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
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
use Error;
use packet::Key;
use KeyID;
use crypto::mpis::{self, MPI, Ciphertext};
use Packet;
use PublicKeyAlgorithm;
use Result;
use SymmetricAlgorithm;
use crypto::SessionKey;
use crypto::ecdh;
use nettle::{rsa, Yarrow};
use packet;

/// Holds an asymmetrically encrypted session key.
///
/// The session key is needed to decrypt the actual ciphertext.  See
/// [Section 5.1 of RFC 4880] for details.
///
///   [Section 5.1 of RFC 4880]: https://tools.ietf.org/html/rfc4880#section-5.1
#[derive(PartialEq, Eq, Hash, Clone, Debug)]
pub struct PKESK {
    /// CTB header fields.
    pub(crate) common: packet::Common,
    /// Packet version. Must be 3.
    pub(crate) version: u8,
    /// Key ID of the key this is encrypted to.
    pub(crate) recipient: KeyID,
    /// Public key algorithm used to encrypt the session key.
    pub(crate) pk_algo: PublicKeyAlgorithm,
    /// The encrypted session key.
    pub(crate) esk: Ciphertext,
}

impl PKESK {
    /// Creates a new PKESK packet.
    ///
    /// The given symmetric algorithm must match the algorithm that is
    /// used to encrypt the payload.
    pub fn new(algo: SymmetricAlgorithm,
               session_key: &SessionKey, recipient: &Key)
               -> Result<PKESK> {
        use PublicKeyAlgorithm::*;
        let mut rng = Yarrow::default();

        // We need to prefix the cipher specifier to the session key,
        // and a two-octet checksum.
        let mut psk = Vec::with_capacity(1 + session_key.len() + 2);
        psk.push(algo.into());
        psk.extend_from_slice(session_key);

        // Compute the sum modulo 65536.
        let checksum
            = session_key.iter().map(|&x| x as usize).sum::<usize>() & 0xffff;
        psk.push((checksum >> 8) as u8);
        psk.push((checksum >> 0) as u8);

        #[allow(deprecated)]
        let esk = match recipient.pk_algo {
            RSAEncryptSign | RSAEncrypt => {
                // Extract the public recipient.
                match recipient.mpis() {
                    &mpis::PublicKey::RSA { ref e, ref n } => {
                        // The ciphertext has the length of the modulus.
                        let mut esk = vec![0u8; n.value.len()];

                        let pk = rsa::PublicKey::new(&n.value, &e.value)?;
                        rsa::encrypt_pkcs1(&pk, &mut rng, &psk, &mut esk)?;
                        Ciphertext::RSA {c: MPI::new(&esk)}
                    }

                    pk => {
                        return Err(
                            Error::MalformedPacket(
                                format!(
                                    "Key: Expected RSA public key, got {:?}",
                                    pk)).into());
                    }
                }
            },

            ECDH => {
                ecdh::wrap_session_key(recipient, &psk)?
            }
            algo =>
                return Err(Error::UnsupportedPublicKeyAlgorithm(algo).into()),
        };

        Ok(PKESK{
            common: Default::default(),
            version: 3,
            recipient: recipient.keyid(),
            pk_algo: recipient.pk_algo,
            esk: esk,
        })
    }

    /// Gets the version.
    pub fn version(&self) -> u8 {
        self.version
    }

    /// Gets the recipient.
    pub fn recipient(&self) -> &KeyID {
        &self.recipient
    }

    /// Sets the recipient.
    pub fn set_recipient(&mut self, recipient: KeyID) {
        self.recipient = recipient;
    }

    /// Gets the public key algorithm.
    pub fn pk_algo(&self) -> PublicKeyAlgorithm {
        self.pk_algo
    }

    /// Sets the public key algorithm.
    pub fn set_pk_algo(&mut self, algo: PublicKeyAlgorithm) {
        self.pk_algo = algo;
    }

    /// Gets the encrypted session key.
    pub fn esk(&self) -> &Ciphertext {
        &self.esk
    }

    /// Sets the encrypted session key.
    pub fn set_esk(&mut self, esk: Ciphertext) {
        self.esk = esk;
    }

    /// Decrypts the ESK and returns the session key and symmetric algorithm
    /// used to encrypt the following payload.
    pub fn decrypt(&self, recipient: &Key, recipient_sec: &mpis::SecretKey)
        -> Result<(SymmetricAlgorithm, SessionKey)>
    {
        use PublicKeyAlgorithm::*;
        use crypto::mpis::PublicKey;
        use nettle::rsa;

        let plain: SessionKey = match
            (self.pk_algo, recipient.mpis(), recipient_sec, &self.esk)
        {
            (RSAEncryptSign,
             &PublicKey::RSA{ ref e, ref n },
             &mpis::SecretKey::RSA{ ref p, ref q, ref d, .. },
             &mpis::Ciphertext::RSA{ ref c }) => {
                let public = rsa::PublicKey::new(&n.value, &e.value)?;
                let secret = rsa::PrivateKey::new(&d.value, &p.value,
                                                  &q.value, Option::None)?;
                let mut rand = Yarrow::default();
                rsa::decrypt_pkcs1(&public, &secret, &mut rand, &c.value)?
            }

            (ElgamalEncrypt,
             &PublicKey::Elgamal{ .. },
             &mpis::SecretKey::Elgamal{ .. },
             &mpis::Ciphertext::Elgamal{ .. }) =>
                return Err(
                    Error::UnsupportedPublicKeyAlgorithm(self.pk_algo).into()),

