1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
//! # SCT.rs: SCT verification library
//! This library implements verification of Signed Certificate Timestamps.
//! These are third-party assurances that a particular certificate has
//! been included in a Certificate Transparency log.
//!
//! See RFC6962 for the details of the formats implemented here.
//!
//! It is intended to be useful to libraries which perform certificate
//! validation, OCSP libraries, and TLS libraries.

#![forbid(unsafe_code,
          unstable_features)]
#![deny(trivial_casts,
        trivial_numeric_casts,
        missing_docs,
        unused_import_braces,
        unused_extern_crates,
        unused_qualifications)]

#![no_std]

extern crate alloc;

use alloc::vec::Vec;

/// Describes a CT log
///
/// This structure contains some metadata fields not used by the library.
/// Rationale: it makes sense to keep this metadata with the other
/// values for review purposes.
#[derive(Debug)]
pub struct Log<'a> {
    /// The operator's name/description of the log.
    /// This field is not used by the library.
    pub description: &'a str,

    /// The certificate submission url.
    /// This field is not used by the library.
    pub url: &'a str,

    /// Which entity operates the log.
    /// This field is not used by the library.
    pub operated_by: &'a str,

    /// Public key usable for verifying certificates.
    /// TODO: fixme format of this; should be a SPKI
    /// so the `id` is verifiable, but currently is a
    /// raw public key (like, an ECPoint or RSAPublicKey).
    pub key: &'a [u8],

    /// Key hash, which is SHA256 applied to the SPKI
    /// encoding.
    pub id: [u8; 32],

    /// The log's maximum merge delay.
    /// This field is not used by the library.
    pub max_merge_delay: usize
}

/// How sct.rs reports errors.
#[derive(Debug, PartialEq, Clone, Copy)]
pub enum Error {
    /// The SCT was somehow misencoded, truncated or otherwise corrupt.
    MalformedSCT,

    /// The SCT contained an invalid signature.
    InvalidSignature,

    /// The SCT was signed in the future.  Clock skew?
    TimestampInFuture,

    /// The SCT had a version that this library does not handle.
    UnsupportedSCTVersion,

    /// The SCT was refers to an unknown log.
    UnknownLog,
}

impl Error {
    /// Applies a suggested policy for error handling:
    ///
    /// Returns `true` if the error should end processing
    /// for whatever the SCT is attached to (like, abort a TLS
    /// handshake).
    ///
    /// Returns `false` if this error should be a 'soft failure'
    /// -- the SCT is unverifiable with this library and set of
    /// logs.
    pub fn should_be_fatal(&self) -> bool {
        match *self {
            Error::UnknownLog
                | Error::UnsupportedSCTVersion => false,
            _ => true
        }
    }
}

fn lookup(logs: &[&Log], id: &[u8]) -> Result<usize, Error> {
    for (i, l) in logs.iter().enumerate() {
        if id == &l.id {
            return Ok(i);
        }
    }

    Err(Error::UnknownLog)
}

fn decode_u64(inp: untrusted::Input) -> u64 {
    let b = inp.as_slice_less_safe();
    assert_eq!(b.len(), 8);
    (b[0] as u64) << 56 |
        (b[1] as u64) << 48 |
        (b[2] as u64) << 40 |
        (b[3] as u64) << 32 |
        (b[4] as u64) << 24 |
        (b[5] as u64) << 16 |
        (b[6] as u64) << 8 |
        (b[7] as u64)
}

fn decode_u16(inp: untrusted::Input) -> u16 {
    let b = inp.as_slice_less_safe();
    assert_eq!(b.len(), 2);
    (b[0] as u16) << 8 | (b[1] as u16)
}

fn write_u64(v: u64, out: &mut Vec<u8>) {
    out.push((v >> 56) as u8);
    out.push((v >> 48) as u8);
    out.push((v >> 40) as u8);
    out.push((v >> 32) as u8);
    out.push((v >> 24) as u8);
    out.push((v >> 16) as u8);
    out.push((v >> 8) as u8);
    out.push(v as u8);
}

fn write_u24(v: u32, out: &mut Vec<u8>) {
    out.push((v >> 16) as u8);
    out.push((v >> 8) as u8);
    out.push(v as u8);
}

fn write_u16(v: u16, out: &mut Vec<u8>) {
    out.push((v >> 8) as u8);
    out.push(v as u8);
}

