diff --git a/Cargo.lock b/Cargo.lock
index 5be1548..bb955e5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -81,9 +81,9 @@ dependencies = [
 
 [[package]]
 name = "autocfg"
-version = "1.0.1"
+version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
+checksum = "d468802bab17cbc0cc575e9b053f41e72aa36bfa6b7f55e3529ffa43161b97fa"
 
 [[package]]
 name = "base64"
@@ -272,7 +272,7 @@ version = "3.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a19c6cedffdc8c03a3346d723eb20bd85a13362bb96dc2ac000842c6381ec7bf"
 dependencies = [
- "nix",
+ "nix 0.23.1",
  "winapi",
 ]
 
@@ -722,6 +722,10 @@ name = "insecure_chat"
 version = "0.1.0"
 dependencies = [
  "mac_address",
+ "nix 0.25.0",
+ "ptth_diceware",
+ "thiserror",
+ "tokio",
 ]
 
 [[package]]
@@ -768,9 +772,9 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.122"
+version = "0.2.135"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ec647867e2bf0772e28c8bcde4f0d19a9216916e890543b5a03ed8ef27b8f259"
+checksum = "68783febc7782c6c5cb401fbda4de5a9898be1762314da0bb2c10ced61f18b0c"
 
 [[package]]
 name = "lock_api"
@@ -796,7 +800,7 @@ version = "1.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b238e3235c8382b7653c6408ed1b08dd379bdb9fdf990fb0bbae3db2cc0ae963"
 dependencies = [
- "nix",
+ "nix 0.23.1",
  "winapi",
 ]
 
@@ -852,25 +856,14 @@ checksum = "2a60c7ce501c71e03a9c9c0d35b861413ae925bd979cc7a4e30d060069aaac8d"
 
 [[package]]
 name = "mio"
-version = "0.8.2"
+version = "0.8.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "52da4364ffb0e4fe33a9841a98a3f3014fb964045ce4f7a45a398243c8d6b0c9"
+checksum = "57ee1c23c7c63b0c9250c339ffdc69255f110b298b901b9f6c82547b7b87caaf"
 dependencies = [
  "libc",
  "log",
- "miow",
- "ntapi",
  "wasi 0.11.0+wasi-snapshot-preview1",
- "winapi",
-]
-
-[[package]]
-name = "miow"
-version = "0.3.7"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b9f1c5b025cda876f66ef43a113f91ebc9f4ccef34843000e0adf6ebbab84e21"
-dependencies = [
- "winapi",
+ "windows-sys 0.36.1",
 ]
 
 [[package]]
@@ -905,12 +898,17 @@ dependencies = [
 ]
 
 [[package]]
-name = "ntapi"
-version = "0.3.6"
+name = "nix"
+version = "0.25.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3f6bb902e437b6d86e03cce10a7e2af662292c5dfef23b65899ea3ac9354ad44"
+checksum = "e322c04a9e3440c327fca7b6c8a63e6890a32fa2ad689db972425f07e0d22abb"
 dependencies = [
- "winapi",
+ "autocfg",
+ "bitflags",
+ "cfg-if",
+ "libc",
+ "memoffset",
+ "pin-utils",
 ]
 
 [[package]]
@@ -1013,7 +1011,7 @@ dependencies = [
  "libc",
  "redox_syscall",
  "smallvec",
- "windows-sys",
+ "windows-sys 0.34.0",
 ]
 
 [[package]]
@@ -1985,18 +1983,18 @@ dependencies = [
 
 [[package]]
 name = "thiserror"
-version = "1.0.29"
+version = "1.0.37"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "602eca064b2d83369e2b2f34b09c70b605402801927c65c11071ac911d299b88"
+checksum = "10deb33631e3c9018b9baf9dcbbc4f737320d2b576bac10f6aefa048fa407e3e"
 dependencies = [
  "thiserror-impl",
 ]
 
 [[package]]
 name = "thiserror-impl"
-version = "1.0.29"
+version = "1.0.37"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bad553cc2c78e8de258400763a647e80e6d1b31ee237275d756f6836d204494c"
+checksum = "982d17546b47146b28f7c22e3d08465f6b8903d0ea13c1660d9d84a6e7adcdbb"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -2040,16 +2038,16 @@ checksum = "cda74da7e1a664f795bb1f8a87ec406fb89a02522cf6e50620d016add6dbbf5c"
 
