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|
//! String-to-Key (S2K) specifiers.
//!
//! String-to-key (S2K) specifiers are used to convert password
//! strings into symmetric-key encryption/decryption keys. See
//! [Section 3.7 of RFC 4880].
//!
//! [Section 3.7 of RFC 4880]: https://tools.ietf.org/html/rfc4880#section-3.7
use Error;
use Result;
use HashAlgorithm;
use crypto::Password;
use crypto::SessionKey;
use std::fmt;
use nettle::{Hash, Yarrow, Random};
use quickcheck::{Arbitrary, Gen};
use rand::Rng;
/// String-to-Key (S2K) specifiers.
///
/// String-to-key (S2K) specifiers are used to convert password
/// strings into symmetric-key encryption/decryption keys. See
/// [Section 3.7 of RFC 4880].
///
/// [Section 3.7 of RFC 4880]: https://tools.ietf.org/html/rfc4880#section-3.7
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
pub enum S2K {
/// Simply hashes the password.
Simple {
/// Hash used for key derivation.
hash: HashAlgorithm
},
/// Hashes the password with a public `salt` value.
Salted {
/// Hash used for key derivation.
hash: HashAlgorithm,
/// Public salt value mixed into the password.
salt: [u8; 8],
},
/// Repeatently hashes the password with a public `salt` value.
Iterated {
/// Hash used for key derivation.
hash: HashAlgorithm,
/// Public salt value mixed into the password.
salt: [u8; 8],
/// Number of bytes to hash.
iterations: u32,
},
/// Private S2K algorithm
Private(u8),
/// Unknown S2K algorithm
Unknown(u8),
}
// XXX: Check defaults.
impl Default for S2K {
fn default() -> Self {
let mut salt = [0u8; 8];
Yarrow::default().random(&mut salt);
S2K::Iterated {
hash: HashAlgorithm::SHA256,
salt: salt,
iterations: 26214400, // XXX: Calibrate somehow.
}
}
}
impl S2K {
/// Convert the string to a key using the S2K's paramters.
pub fn derive_key(&self, string: &Password, key_size: usize)
-> Result<SessionKey> {
match self {
&S2K::Simple { hash } | &S2K::Salted { hash, .. }
| &S2K::Iterated { hash, .. } => {
let mut hash = hash.context()?;
// If the digest length is shorter than the key length,
// then we need to concatenate multiple hashes, each
// preloaded with i 0s.
let hash_sz = hash.digest_size();
let num_contexts = (key_size + hash_sz - 1) / hash_sz;
let mut zeros = Vec::with_capacity(num_contexts + 1);
let mut ret = vec![0u8; key_size];
for data in ret.chunks_mut(hash_sz) {
hash.update(&zeros[..]);
match self {
&S2K::Simple { .. } => {
hash.update(string);
}
&S2K::Salted { ref salt, .. } => {
hash.update(salt);
hash.update(string);
}
&S2K::Iterated { ref salt, iterations, .. } => {
// Independent of what the iteration count is, we
// always hash the whole salt and password once.
// The iteration value counts the _bytes_ to be
// hashed.
let octs_per_iter = salt.len() + string.len();
let mut data = vec![0u8; octs_per_iter];
let full = iterations as usize / octs_per_iter;
let tail = iterations as usize - (full * octs_per_iter);
data[0..salt.len()].clone_from_slice(salt);
data[salt.len()..].clone_from_slice(string);
for _ in 0..full {
hash.update(&data);
}
if tail != 0 {
hash.update(&data[0..tail]);
}
}
&S2K::Unknown(_) | &S2K::Private(_) => unreachable!(),
}
hash.digest(data);
zeros.push(0);
}
Ok(ret.into())
}
&S2K::Unknown(u) | &S2K::Private(u) =>
Err(Error::MalformedPacket(
format!("Unknown S2K type {:#x}", u)).into()),
}
}
/// Not all iteration counts are encodable as Iterated and Salted S2K. This function returns
/// an encodabled iteration count larger or equal `iters`.
/// # Note
/// The largest encodable iteration count is 0x3e00000.
pub fn nearest_iteration_count(iters: usize) -> u32 {
use std::usize;
match iters {
0...1024 => 1024,
1025...2048 => iters as u32,
0x3e00001...usize::MAX => 0x3e00000,
iters => {
let iters = iters as u32;
let msb = 32 - iters.leading_zeros();
let mantissa_mask = 0b1111_000000 << (msb - 11);
let tail_mask = (1 << (msb - 11)) - 1;
let mantissa = (iters & mantissa_mask) >> (msb - 5);
let exp = if msb < 11 { 0 } else { msb - 11 };
if iters & tail_mask != 0 {
if mantissa < 0b1111 {
Self::decode_count((mantissa as u8 + 1) | exp as u8)
} else {
Self::decode_count(
|