diff --git a/crates/rrg/src/action/execute_signed_command.rs b/crates/rrg/src/action/execute_signed_command.rs
index f6e1b7c7..0a59d947 100644
--- a/crates/rrg/src/action/execute_signed_command.rs
+++ b/crates/rrg/src/action/execute_signed_command.rs
@@ -3,10 +3,14 @@
 // Use of this source code is governed by an MIT-style license that can be found
 // in the LICENSE file or at https://opensource.org/licenses/MIT.
 
-use std::process::ExitStatus;
+use std::{collections::HashMap, env, io::{Read, Write}, process::{Command, ExitStatus}};
 
 use protobuf::Message;
 
+// TODO(s-westphal): Check and update max size.
+const MAX_OUTPUT_SIZE: usize = 1024;
+const COMMAND_EXECUTION_CHECK_INTERVAL: std::time::Duration = std::time::Duration::from_secs(1);
+
 /// Arguments of the `execute_signed_command` action.
 pub struct Args {
     raw_command: Vec<u8>,
@@ -42,7 +46,100 @@ pub fn handle<S>(session: &mut S, mut args: Args) -> crate::session::Result<()>
 where
     S: crate::session::Session,
 {
-    // TODO(s-westphal): Add implementation.
+    match session.args().command_verification_key {
+        Some(key) => key.verify_strict(&args.raw_command, &args.ed25519_signature)
+            .map_err(crate::session::Error::action)?,
+        None => panic!("missing verification key for signed command"),
+    };
+
+    let command_path = &std::path::PathBuf::try_from(args.command.take_path())
+        .map_err(crate::session::Error::action)?;
+
+    // let filtered_env : HashMap<String, String> =
+    //     env::vars().filter(|&(ref k, _)|
+    //         k == "TERM" || k == "TZ" || k == "LANG" || k == "PATH" || k == "LD_LIBRARY_PATH"
+    //     ).collect();
+
+    let mut command_process = Command::new(command_path)
+        .stdin(std::process::Stdio::piped())
+        .args(args.command.take_args())
+        // TODO(@s-westphal): Clearing the env removes the PATH, which is not included
+        // in the filtered_env in windows. But the path is required for calling
+        // `cmd /C findstr`` etc.
+        // .env_clear() 
+        // .envs(filtered_env)
+        .envs(args.command.take_env())
+        .stdout(std::process::Stdio::piped())
+        .stderr(std::process::Stdio::piped())
+        .spawn()
+        .map_err(crate::session::Error::action)?;
+
+    let command_start_time = std::time::SystemTime::now();
+
+    let mut command_stdin = match command_process.stdin.take() {
+        Some(command_stdin) => command_stdin,
+        None => panic!("command stdin pipe should not be None")
+    };
+    let handle = std::thread::spawn(move || {
+        match args.stdin {
+            Stdin::SIGNED(signed) => command_stdin.write(&signed[..]).expect("Failed to write to stdin"),
+            Stdin::UNSIGNED(unsigned) => command_stdin.write(&unsigned[..]).expect("Failed to write to stdin"),
+            Stdin::NONE => 0,
+        };
+    });
+
+    // TODO(s-westphal): join returns a `Box<dyn std::any::Any + Send>`
+    // error which cannot be passed to crate:session:Error::action.
+    let _ = handle.join().unwrap();
+
+    while std::time::SystemTime::now().duration_since(command_start_time).unwrap() < args.timeout {
+        match command_process.try_wait() {
+            Ok(None) => {
+                log::debug!("command not completed, waiting {:?}", COMMAND_EXECUTION_CHECK_INTERVAL);
+                std::thread::sleep(COMMAND_EXECUTION_CHECK_INTERVAL);
+            }
+            _ => break,
+        }
+    }
+    // Either the process has exited, then kill doesn't do anything,
+    // or we kill the process.
+    command_process.kill().map_err(crate::session::Error::action)?;
+
+    let exit_status = command_process.wait()
+        .map_err(crate::session::Error::action)?;
+
+    let mut stdout = Vec::<u8>::new();
+    let length_stdout = match command_process.stdout.take() {
+        Some(mut process_stdout) => {
+            process_stdout.read_to_end(&mut stdout).map_err(crate::session::Error::action)?