struct SCT<'a> {
    log_id: &'a [u8],
    timestamp: u64,
    sig_alg: u16,
    sig: &'a [u8],
    exts: &'a [u8],
}

const ECDSA_SHA256: u16 = 0x0403;
const ECDSA_SHA384: u16 = 0x0503;
const RSA_PKCS1_SHA256: u16 = 0x0401;
const RSA_PKCS1_SHA384: u16 = 0x0501;
const SCT_V1: u8 = 0u8;
const SCT_TIMESTAMP: u8 = 0u8;
const SCT_X509_ENTRY: [u8; 2] = [0, 0];

impl<'a> SCT<'a> {
    fn verify(&self, key: &[u8], cert: &[u8]) -> Result<(), Error> {
        let alg: &dyn ring::signature::VerificationAlgorithm = match self.sig_alg {
            ECDSA_SHA256 => &ring::signature::ECDSA_P256_SHA256_ASN1,
            ECDSA_SHA384 => &ring::signature::ECDSA_P384_SHA384_ASN1,
            RSA_PKCS1_SHA256 => &ring::signature::RSA_PKCS1_2048_8192_SHA256,
            RSA_PKCS1_SHA384 => &ring::signature::RSA_PKCS1_2048_8192_SHA384,
            _ => return Err(Error::InvalidSignature)
        };

        let mut data = Vec::new();
        data.push(SCT_V1);
        data.push(SCT_TIMESTAMP);
        write_u64(self.timestamp, &mut data);
        data.extend_from_slice(&SCT_X509_ENTRY);
        write_u24(cert.len() as u32, &mut data);
        data.extend_from_slice(cert);
        write_u16(self.exts.len() as u16, &mut data);
        data.extend_from_slice(self.exts);

        let key = ring::signature::UnparsedPublicKey::new(alg, key);

        key.verify(&data, self.sig)
            .map_err(|_| Error::InvalidSignature)
    }

    fn parse(enc: &'a [u8]) -> Result<SCT<'a>, Error> {
        let inp = untrusted::Input::from(enc);

        inp.read_all(
            Error::MalformedSCT,
            |rd| {
                let version = rd.read_byte()
                    .map_err(|_| Error::MalformedSCT)?;
                if version != 0 {
                    return Err(Error::UnsupportedSCTVersion);
                }

                let id = rd.read_bytes(32)
                    .map_err(|_| Error::MalformedSCT)?;
                let timestamp = rd.read_bytes(8)
                    .map_err(|_| Error::MalformedSCT)
                    .map(decode_u64)?;

                let ext_len = rd.read_bytes(2)
                    .map_err(|_| Error::MalformedSCT)
                    .map(decode_u16)?;
                let exts = rd.read_bytes(ext_len as usize)
                    .map_err(|_| Error::MalformedSCT)?;

                let sig_alg = rd.read_bytes(2)
                    .map_err(|_| Error::MalformedSCT)
                    .map(decode_u16)?;
                let sig_len = rd.read_bytes(2)
                    .map_err(|_| Error::MalformedSCT)
                    .map(decode_u16)?;
                let sig = rd.read_bytes(sig_len as usize)
                    .map_err(|_| Error::MalformedSCT)?;

                let ret = SCT {
                    log_id: id.as_slice_less_safe(),
                    timestamp: timestamp,
                    sig_alg: sig_alg,
                    sig: sig.as_slice_less_safe(),
                    exts: exts.as_slice_less_safe(),
                };

                Ok(ret)
            })
    }
}

/// Verifies that the SCT `sct` (a `SignedCertificateTimestamp` encoding)
/// is a correctly signed timestamp for `cert` (a DER-encoded X.509 end-entity
/// certificate) valid `at_time`.  `logs` describe the CT logs trusted by
/// the caller to sign such an SCT.
///
/// On success, this function returns the log used as an index into `logs`.
/// Otherwise, it returns an `Error`.
pub fn verify_sct(cert: &[u8],
                  sct: &[u8],
                  at_time: u64,
                  logs: &[&Log]) -> Result<usize, Error> {
    let sct = SCT::parse(sct)?;
    let i = lookup(logs, &sct.log_id)?;
    let log = logs[i];
    sct.verify(log.key, cert)?;

    if sct.timestamp > at_time {
        return Err(Error::TimestampInFuture);
    }

    Ok(i)
}

#[cfg(test)]
mod tests_google;
#[cfg(test)]
mod tests_generated;
#[cfg(test)]
mod tests;