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//! Generate SSH host keys and certificates.
use std::fs::{read, File, Permissions};
use std::io::Write;
use std::os::unix::fs::PermissionsExt;
use std::path::Path;
use std::process::Command;
use tempfile::tempdir;
/// Errors from this module.
#[derive(Debug, thiserror::Error)]
pub enum KeyError {
/// Could not generate a new key pair.
#[error("ssh-keygen failed to generate a key: {0}")]
KeyGen(String),
/// Error creating a certificate.
#[error("ssh-keygen failed to certify a key: {0}")]
CertError(String),
/// I/O error.
#[error(transparent)]
IoError(#[from] std::io::Error),
/// Error parsing a string as UTF8.
#[error(transparent)]
Utf8Error(#[from] std::string::FromUtf8Error),
}
/// Type of SSH key.
pub enum KeyKind {
/// RSA key of desired length in bits.
RSA(u32),
/// DSA of fixed length.
DSA,
/// ECDSA key of 256 bits.
ECDSA256,
/// ECDSA key of 384 bits.
ECDSA384,
/// ECDSA key of 521 bits.
ECDSA521,
/// Ed25519 key of fixed length.
Ed25519,
}
impl KeyKind {
/// Type of key as string for ssh-keygen -t option.
pub fn as_str(&self) -> &str {
match self {
Self::RSA(_) => "rsa",
Self::DSA => "dsa",
Self::ECDSA256 => "ecdsa",
Self::ECDSA384 => "ecdsa",
Self::ECDSA521 => "ecdsa",
Self::Ed25519 => "ed25519",
}
}
/// Number of bits needed for the key.
///
/// This is only really meaningful for RSA keys.
pub fn bits(&self) -> u32 {
match self {
Self::RSA(bits) => *bits,
Self::DSA => 1024,
Self::ECDSA256 => 256,
Self::ECDSA384 => 384,
Self::ECDSA521 => 521,
Self::Ed25519 => 1024,
}
}
}
/// A public/private key pair.
pub struct KeyPair {
public: String,
private: String,
}
impl KeyPair {
/// Create pair from string representation.
pub fn from_str(public: String, private: String) -> Self {
Self { private, public }
}
/// Generate a new key pair of the desired kind.
pub fn generate(kind: KeyKind) -> Result<Self, KeyError> {
let dirname = tempdir()?;
let private_key = dirname.path().join("key");
let output = Command::new("ssh-keygen")
.arg("-f")
.arg(&private_key)
.arg("-t")
.arg(kind.as_str())
.arg("-b")
.arg(format!("{}", kind.bits()))
.arg("-N")
.arg("")
.output()?;
if !output.status.success() {
let stderr = String::from_utf8_lossy(&output.stderr).into_owned();
return Err(KeyError::KeyGen(stderr));
}
let public_key = private_key.with_extension("pub");
Ok(Self::from_str(
read_string(&public_key)?,
read_string(&private_key)?,
))
}
/// Public key of the pair, as a string.
pub fn public(&self) -> &str {
&self.public
}
/// Private key of the pair, as a string.
pub fn private(&self) -> &str {
&self.private
}
}
fn read_string(filename: &Path) -> Result<String, KeyError> {
let bytes = read(filename)?;
Ok(String::from_utf8(bytes)?)
}
/// A key for SSH certificate authority.
///
/// This is used for creating host certificates.
pub struct CaKey {
private: String,
}
impl CaKey {
/// Create new CA key from a key pair.
pub fn from(pair: KeyPair) -> Self {
Self {
private: pair.private().to_string(),
}
}
/// Read CA key from a file.
pub fn from_file(filename: &Path) -> Result<Self, KeyError> {
let private = read_string(filename)?;
Ok(Self { private })
}
/// Create a host certificate.
///
/// Return as a string.
pub fn certify_host(&self, host_key: &KeyPair, hostname: &str) -> Result<String, KeyError> {
let dirname = tempdir()?;
let ca_key = dirname.path().join("ca");
let host_key_pub = dirname.path().join("host.pub");
let cert = dirname.path().join("host-cert.pub");
write_string(&ca_key, &self.private)?;
write_string(&host_key_pub, host_key.public())?;
let output = Command::new("ssh-keygen")
.arg("-s")
.arg(&ca_key)
.arg("-h")
.arg("-n")
.arg(hostname)
.arg("-I")
.arg(format!("host key for {}", hostname))
.arg(&host_key_pub)
.output()?;
if !output.status.success() {
let stderr = String::from_utf8_lossy(&output.stderr).into_owned();
return Err(KeyError::CertError(stderr));
}
Ok(read_string(&cert)?)
}
}
fn write_string(filename: &Path, s: &str) -> Result<(), KeyError> {
let mut file = File::create(filename)?;
let ro_user = Permissions::from_mode(0o600);
file.set_permissions(ro_user)?;
file.write_all(s.as_bytes())?;
Ok(())
}
#[cfg(test)]
mod keypair_test {
use super::{CaKey, KeyKind, KeyPair};
#[test]
fn generate_key() {
let pair = KeyPair::generate(KeyKind::Ed25519).unwrap();
assert_ne!(pair.public(), "");
assert_ne!(pair.private(), "");
assert_ne!(pair.private(), pair.public());
}
#[test]
fn certify_host_key() {
let ca = KeyPair::generate(KeyKind::Ed25519).unwrap();
let ca = CaKey::from(ca);
let host = KeyPair::generate(KeyKind::Ed25519).unwrap();
let cert = ca.certify_host(&host, "dummy").unwrap();
assert_ne!(cert, "");
}
}
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