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|
//! PublicKey-Encrypted Session Key packets.
//!
//! 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
#[cfg(test)]
use quickcheck::{Arbitrary, Gen};
use crate::Error;
use crate::packet::key;
use crate::packet::Key;
use crate::KeyID;
use crate::crypto::Decryptor;
use crate::crypto::mpi::Ciphertext;
use crate::Packet;
use crate::PublicKeyAlgorithm;
use crate::Result;
use crate::SymmetricAlgorithm;
use crate::crypto::SessionKey;
use crate::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
// IMPORTANT: If you add fields to this struct, you need to explicitly
// IMPORTANT: implement PartialEq, Eq, and Hash.
#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct PKESK3 {
/// CTB header fields.
pub(crate) common: packet::Common,
/// Key ID of the key this is encrypted to.
recipient: KeyID,
/// Public key algorithm used to encrypt the session key.
pk_algo: PublicKeyAlgorithm,
/// The encrypted session key.
esk: Ciphertext,
}
assert_send_and_sync!(PKESK3);
impl PKESK3 {
/// Creates a new PKESK3 packet.
pub fn new(recipient: KeyID, pk_algo: PublicKeyAlgorithm,
encrypted_session_key: Ciphertext)
-> Result<PKESK3> {
Ok(PKESK3 {
common: Default::default(),
recipient,
pk_algo,
esk: encrypted_session_key,
})
}
/// Creates a new PKESK3 packet for the given recipent.
///
/// The given symmetric algorithm must match the algorithm that is
/// used to encrypt the payload.
pub fn for_recipient<P, R>(algo: SymmetricAlgorithm,
session_key: &SessionKey,
recipient: &Key<P, R>)
-> Result<PKESK3>
where P: key::KeyParts,
R: key::KeyRole,
{
// 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, i.e. as u16.
let checksum = session_key
.iter()
.cloned()
.map(u16::from)
.fold(0u16, u16::wrapping_add);
psk.extend_from_slice(&checksum.to_be_bytes());
let psk: SessionKey = psk.into();
let esk = recipient.encrypt(&psk)?;
Ok(PKESK3{
common: Default::default(),
recipient: recipient.keyid(),
pk_algo: recipient.pk_algo(),
esk,
})
}
/// Gets the recipient.
pub fn recipient(&self) -> &KeyID {
&self.recipient
}
/// Sets the recipient.
pub fn set_recipient(&mut self, recipient: KeyID) -> KeyID {
::std::mem::replace(&mut 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) -> PublicKeyAlgorithm {
::std::mem::replace(&mut 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) -> Ciphertext {
::std::mem::replace(&mut self.esk, esk)
}
/// Decrypts the encrypted session key.
///
/// If the symmetric algorithm used to encrypt the message is
/// known in advance, it should be given as argument. This allows
/// us to reduce the side-channel leakage of the decryption
/// operation for RSA.
///
/// Returns the session key and symmetric algorithm used to
/// encrypt the following payload.
///
/// Returns `None` on errors. This prevents leaking information
/// to an attacker, which could lead to compromise of secret key
/// material with certain algorithms (RSA). See [Section 14 of
/// RFC 4880].
///
/// [Section 14 of RFC 4880]: https://tools.ietf.org/html/rfc4880#section-14
pub fn decrypt(&self, decryptor: &mut dyn Decryptor,
sym_algo_hint: Option<SymmetricAlgorithm>)
-> Option<(SymmetricAlgorithm, SessionKey)>
{
self.decrypt_insecure(decryptor, sym_algo_hint).ok()
}
fn decrypt_insecure(&self, decryptor: &mut dyn Decryptor,
sym_algo_hint: Option<SymmetricAlgorithm>)
-> Result<(SymmetricAlgorithm, SessionKey)>
{
let plaintext_len = if let Some(s) = sym_algo_hint {
Some(1 /* cipher octet */ + s.key_size()? + 2 /* chksum */)
} else {
None
};
let plain = decryptor.decrypt(&self.esk, plaintext_len)?;
let key_rgn = 1..(plain.len() - 2);
let sym_algo: SymmetricAlgorithm = plain[0].into();
let mut key: SessionKey = vec![0u8; sym_algo.key_size()?].into();
if key_rgn.len() != sym_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
|