 [[package]]
 name = "tokio"
-version = "1.17.0"
+version = "1.21.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2af73ac49756f3f7c01172e34a23e5d0216f6c32333757c2c61feb2bbff5a5ee"
+checksum = "a9e03c497dc955702ba729190dc4aac6f2a0ce97f913e5b1b5912fc5039d9099"
 dependencies = [
+ "autocfg",
  "bytes",
  "libc",
  "memchr",
  "mio",
  "num_cpus",
- "once_cell",
  "parking_lot",
  "pin-project-lite",
  "signal-hook-registry",
@@ -2506,11 +2504,24 @@ version = "0.34.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5acdd78cb4ba54c0045ac14f62d8f94a03d10047904ae2a40afa1e99d8f70825"
 dependencies = [
- "windows_aarch64_msvc",
- "windows_i686_gnu",
- "windows_i686_msvc",
- "windows_x86_64_gnu",
- "windows_x86_64_msvc",
+ "windows_aarch64_msvc 0.34.0",
+ "windows_i686_gnu 0.34.0",
+ "windows_i686_msvc 0.34.0",
+ "windows_x86_64_gnu 0.34.0",
+ "windows_x86_64_msvc 0.34.0",
+]
+
+[[package]]
+name = "windows-sys"
+version = "0.36.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ea04155a16a59f9eab786fe12a4a450e75cdb175f9e0d80da1e17db09f55b8d2"
+dependencies = [
+ "windows_aarch64_msvc 0.36.1",
+ "windows_i686_gnu 0.36.1",
+ "windows_i686_msvc 0.36.1",
+ "windows_x86_64_gnu 0.36.1",
+ "windows_x86_64_msvc 0.36.1",
 ]
 
 [[package]]
@@ -2519,30 +2530,60 @@ version = "0.34.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "17cffbe740121affb56fad0fc0e421804adf0ae00891205213b5cecd30db881d"
 
+[[package]]
+name = "windows_aarch64_msvc"
+version = "0.36.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9bb8c3fd39ade2d67e9874ac4f3db21f0d710bee00fe7cab16949ec184eeaa47"
+
 [[package]]
 name = "windows_i686_gnu"
 version = "0.34.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2564fde759adb79129d9b4f54be42b32c89970c18ebf93124ca8870a498688ed"
 
+[[package]]
+name = "windows_i686_gnu"
+version = "0.36.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "180e6ccf01daf4c426b846dfc66db1fc518f074baa793aa7d9b9aaeffad6a3b6"
+
 [[package]]
 name = "windows_i686_msvc"
 version = "0.34.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9cd9d32ba70453522332c14d38814bceeb747d80b3958676007acadd7e166956"
 
+[[package]]
+name = "windows_i686_msvc"
+version = "0.36.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e2e7917148b2812d1eeafaeb22a97e4813dfa60a3f8f78ebe204bcc88f12f024"
+
 [[package]]
 name = "windows_x86_64_gnu"
 version = "0.34.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cfce6deae227ee8d356d19effc141a509cc503dfd1f850622ec4b0f84428e1f4"
 
+[[package]]
+name = "windows_x86_64_gnu"
+version = "0.36.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4dcd171b8776c41b97521e5da127a2d86ad280114807d0b2ab1e462bc764d9e1"
+
 [[package]]
 name = "windows_x86_64_msvc"
 version = "0.34.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d19538ccc21819d01deaf88d6a17eae6596a12e9aafdbb97916fb49896d89de9"
 
+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.36.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c811ca4a8c853ef420abd8592ba53ddbbac90410fab6903b3e79972a631f7680"
+
 [[package]]
 name = "winreg"
 version = "0.10.1"
diff --git a/crates/insecure_chat/Cargo.toml b/crates/insecure_chat/Cargo.toml
index 4ee1f0b..c3de3af 100644
--- a/crates/insecure_chat/Cargo.toml
+++ b/crates/insecure_chat/Cargo.toml
@@ -7,3 +7,7 @@ edition = "2021"
 
