac.rs

@@ -0,0 +1,14 @@
+/// Decode CLI key syntax without ever including key material in diagnostics.
+pub(crate) fn decode_hmac_key(input: &str) -> Result<Vec<u8>, String> {
+    let key = match input.strip_prefix("0x") {
+        Some(hex) => hex::decode(hex).map_err(|_| {
+            "HMAC hexadecimal key must contain an even number of valid hexadecimal digits"
+                .to_owned()
+        })?,
+        None => input.as_bytes().to_vec(),
+    };
+    if key.is_empty() {
+        return Err("HMAC key must not be empty".to_owned());
+    }
+    Ok(key)
+}

crates/irtt-app/src/shared/mod.rs

@@ -1,2 +1,7 @@
 #[cfg(any(feature = "client", feature = "tui"))]
 pub mod client;
+
+#[cfg(any(feature = "client", feature = "tui", feature = "server"))]
+mod hmac;
+#[cfg(any(feature = "client", feature = "tui", feature = "server"))]
+pub(crate) use hmac::decode_hmac_key;

docs/irtt-client.md

@@ -37,12 +37,13 @@ overrides it for that target, and `@hmac=` explicitly disables HMAC for that
 target. The modifier uses `@`, not a shell command separator; quote an argument
 if its key needs shell quoting.
 
+Global `--hmac KEY` and per-target `@hmac=KEY` accept plain-text keys or hexadecimal keys prefixed with `0x`. For example, `secret` and `0x736563726574` are equivalent.
+
 Target syntax supports these backslash escapes in labels, addresses, and HMAC
 values: `\\` for a literal backslash, `\@` for a literal `@`, `\=` for a
 literal `=`, and `\;` for a literal semicolon. Escaping `@` is necessary in a
 label or address when it would otherwise begin `@hmac=`; escaping the first
-`=` is how an unlabeled target or a label can contain that character. An `=` in
+`=` is how an unlabeled target or a label can contain that character. An `=` in an HMAC value does not need escaping. Positional
-an HMAC value, including Base64 padding, does not need escaping. Positional
 target arguments may contain a raw comma; stdin target sets have the additional
 `\,` escape described below.
 

docs/irtt-server.md

@@ -74,8 +74,9 @@ IPv6 listener.
 
 ### `--hmac KEY`
 
-HMAC key, taken as the UTF-8 bytes of this argument. With a key configured,
+Accepts a plain-text key or a hexadecimal key prefixed with `0x`. For example, `secret` and `0x736563726574` are equivalent. The `IRTT_SERVER_HMAC` environment variable uses the same syntax.
-every request must carry a valid MAC and every reply is authenticated;
+
+With a key configured, every request must carry a valid MAC and every reply is authenticated;
 without one, authenticated requests are dropped. The key is visible in the
 process arguments.