tor_cert/
rsa.rs

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::{ExternallySigned, timed::TimerangeBound};
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 a reference to the digest.
40    pub fn digest(&self) -> &[u8; 32] {
41        &self.digest
42    }
43
44    /// Return true if the subject key in this certificate matches `other`
45    pub fn subject_key_matches(&self, other: &ll::pk::ed25519::Ed25519Identity) -> bool {
46        other == &self.subject_key
47    }
48
49    /// Decode a slice of bytes into an RSA crosscert.
50    pub fn decode(bytes: &[u8]) -> tor_bytes::Result<UncheckedRsaCrosscert> {
51        let mut r = Reader::from_slice(bytes);
52        let signed_portion = r.peek(36)?; // TODO(nickm): a bit ugly.
53        let subject_key = r.extract()?;
54        let exp_hours = r.take_u32()?;
55        let siglen = r.take_u8()?;
56        let signature = r.take(siglen as usize)?.into();
57
58        let mut d = ll::d::Sha256::new();
59        d.update(&b"Tor TLS RSA/Ed25519 cross-certificate"[..]);
60        d.update(signed_portion);
61        let digest = d.finalize().into();
62
63        let cc = RsaCrosscert {
64            subject_key,
65            exp_hours,
66            digest,
67            signature,
68        };
69
70        Ok(UncheckedRsaCrosscert(cc))
71    }
72}
73
74/// An RsaCrosscert whose signature has not been checked.
75pub struct UncheckedRsaCrosscert(RsaCrosscert);
76
77impl ExternallySigned<TimerangeBound<RsaCrosscert>> for UncheckedRsaCrosscert {
78    type Key = ll::pk::rsa::PublicKey;
79    type KeyHint = ();
80    type Error = tor_bytes::Error;
81
82    fn key_is_correct(&self, _k: &Self::Key) -> Result<(), Self::KeyHint> {
83        // there is no way to check except for trying to verify the signature
84        Ok(())
85    }
86
87    fn is_well_signed(&self, k: &Self::Key) -> Result<(), Self::Error> {
88        k.verify(&self.0.digest[..], &self.0.signature[..])
89            .map_err(|_| {
90                tor_bytes::Error::InvalidMessage(
91                    "Invalid signature on RSA->Ed identity crosscert".into(),
92                )
93            })?;
94        Ok(())
95    }
96
97    fn dangerously_assume_wellsigned(self) -> TimerangeBound<RsaCrosscert> {
98        let expiration = self.0.expiry();
99        TimerangeBound::new(self.0, ..expiration)
100    }
101}
tor_cert/rsa.rs

tor_cert/
rsa.rs