+        }
+        None => 0,
+    };
+    let truncated_stdout = length_stdout > MAX_OUTPUT_SIZE;
+    if truncated_stdout {
+        stdout.truncate(MAX_OUTPUT_SIZE);
+    };
+
+    let mut stderr = Vec::<u8>::new();
+    let length_stderr = match command_process.stderr.take() {
+        Some(mut process_stderr) => {
+            process_stderr.read_to_end(&mut stderr).map_err(crate::session::Error::action)?
+        }
+        None => 0,
+    };
+    let truncated_stderr = length_stderr > MAX_OUTPUT_SIZE;
+    if truncated_stderr {
+        stderr.truncate(MAX_OUTPUT_SIZE);
+    };
+
+    session.reply(Item{
+        exit_status,
+        stdout,
+        stderr,
+        truncated_stdout,
+        truncated_stderr,
+    })?;
+
     Ok(())
 }
 
@@ -114,4 +211,279 @@ impl crate::response::Item for Item {
 
         proto
     }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use std::path::PathBuf;
+
+    use ed25519_dalek::{Signer, VerifyingKey};
+
+    use crate::session::FakeSession;
+
+    use super::*;
+
+    fn prepare_session(verification_key: VerifyingKey) -> FakeSession {
+        crate::session::FakeSession::with_args(crate::args::Args {
+            heartbeat_rate: std::time::Duration::from_secs(0),
+            command_verification_key: Some(verification_key),
+            verbosity: log::LevelFilter::Debug,
+            log_to_stdout: false,
+            log_to_file: None,
+        })
+    }
+
+    #[test]
+    fn test_args() {
+        let signing_key = ed25519_dalek::SigningKey::generate(&mut rand::rngs::OsRng);
+        let mut session = prepare_session(signing_key.verifying_key());
+
+        let mut command = rrg_proto::execute_signed_command::SignedCommand::new();
+
+        #[cfg(target_family = "unix")] {
+            command.set_path(rrg_proto::fs::Path::try_from(PathBuf::from("echo")).unwrap());
+        }
+        #[cfg(target_os = "windows")] {
+            command.set_path(rrg_proto::fs::Path::try_from(PathBuf::from("cmd")).unwrap());
+            command.args.push(String::from("/C"));
+            command.args.push(String::from("echo"));
+        }
+        command.args.push(String::from("Hello,"));
+        command.args.push(String::from("world!"));
+
+        let raw_command = command.write_to_bytes().unwrap();
+        let ed25519_signature = signing_key.sign(&raw_command);
+
+        let args = Args {
+            raw_command,
+            command,
+            ed25519_signature,
+            stdin: Stdin::NONE,
+            timeout: std::time::Duration::from_secs(5),
+        };
+        handle(&mut session, args).unwrap();
+        let item = session.reply::<Item>(0);
+
+        assert!(!item.truncated_stdout);
+        assert!(!item.truncated_stderr);
+        assert!(item.stderr.is_empty());
+        #[cfg(target_family = "unix")]
+        assert_eq!(String::from_utf8_lossy(&item.stdout), format!("Hello, world!\n"));
+        #[cfg(target_os = "windows")]
+        assert_eq!(String::from_utf8_lossy(&item.stdout), format!("Hello, world!\r\n"));
+        assert!(item.exit_status.success())
+    }
+
+    #[test]
+    fn test_stdin() {
+        let signing_key = ed25519_dalek::SigningKey::generate(&mut rand::rngs::OsRng);
+        let mut session = prepare_session(signing_key.verifying_key());
+
+        let stdin = Stdin::SIGNED(Vec::<u8>::from("Hello, world!"));
+
+        let mut command = rrg_proto::execute_signed_command::SignedCommand::new();
+
+        #[cfg(target_family = "unix")]
+        command.set_path(rrg_proto::fs::Path::try_from(PathBuf::from("cat")).unwrap());
+
+        #[cfg(target_os = "windows")] {
+            command.set_path(rrg_proto::fs::Path::try_from(PathBuf::from("cmd")).unwrap());
+            command.args.push(String::from("/C"));
+            command.args.push(String::from("findstr ."));
+        }
+
+        let raw_command = command.write_to_bytes().unwrap();
+        let ed25519_signature = signing_key.sign(&raw_command);
+
+        let args = Args {
+            raw_command,
