tor_cert/
rsa.rs

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1//! RSA->Ed25519 cross-certificates
2//!
3//! These are used in the Tor link handshake to prove that a given ed25519
4//! key speaks for a given (deprecated) RSA identity.
5
6use tor_bytes::Reader;
7use tor_checkable::{timed::TimerangeBound, ExternallySigned};
8use tor_llcrypto as ll;
9
10use digest::Digest;
11
12/// A RSA->Ed25519 cross-certificate
13///
14/// This kind of certificate is used in the channel handshake to prove
15/// that the Ed25519 identity key speaks on behalf of the RSA identity key.
16///
17/// (There is no converse type for certifying Ed25519 identity keys with
18/// RSA identity keys, since the RSA identity keys are too weak to trust.)
19#[must_use]
20pub struct RsaCrosscert {
21    /// The key that is being certified
22    subject_key: ll::pk::ed25519::Ed25519Identity,
23    /// The expiration time of this certificate, in hours since the
24    /// unix epoch.
25    exp_hours: u32,
26    /// The digest of the signed part of the certificate (for checking)
27    digest: [u8; 32],
28    /// The (alleged) signature on the certificate.
29    signature: Vec<u8>,
30}
31
32impl RsaCrosscert {
33    /// Return the time at which this certificate becomes expired
34    pub fn expiry(&self) -> std::time::SystemTime {
35        let d = std::time::Duration::new(u64::from(self.exp_hours) * 3600, 0);
36        std::time::SystemTime::UNIX_EPOCH + d
37    }
38
39    /// Return true if the subject key in this certificate matches `other`
40    pub fn subject_key_matches(&self, other: &ll::pk::ed25519::Ed25519Identity) -> bool {
41        other == &self.subject_key
42    }
43
44    /// Decode a slice of bytes into an RSA crosscert.
45    pub fn decode(bytes: &[u8]) -> tor_bytes::Result<UncheckedRsaCrosscert> {
46        let mut r = Reader::from_slice(bytes);
47        let signed_portion = r.peek(36)?; // TODO(nickm): a bit ugly.
48        let subject_key = r.extract()?;
49        let exp_hours = r.take_u32()?;
50        let siglen = r.take_u8()?;
51        let signature = r.take(siglen as usize)?.into();
52
53        let mut d = ll::d::Sha256::new();
54        d.update(&b"Tor TLS RSA/Ed25519 cross-certificate"[..]);
55        d.update(signed_portion);
56        let digest = d.finalize().into();
57
58        let cc = RsaCrosscert {
59            subject_key,
60            exp_hours,
61            digest,
62            signature,
63        };
64
65        Ok(UncheckedRsaCrosscert(cc))
66    }
67}
68
69/// An RsaCrosscert whose signature has not been checked.
70pub struct UncheckedRsaCrosscert(RsaCrosscert);
71
72impl ExternallySigned<TimerangeBound<RsaCrosscert>> for UncheckedRsaCrosscert {
73    type Key = ll::pk::rsa::PublicKey;
74    type KeyHint = ();
75    type Error = tor_bytes::Error;
76
77    fn key_is_correct(&self, _k: &Self::Key) -> Result<(), Self::KeyHint> {
78        // there is no way to check except for trying to verify the signature
79        Ok(())
80    }
81
82    fn is_well_signed(&self, k: &Self::Key) -> Result<(), Self::Error> {
83        k.verify(&self.0.digest[..], &self.0.signature[..])
84            .map_err(|_| {
85                tor_bytes::Error::InvalidMessage(
86                    "Invalid signature on RSA->Ed identity crosscert".into(),
87                )
88            })?;
89        Ok(())
90    }
91
92    fn dangerously_assume_wellsigned(self) -> TimerangeBound<RsaCrosscert> {
93        let expiration = self.0.expiry();
94        TimerangeBound::new(self.0, ..expiration)
95    }
96}
tor_cert/rsa.rs

tor_cert/
rsa.rs