 [dependencies]
 mac_address = "1.1.4"
+nix = "0.25.0"
+ptth_diceware = { path = "../ptth_diceware" }
+thiserror = "1.0.37"
+tokio = { version = "1.21.2", features = ["net", "rt-multi-thread", "fs"] }
diff --git a/crates/insecure_chat/src/ip.rs b/crates/insecure_chat/src/ip.rs
new file mode 100644
index 0000000..44ab6ed
--- /dev/null
+++ b/crates/insecure_chat/src/ip.rs
@@ -0,0 +1,125 @@
+// IP address module
+// Copied from the `lookaround` project
+
+use std::{
+	net::Ipv4Addr,
+	process::Command,
+	str::FromStr,
+};
+
+#[derive (Debug, thiserror::Error)]
+pub enum Error {
+	#[error (transparent)]
+	Io (#[from] std::io::Error),
+	#[error (transparent)]
+	FromUtf8 (#[from] std::string::FromUtf8Error),
+	#[error ("Self-IP detection is not implemented on Mac OS")]
+	NotImplementedOnMac,
+}
+
+#[cfg(target_os = "linux")]
+pub fn get_ips () -> Result <Vec <Ipv4Addr>, Error> {
+	let output = linux::get_ip_addr_output ()?;
+	
+	Ok (linux::parse_ip_addr_output (&output))
+}
+
+#[cfg(target_os = "macos")]
+pub fn get_ips () -> Result <Vec <Ipv4Addr>, Error> {
+	Err (Error::NotImplementedOnMac)
+}
+
+#[cfg(target_os = "windows")]
+pub fn get_ips () -> Result <Vec <Ipv4Addr>, Error> {
+	let output = windows::get_ip_config_output ()?;
+	
+	Ok (windows::parse_ip_config_output (&output))
+}
+
+#[cfg(target_os = "linux")]
+pub mod linux {
+	use super::*;
+	
+	pub fn get_ip_addr_output () -> Result <String, Error> {
+		let output = Command::new ("ip")
+		.arg ("addr")
+		.output ()?;
+		let output = output.stdout.as_slice ();
+		let output = String::from_utf8 (output.to_vec ())?;
+		Ok (output)
+	}
+
+	pub fn parse_ip_addr_output (output: &str) -> Vec <Ipv4Addr> {
+		// I wrote this in FP style because I was bored.
+		
+		output.lines () 
+		.map (|l| l.trim_start ())
+		.filter_map (|l| l.strip_prefix ("inet "))
+		.filter_map (|l| l.find ('/').map (|x| &l [0..x]))
+		.filter_map (|l| Ipv4Addr::from_str (l).ok ())
+		.filter (|a| ! a.is_loopback ())
+		.collect ()
+	}
+}
+
+#[cfg(target_os = "windows")]
+pub mod windows {
+	use super::*;
+	
+	pub fn get_ip_config_output () -> Result <String, Error> {
+		let output = Command::new ("ipconfig")
+		.output ()?;
+		let output = output.stdout.as_slice ();
+		let output = String::from_utf8 (output.to_vec ())?;
+		Ok (output)
+	}
+
+	pub fn parse_ip_config_output (output: &str) -> Vec <Ipv4Addr> {
+		let mut addrs = vec! [];
+		
+		for line in output.lines () {
+			let line = line.trim_start ();
+			
+			// Maybe only works on English locales?
+			if ! line.starts_with ("IPv4 Address") {
+				continue;
+			}
+			let colon_pos = match line.find (':') {
+				None => continue,
+				Some (x) => x,
+			};
+			let line = &line [colon_pos + 2..];
+			
+			let addr = match Ipv4Addr::from_str (line) {
+				Err (_) => continue,
+				Ok (x) => x,
+			};
+			
+			addrs.push (addr);
+		}
+		
+		addrs
+	}
+
+	#[cfg (test)]
+	mod test {
+		use super::*;
+		
+		#[test]
+		fn test () {
+			for (input, expected) in [
+				(
+					r"
+	IPv4 Address .   .  .. . . . : 192.168.1.1
+	",
+					vec! [
+						Ipv4Addr::new (192, 168, 1, 1),
+					]
+				),
+			] {
+				let actual = parse_ip_config_output (input);
+				assert_eq! (actual, expected);
+			}
+		}
+	}
+}
diff --git a/crates/insecure_chat/src/main.rs b/crates/insecure_chat/src/main.rs
index abc0ac2..48c440e 100644
--- a/crates/insecure_chat/src/main.rs
+++ b/crates/insecure_chat/src/main.rs
@@ -1,18 +1,150 @@
 use std::{
 	net::{
-		IpAddr,
-		SocketAddr,
+		Ipv4Addr,
+		SocketAddrV4,
+		UdpSocket,
 	},
 };
 
-fn main () {
+mod ip;
+
+fn main () -> Result <(), Error>
+{
 	let mut args = std::env::args ();
 	let mut bail_unknown = true;
-	// let mut name = 
+	let mut last_unknown = None;
+	let mut name = ptth_diceware::passphrase ("_", 3);
+	let mut subcommand_count = 0;
+	let mut subcommand = None;
 	
-	for arg in args.next () {
-		
+	args.next ();
+	while let Some (arg) = args.next () {
+		if arg == "--ignore-unknown" {
+			bail_unknown = false;
+		}
+		if arg == "--name" {
+			name = args.next ().unwrap ().to_string ();
+		}
+		else if arg == "sender" {
+			subcommand = Some (Subcommand::Sender);
+			subcommand_count += 1;
+		}
+		else if arg == "spy" {
+			subcommand = Some (Subcommand::Spy);
+			subcommand_count += 1;
+		}
+		else {
+			last_unknown = Some (arg);
+		}
 	}
 	