+            command,
+            ed25519_signature,
+            stdin,
+            timeout: std::time::Duration::from_secs(5),
+        };
+        handle(&mut session, args).unwrap();
+        let item = session.reply::<Item>(0);
+
+        assert!(!item.truncated_stdout);
+        assert!(!item.truncated_stderr);
+        assert!(item.stderr.is_empty());
+        #[cfg(target_family = "unix")]
+        assert_eq!(String::from_utf8_lossy(&item.stdout), format!("Hello, world!"));
+        #[cfg(target_os = "windows")]
+        assert_eq!(String::from_utf8_lossy(&item.stdout), format!("Hello, world!\r\n"));
+        assert!(item.exit_status.success());
+    }
+
+    #[test]
+    fn test_env() {
+        let signing_key = ed25519_dalek::SigningKey::generate(&mut rand::rngs::OsRng);
+        let mut session = prepare_session(signing_key.verifying_key());
+
+        let mut command = rrg_proto::execute_signed_command::SignedCommand::new();
+        command.set_path(rrg_proto::fs::Path::try_from(PathBuf::from("printenv")).unwrap());
+        command.env.insert(String::from("MY_ENV_VAR"), String::from("Hello, world!"));
+
+        let raw_command = command.write_to_bytes().unwrap();
+        let ed25519_signature = signing_key.sign(&raw_command);
+
+        let args = Args {
+            raw_command,
+            command,
+            ed25519_signature,
+            stdin: Stdin::NONE,
+            timeout: std::time::Duration::from_secs(5),
+        };
+        handle(&mut session, args).unwrap();
+        let item = session.reply::<Item>(0);
+
+        assert!(!item.truncated_stdout);
+        assert!(!item.truncated_stderr);
+        assert!(item.stderr.is_empty());
+        assert!(String::from_utf8_lossy(&item.stdout).find("MY_ENV_VAR=Hello, world!").is_some());
+        assert!(item.exit_status.success());
+    }
+
+    #[test]
+    fn test_unsigned_stdin() {
+        let signing_key = ed25519_dalek::SigningKey::generate(&mut rand::rngs::OsRng);
+        let mut session = prepare_session(signing_key.verifying_key());
+
+        let stdin = Stdin::UNSIGNED(Vec::<u8>::from("Hello, world!"));
+
+        let mut command = rrg_proto::execute_signed_command::SignedCommand::new();
+        command.set_unsigned_stdin(true);
+
+        #[cfg(target_family = "unix")]
+        command.set_path(rrg_proto::fs::Path::try_from(PathBuf::from("cat")).unwrap());
+
+        #[cfg(target_os = "windows")] {
+            command.set_path(rrg_proto::fs::Path::try_from(PathBuf::from("cmd")).unwrap());
+            command.args.push(String::from("/C"));
+            command.args.push(String::from("findstr ."));
+        }
+
+        let raw_command = command.write_to_bytes().unwrap();
+        let ed25519_signature = signing_key.sign(&raw_command);
+
+        let args = Args {
+            raw_command,
+            command,
+            ed25519_signature,
+            stdin,
+            timeout: std::time::Duration::from_secs(5),
+        };
+
+        handle(&mut session, args).unwrap();
+        let item = session.reply::<Item>(0);
+
+        assert!(!item.truncated_stdout);
+        assert!(!item.truncated_stderr);
+        // assert!(item.stderr.is_empty());
+        #[cfg(target_family = "unix")]
+        assert_eq!(String::from_utf8_lossy(&item.stdout), format!("Hello, world!"));
+        #[cfg(target_os = "windows")]
+        assert_eq!(String::from_utf8_lossy(&item.stdout), format!("Hello, world!\r\n"));
+        assert!(item.exit_status.success());
+    }   
+
+    #[test]
+    fn test_invalid_signature() {
+        let signing_key = ed25519_dalek::SigningKey::generate(&mut rand::rngs::OsRng);
+        let mut session = prepare_session(signing_key.verifying_key());
+
+        let mut command = rrg_proto::execute_signed_command::SignedCommand::new();
+        command.set_path(rrg_proto::fs::Path::try_from(PathBuf::from("ls")).unwrap());
+
+        let raw_command = command.write_to_bytes().unwrap();
+
+        let invalid_signature_bytes: [u8; 64] = [4_u8; 64]; //  random bytes.
