tor_key_forge/
ssh.rs

Help
1//! Shared OpenSSH helpers.
2
3use ssh_key::{
4    private::KeypairData, public::KeyData, Algorithm, LineEnding, PrivateKey, PublicKey,
5};
6use tor_error::{internal, into_internal};
7use tor_llcrypto::pk::{curve25519, ed25519};
8
9use crate::{ErasedKey, Error, KeyType, Result};
10
11/// The algorithm string for x25519 SSH keys.
12///
13/// See <https://spec.torproject.org/ssh-protocols.html>
14pub(crate) const X25519_ALGORITHM_NAME: &str = "x25519@spec.torproject.org";
15
16/// The algorithm string for expanded ed25519 SSH keys.
17///
18/// See <https://spec.torproject.org/ssh-protocols.html>
19pub(crate) const ED25519_EXPANDED_ALGORITHM_NAME: &str = "ed25519-expanded@spec.torproject.org";
20
21/// SSH key algorithms.
22//
23// Note: this contains all the types supported by ssh_key, plus variants representing
24// x25519 and expanded ed25519 keys.
25#[derive(Clone, Debug, PartialEq, derive_more::Display)]
26#[non_exhaustive]
27pub enum SshKeyAlgorithm {
28    /// Digital Signature Algorithm
29    Dsa,
30    /// Elliptic Curve Digital Signature Algorithm
31    Ecdsa,
32    /// Ed25519
33    Ed25519,
34    /// Expanded Ed25519
35    Ed25519Expanded,
36    /// X25519
37    X25519,
38    /// RSA
39    Rsa,
40    /// FIDO/U2F key with ECDSA/NIST-P256 + SHA-256
41    SkEcdsaSha2NistP256,
42    /// FIDO/U2F key with Ed25519
43    SkEd25519,
44    /// An unrecognized [`ssh_key::Algorithm`].
45    Unknown(ssh_key::Algorithm),
46}
47
48impl From<Algorithm> for SshKeyAlgorithm {
49    fn from(algo: Algorithm) -> SshKeyAlgorithm {
50        match &algo {
51            Algorithm::Dsa => SshKeyAlgorithm::Dsa,
52            Algorithm::Ecdsa { .. } => SshKeyAlgorithm::Ecdsa,
53            Algorithm::Ed25519 => SshKeyAlgorithm::Ed25519,
54            Algorithm::Rsa { .. } => SshKeyAlgorithm::Rsa,
55            Algorithm::SkEcdsaSha2NistP256 => SshKeyAlgorithm::SkEcdsaSha2NistP256,
56            Algorithm::SkEd25519 => SshKeyAlgorithm::SkEd25519,
57            Algorithm::Other(name) => match name.as_str() {
58                X25519_ALGORITHM_NAME => SshKeyAlgorithm::X25519,
59                ED25519_EXPANDED_ALGORITHM_NAME => SshKeyAlgorithm::Ed25519Expanded,
60                _ => SshKeyAlgorithm::Unknown(algo),
61            },
62            // Note: ssh_key::Algorithm is non_exhaustive, so we need this catch-all variant
63            _ => SshKeyAlgorithm::Unknown(algo),
64        }
65    }
66}
67
68/// Convert ssh_key KeyData or KeypairData to one of our key types.
69macro_rules! ssh_to_internal_erased {
70    (PRIVATE $key:expr, $algo:expr) => {{
71        ssh_to_internal_erased!(
72            $key,
73            $algo,
74            convert_ed25519_kp,
75            convert_expanded_ed25519_kp,
76            convert_x25519_kp,
77            KeypairData
78        )
79    }};
80
81    (PUBLIC $key:expr, $algo:expr) => {{
82        ssh_to_internal_erased!(
83            $key,
84            $algo,
85            convert_ed25519_pk,
86            convert_expanded_ed25519_pk,
87            convert_x25519_pk,
88            KeyData
89        )
90    }};
91
92    ($key:expr, $algo:expr, $ed25519_fn:path, $expanded_ed25519_fn:path, $x25519_fn:path, $key_data_ty:tt) => {{
93        let key = $key;
94        let algo = SshKeyAlgorithm::from($algo);
95
96        // Build the expected key type (i.e. convert ssh_key key types to the key types
97        // we're using internally).