            (ECDH,
             PublicKey::ECDH{ .. },
             mpis::SecretKey::ECDH { .. },
             mpis::Ciphertext::ECDH { .. }) =>
                ecdh::unwrap_session_key(recipient, recipient_sec, &self.esk)?,

            (algo, public, secret, cipher) =>
                return Err(Error::MalformedPacket(format!(
                    "unsupported combination of algorithm {:?}, key pair {:?}/{:?} and ciphertext {:?}",
                    algo, public, secret, cipher)).into()),
        }.into();

        let key_rgn = 1..(plain.len() - 2);
        let symm_algo: SymmetricAlgorithm = plain[0].into();
        let mut key = vec![0u8; symm_algo.key_size()?];

        if key_rgn.len() != symm_algo.key_size()? {
            return Err(Error::MalformedPacket(
                format!("session key has the wrong size")).into());
        }

        key.copy_from_slice(&plain[key_rgn]);

        let our_checksum
            = key.iter().map(|&x| x as usize).sum::<usize>() & 0xffff;
        let their_checksum = (plain[plain.len() - 2] as usize) << 8
            | (plain[plain.len() - 1] as usize);

        if their_checksum == our_checksum {
            Ok((symm_algo, key.into()))
        } else {
            Err(Error::MalformedPacket(format!("key checksum wrong"))
                .into())
        }
    }

    /// Convert the `PKESK` struct to a `Packet`.
    pub fn to_packet(self) -> Packet {
        Packet::PKESK(self)
    }
}

impl From<PKESK> for Packet {
    fn from(s: PKESK) -> Self {
        s.to_packet()
    }
}

#[cfg(test)]
mod tests {
    use TPK;
    use PacketPile;
    use SecretKey;
    use Packet;
    use std::path::PathBuf;

    fn path_to_key(artifact: &str) -> PathBuf {
        [env!("CARGO_MANIFEST_DIR"), "tests", "data", "keys", artifact]
            .iter().collect()
    }

    fn path_to_msg(artifact: &str) -> PathBuf {
        [env!("CARGO_MANIFEST_DIR"), "tests", "data", "messages", artifact]
            .iter().collect()
    }

    #[test]
    fn decrypt_rsa() {
        let tpk = TPK::from_file(
            path_to_key("testy-private.pgp")).unwrap();
        let pile = PacketPile::from_file(
            path_to_msg("encrypted-to-testy.gpg")).unwrap();
        let pair = tpk.subkeys().next().unwrap().subkey();

        if let Some(SecretKey::Unencrypted{ mpis: ref sec }) = pair.secret {
            let pkg = pile.descendants().skip(0).next().clone();

            if let Some(Packet::PKESK(ref pkesk)) = pkg {
                let plain = pkesk.decrypt(&pair, sec).unwrap();

                eprintln!("plain: {:?}", plain);
            } else {
                panic!("message is not a PKESK packet");
            }
        } else {
            panic!("secret key is encrypted/missing");
        }
    }

    #[test]
    fn decrypt_ecdh_cv25519() {
        let tpk = TPK::from_file(
            path_to_key("testy-new-private.pgp")).unwrap();
        let pile = PacketPile::from_file(
            path_to_msg("encrypted-to-testy-new.pgp")).unwrap();
        let pair = tpk.subkeys().next().unwrap().subkey();

        if let Some(SecretKey::Unencrypted{ mpis: ref sec }) = pair.secret {
            let pkg = pile.descendants().skip(0).next().clone();

            if let Some(Packet::PKESK(ref pkesk)) = pkg {
                let plain = pkesk.decrypt(&pair, sec).unwrap();

                eprintln!("plain: {:?}", plain);
            } else {
                panic!("message is not a PKESK packet");
            }
        } else {
            panic!("secret key is encrypted/missing");
        }
    }

    #[test]
    fn decrypt_with_short_cv25519_secret_key() {
        use conversions::Time;
        use super::PKESK;
        use crypto::SessionKey;
        use crypto::mpis::{self, MPI};
        use PublicKeyAlgorithm;
        use SymmetricAlgorithm;
        use HashAlgorithm;
        use constants::Curve;
        use packet::Key;
        use nettle::{curve25519, Yarrow};
        use time;

        // 20 byte sec key
        let mut sec = [
            0x0,0x0,
            0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,
            0x1,0x2,0x2,0x2,0x2,0x2,0x2,0x2,0x2,0x2,
            0x1,0x2,0x2,0x2,0x2,0x2,0x2,0x2,0x0,0x0
        ];
        let mut pnt = [0x40u8; curve25519::CURVE25519_SIZE + 1];
        curve25519::mul_g(&mut pnt[1..], &sec[..]).unwrap();
        sec.reverse();

        let public_mpis = mpis::PublicKey::ECDH {
            curve: Curve::Cv25519,
            q: MPI::new(&pnt[..]),
            hash: HashAlgorithm::SHA256,
            sym: SymmetricAlgorithm::AES256,
        };
        let private_mpis = mpis::SecretKey::ECDH {
            scalar: MPI::new(&sec[..]),
        };
        let key = Key{
            common: Default::default(),
            version: 4,
            creation_time: time::now().canonicalize(),
            pk_algo: PublicKeyAlgorithm::ECDH,
            mpis: public_mpis,
            secret: None,
        };
        let mut rng = Yarrow::default();
        let sess_key = SessionKey::new(&mut rng, 32);
        let pkesk = PKESK::new(SymmetricAlgorithm::AES256, &sess_key, &key).unwrap();

        pkesk.decrypt(&key, &private_mpis).unwrap();
    }
}