+        let invalid_signature = ed25519_dalek::Signature::from_bytes(&invalid_signature_bytes);
+
+        let args = Args {
+            raw_command,
+            command,
+            ed25519_signature: invalid_signature,
+            stdin: Stdin::NONE,
+            timeout: std::time::Duration::from_secs(5),
+        };
+
+        let _ = handle(&mut session, args).is_err();
+    }
+
+    #[test]
+    fn test_truncated_output() {
+        let signing_key = ed25519_dalek::SigningKey::generate(&mut rand::rngs::OsRng);
+        let mut session = prepare_session(signing_key.verifying_key());
+
+        let mut command = rrg_proto::execute_signed_command::SignedCommand::new();
+
+        #[cfg(target_family = "unix")] 
+        command.set_path(rrg_proto::fs::Path::try_from(PathBuf::from("echo")).unwrap());
+        
+        #[cfg(target_os = "windows")] {
+            command.set_path(rrg_proto::fs::Path::try_from(PathBuf::from("cmd")).unwrap());
+            command.args.push(String::from("/C"));
+            command.args.push(String::from("echo"));
+        }
+
+        command.args.push("A".repeat(MAX_OUTPUT_SIZE) + "truncated");
+
+        let raw_command = command.write_to_bytes().unwrap();
+        let ed25519_signature = signing_key.sign(&raw_command);
+
+        let args = Args {
+            raw_command,
+            command,
+            ed25519_signature,
+            stdin: Stdin::NONE,
+            timeout: std::time::Duration::from_secs(5),
+        };
+
+        handle(&mut session, args).unwrap();
+        let item = session.reply::<Item>(0);
+
+        assert!(item.truncated_stdout);
+        assert!(!item.truncated_stderr);
+        assert!(item.stderr.is_empty());
+        assert_eq!(String::from_utf8_lossy(&item.stdout), "A".repeat(MAX_OUTPUT_SIZE));
+        assert!(item.exit_status.success());
+    }
+
+    #[test]
+    fn test_timeout() {
+        let timeout = std::time::Duration::from_secs(5);
+
+        let signing_key = ed25519_dalek::SigningKey::generate(&mut rand::rngs::OsRng);
+        let mut session = prepare_session(signing_key.verifying_key());
+
+        let mut command = rrg_proto::execute_signed_command::SignedCommand::new();
+        command.set_path(rrg_proto::fs::Path::try_from(PathBuf::from("sleep")).unwrap());
+        command.args.push((timeout.as_secs() + 1).to_string());
+
+        let raw_command = command.write_to_bytes().unwrap();
+        let ed25519_signature = signing_key.sign(&raw_command);
+
+        let args = Args {
+            raw_command,
+            command,
+            ed25519_signature,
+            stdin: Stdin::NONE,
+            timeout,
+        };
+
+        handle(&mut session, args).unwrap();
+        let item = session.reply::<Item>(0);
+
+        assert!(item.stderr.is_empty());
+        assert!(item.stdout.is_empty());
+        assert!(!item.exit_status.success());
+        #[cfg(target_family = "unix")]
+        {
+            use std::os::unix::process::ExitStatusExt;
+
+            assert_eq!(item.exit_status.signal(), Some(9)); // killed
+        }
+    }
 }
\ No newline at end of file