98        match key {
99            $key_data_ty::Ed25519(key) => Ok($ed25519_fn(&key).map(Box::new)?),
100            $key_data_ty::Other(other) => match algo {
101                SshKeyAlgorithm::X25519 => Ok($x25519_fn(&other).map(Box::new)?),
102                SshKeyAlgorithm::Ed25519Expanded => Ok($expanded_ed25519_fn(&other).map(Box::new)?),
103                _ => Err(Error::UnsupportedKeyAlgorithm(algo)),
104            },
105            _ => Err(Error::UnsupportedKeyAlgorithm(algo)),
106        }
107    }};
108}
109
110/// Try to convert an [`Ed25519Keypair`](ssh_key::private::Ed25519Keypair) to an [`ed25519::Keypair`].
111// TODO remove this allow?
112// clippy wants this whole function to be infallible because
113// nowadays ed25519::Keypair can be made infallibly from bytes,
114// but is that really right?
115#[allow(clippy::unnecessary_fallible_conversions)]
116fn convert_ed25519_kp(key: &ssh_key::private::Ed25519Keypair) -> Result<ed25519::Keypair> {
117    Ok(ed25519::Keypair::try_from(&key.private.to_bytes())
118        .map_err(|_| internal!("bad ed25519 keypair"))?)
119}
120
121/// Try to convert an [`OpaqueKeypair`](ssh_key::private::OpaqueKeypair) to a [`curve25519::StaticKeypair`].
122fn convert_x25519_kp(key: &ssh_key::private::OpaqueKeypair) -> Result<curve25519::StaticKeypair> {
123    let public: [u8; 32] = key
124        .public
125        .as_ref()
126        .try_into()
127        .map_err(|_| internal!("bad x25519 public key length"))?;
128
129    let secret: [u8; 32] = key
130        .private
131        .as_ref()
132        .try_into()
133        .map_err(|_| internal!("bad x25519 secret key length"))?;
134
135    Ok(curve25519::StaticKeypair {
136        public: public.into(),
137        secret: secret.into(),
138    })
139}
140
141/// Try to convert an [`OpaqueKeypair`](ssh_key::private::OpaqueKeypair) to an [`ed25519::ExpandedKeypair`].
142fn convert_expanded_ed25519_kp(
143    key: &ssh_key::private::OpaqueKeypair,
144) -> Result<ed25519::ExpandedKeypair> {
145    let public = ed25519::PublicKey::try_from(key.public.as_ref())
146        .map_err(|_| internal!("bad expanded ed25519 public key "))?;
147
148    let keypair = ed25519::ExpandedKeypair::from_secret_key_bytes(
149        key.private
150            .as_ref()
151            .try_into()
152            .map_err(|_| internal!("bad length on expanded ed25519 secret key ",))?,
153    )
154    .ok_or_else(|| internal!("bad expanded ed25519 secret key "))?;
155
156    if &public != keypair.public() {
157        return Err(internal!("mismatched ed25519 keypair",).into());
158    }
159
160    Ok(keypair)
161}
162
163/// Try to convert an [`Ed25519PublicKey`](ssh_key::public::Ed25519PublicKey) to an [`ed25519::PublicKey`].
164fn convert_ed25519_pk(key: &ssh_key::public::Ed25519PublicKey) -> Result<ed25519::PublicKey> {
165    Ok(ed25519::PublicKey::from_bytes(key.as_ref())
166        .map_err(|_| internal!("bad ed25519 public key "))?)
167}
168
169/// Try to convert an [`OpaquePublicKey`](ssh_key::public::OpaquePublicKey) to an [`ed25519::PublicKey`].
170///
171/// This function always returns an error because the custom `ed25519-expanded@spec.torproject.org`
172/// SSH algorithm should not be used for ed25519 public keys (only for expanded ed25519 key
173/// _pairs_). This function is needed for the [`ssh_to_internal_erased!`] macro.
174fn convert_expanded_ed25519_pk(
175    _key: &ssh_key::public::OpaquePublicKey,
176) -> Result<ed25519::PublicKey> {
177    Err(internal!(
178        "invalid ed25519 public key (ed25519 public keys should be stored as ssh-ed25519)",
179    )
180    .into())
181}
182
183/// Try to convert an [`OpaquePublicKey`](ssh_key::public::OpaquePublicKey) to a [`curve25519::PublicKey`].
184fn convert_x25519_pk(key: &ssh_key::public::OpaquePublicKey) -> Result<curve25519::PublicKey> {
185    let public: [u8; 32] = key
186        .as_ref()
187        .try_into()
188        .map_err(|_| internal!("bad x25519 public key length"))?;
189
190    Ok(curve25519::PublicKey::from(public))
191}
192
193/// A public key or a keypair.