-	unimplemented!();
+	if bail_unknown {
+		if let Some (last_unknown) = last_unknown {
+			eprintln! ("Unknown argument `{}`", last_unknown);
+			return Err (Error::Args);
+		}
+	}
+	
+	if subcommand_count >= 2 {
+		eprintln! ("Detected {} subcommands in arguments", subcommand_count);
+		return Err (Error::Args)
+	}
+	
+	let rt = tokio::runtime::Runtime::new ()?;
+	
+	let params = Params::default ();
+	
+	rt.block_on (async {
+		if let Some (cmd) = subcommand {
+			return match cmd {
+				Subcommand::Sender => sender (params).await,
+				Subcommand::Spy => spy (params),
+			};
+		}
+		
+		println! ("Name is `{}`", name);
+		
+		Ok::<_, Error> (())
+	})?;
+	
+	Ok (())
+}
+
+enum Subcommand {
+	Sender,
+	Spy,
+}
+
+struct Params {
+	multicast_group: (Ipv4Addr, u16),
+}
+
+impl Default for Params {
+	fn default () -> Self {
+		let multicast_group = (Ipv4Addr::new (225, 100, 99, 98), 9041);
+		
+		Self {
+			multicast_group,
+		}
+	}
+}
+
+async fn sender (params: Params) -> Result <(), Error>
+{
+	let socket = tokio::net::UdpSocket::bind (SocketAddrV4::new (Ipv4Addr::UNSPECIFIED, 0)).await?;
+	
+	let (multicast_addr, multicast_port) = params.multicast_group;
+	
+	socket.join_multicast_v4 (multicast_addr, Ipv4Addr::UNSPECIFIED)?;
+	eprintln! ("Multicast group is {:?}", params.multicast_group);
+	eprintln! ("Local addr is {}", socket.local_addr ()?);
+	
+	socket.send_to (&[], params.multicast_group).await?;
+	
+	Ok (())
+}
+
+fn spy (params: Params) -> Result <(), Error> 
+{
+	let (multicast_addr, multicast_port) = params.multicast_group;
+	
+	let socket = match UdpSocket::bind (SocketAddrV4::new (Ipv4Addr::UNSPECIFIED, multicast_port)) {
+		Ok (x) => x,
+		Err (e) => if e.kind () == std::io::ErrorKind::AddrInUse {
+			eprintln! ("Address in use. You can only run 1 instance of Insecure Chat at a time, even in spy mode.");
+			return Err (Error::AddrInUse);
+		}
+		else {
+			return Err (e.into ());
+		}
+	};
+	
+	for bind_addr in ip::get_ips ()? {
+		socket.join_multicast_v4 (&multicast_addr, &bind_addr)?;
+		// eprintln! ("Joined multicast with {}", bind_addr);
+	}
+	eprintln! ("Multicast addr is {}", multicast_addr);
+	eprintln! ("Local addr is {}", socket.local_addr ()?);
+	
+	loop {
+		let mut buf = vec! [0u8; 2048];
+		
+		eprintln! ("Listening for UDP packets...");
+		let (bytes_recved, remote_addr) = socket.recv_from (&mut buf)?;
+		buf.truncate (bytes_recved);
+		
+		println! ("Received {} bytes from {}", bytes_recved, remote_addr);
+	}
+}
+
+#[derive (Debug, thiserror::Error)]
+enum Error {
+	#[error ("Address in use")]
+	AddrInUse,
+	#[error ("CLI args")]
+	Args,
+	#[error (transparent)]
+	Io (#[from] std::io::Error),
+	#[error (transparent)]
+	Ip (#[from] ip::Error),
 }
diff --git a/crates/ptth_diceware/src/lib.rs b/crates/ptth_diceware/src/lib.rs
index 5ec217b..a72c310 100644
--- a/crates/ptth_diceware/src/lib.rs
+++ b/crates/ptth_diceware/src/lib.rs
@@ -1,15 +1,18 @@
 use rand::Rng;
 
 pub fn main () {
+	let passphrase = passphrase (" ", 8);
+	println! ("{}", passphrase);
+}
+
+pub fn passphrase (separator: &str, len: usize) -> String {
 	let diceware = Diceware::default ();
 	
-	let random_words: Vec <&str> = (0..8)
+	let random_words: Vec <&str> = (0..len)
 	.map (|_| diceware.random_word ())
 	.collect ();
 	
-	let passphrase = random_words.join (" ");
-	
-	println! ("{}", passphrase);
+	random_words.join (separator)
 }
 
 pub struct Diceware {