194#[derive(Clone, Debug)]
195#[non_exhaustive]
196pub struct SshKeyData(SshKeyDataInner);
197
198/// The inner representation of a public key or a keypair.
199#[derive(Clone, Debug)]
200#[non_exhaustive]
201enum SshKeyDataInner {
202    /// The [`KeyData`] of a public key.
203    Public(KeyData),
204    /// The [`KeypairData`] of a private key.
205    Private(KeypairData),
206}
207
208impl SshKeyData {
209    /// Try to convert a [`KeyData`] to [`SshKeyData`].
210    ///
211    /// Returns an error if this type of [`KeyData`] is not supported.
212    pub fn try_from_key_data(key: KeyData) -> Result<Self> {
213        let algo = SshKeyAlgorithm::from(key.algorithm());
214        let () = match key {
215            KeyData::Ed25519(_) => Ok(()),
216            KeyData::Other(_) => match algo {
217                SshKeyAlgorithm::X25519 => Ok(()),
218                _ => Err(Error::UnsupportedKeyAlgorithm(algo)),
219            },
220            _ => Err(Error::UnsupportedKeyAlgorithm(algo)),
221        }?;
222
223        Ok(Self(SshKeyDataInner::Public(key)))
224    }
225
226    /// Try to convert a [`KeypairData`] to [`SshKeyData`].
227    ///
228    /// Returns an error if this type of [`KeypairData`] is not supported.
229    pub fn try_from_keypair_data(key: KeypairData) -> Result<Self> {
230        let algo = SshKeyAlgorithm::from(
231            key.algorithm()
232                .map_err(into_internal!("encrypted keys are not yet supported"))?,
233        );
234        let () = match key {
235            KeypairData::Ed25519(_) => Ok(()),
236            KeypairData::Other(_) => match algo {
237                SshKeyAlgorithm::X25519 => Ok(()),
238                SshKeyAlgorithm::Ed25519Expanded => Ok(()),
239                _ => Err(Error::UnsupportedKeyAlgorithm(algo)),
240            },
241            _ => Err(Error::UnsupportedKeyAlgorithm(algo)),
242        }?;
243
244        Ok(Self(SshKeyDataInner::Private(key)))
245    }
246
247    /// Encode this key as an OpenSSH-formatted key using the specified `comment`
248    pub fn to_openssh_string(&self, comment: &str) -> Result<String> {
249        let openssh_key = match &self.0 {
250            SshKeyDataInner::Public(key_data) => {
251                let openssh_key = PublicKey::new(key_data.clone(), comment);
252
253                openssh_key
254                    .to_openssh()
255                    .map_err(|_| tor_error::internal!("failed to encode SSH key"))?
256            }
257            SshKeyDataInner::Private(keypair) => {
258                let openssh_key = PrivateKey::new(keypair.clone(), comment)
259                    .map_err(|_| tor_error::internal!("failed to create SSH private key"))?;
260
261                openssh_key
262                    .to_openssh(LineEnding::LF)
263                    .map_err(|_| tor_error::internal!("failed to encode SSH key"))?
264                    .to_string()
265            }
266        };
267
268        Ok(openssh_key)
269    }
270
271    /// Convert the key material into a known key type,
272    /// and return the type-erased value.
273    ///
274    /// The caller is expected to downcast the value returned to the correct concrete type.
275    pub fn into_erased(self) -> Result<ErasedKey> {
276        match self.0 {
277            SshKeyDataInner::Private(key) => {
278                let algorithm = key
279                    .algorithm()
280                    .map_err(into_internal!("unsupported key type"))?;
281                ssh_to_internal_erased!(PRIVATE key, algorithm)
282            }
283            SshKeyDataInner::Public(key) => {
284                let algorithm = key.algorithm();
285                ssh_to_internal_erased!(PUBLIC key, algorithm)
286            }
287        }
288    }
289
290    /// Return the [`KeyType`] of this OpenSSH key.
291    ///
292    /// Returns an error if the underlying key material is [`KeypairData::Encrypted`],
293    /// or if its algorithm is unsupported.
294    pub fn key_type(&self) -> Result<KeyType> {
295        match &self.0 {
296            SshKeyDataInner::Public(k) => KeyType::try_from_key_data(k),
297            SshKeyDataInner::Private(k) => KeyType::try_from_keypair_data(k),
298        }
299    }
300}
tor_key_forge/ssh.rs

tor_key_forge/
ssh.rs
