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use alloc::vec;
use alloc::vec::Vec;
use digest::DynDigest;
use rand::{Rng, RngCore};
use subtle::ConstantTimeEq;
use crate::algorithms::mgf1_xor;
use crate::errors::{Error, Result};
use crate::key::{PrivateKey, PublicKey};
pub fn verify<PK: PublicKey>(
pub_key: &PK,
hashed: &[u8],
sig: &[u8],
digest: &mut dyn DynDigest,
) -> Result<()> {
if sig.len() != pub_key.size() {
return Err(Error::Verification);
}
let em_bits = pub_key.n().bits() - 1;
let em_len = (em_bits + 7) / 8;
let mut em = pub_key.raw_encryption_primitive(sig, em_len)?;
emsa_pss_verify(hashed, &mut em, em_bits, None, digest)
}
pub fn sign<T: RngCore + ?Sized, S: Rng, SK: PrivateKey>(
rng: &mut T,
blind_rng: Option<&mut S>,
priv_key: &SK,
hashed: &[u8],
salt_len: Option<usize>,
digest: &mut dyn DynDigest,
) -> Result<Vec<u8>> {
let salt_len = salt_len.unwrap_or_else(|| priv_key.size() - 2 - digest.output_size());
let mut salt = vec![0; salt_len];
rng.fill(&mut salt[..]);
sign_pss_with_salt(blind_rng, priv_key, hashed, &salt, digest)
}
fn sign_pss_with_salt<T: Rng, SK: PrivateKey>(
blind_rng: Option<&mut T>,
priv_key: &SK,
hashed: &[u8],
salt: &[u8],
digest: &mut dyn DynDigest,
) -> Result<Vec<u8>> {
let em_bits = priv_key.n().bits() - 1;
let em = emsa_pss_encode(hashed, em_bits, salt, digest)?;
priv_key.raw_decryption_primitive(blind_rng, &em, priv_key.size())
}
fn emsa_pss_encode(
m_hash: &[u8],
em_bits: usize,
salt: &[u8],
hash: &mut dyn DynDigest,
) -> Result<Vec<u8>> {
let h_len = hash.output_size();
let s_len = salt.len();
let em_len = (em_bits + 7) / 8;
if m_hash.len() != h_len {
return Err(Error::InputNotHashed);
}
if em_len < h_len + s_len + 2 {
return Err(Error::Internal);
}
let mut em = vec![0; em_len];
let (db, h) = em.split_at_mut(em_len - h_len - 1);
let h = &mut h[..(em_len - 1) - db.len()];
let prefix = [0u8; 8];
hash.update(&prefix);
hash.update(m_hash);
hash.update(salt);
let hashed = hash.finalize_reset();
h.copy_from_slice(&hashed);
db[em_len - s_len - h_len - 2] = 0x01;
db[em_len - s_len - h_len - 1..].copy_from_slice(salt);
mgf1_xor(db, hash, &h);
db[0] &= 0xFF >> (8 * em_len - em_bits);
em[em_len - 1] = 0xBC;
Ok(em)
}
fn emsa_pss_verify(
m_hash: &[u8],
em: &mut [u8],
em_bits: usize,
s_len: Option<usize>,
hash: &mut dyn DynDigest,
) -> Result<()> {
let h_len = hash.output_size();
if m_hash.len() != h_len {
return Err(Error::Verification);
}
let em_len = em.len();
if em_len < h_len + s_len.unwrap_or_default() + 2 {
return Err(Error::Verification);
}
if em[em.len() - 1] != 0xBC {
return Err(Error::Verification);
}
let (db, h) = em.split_at_mut(em_len - h_len - 1);
let h = &mut h[..h_len];
if db[0] & (0xFF << (8 - (8 * em_len - em_bits))) != 0 {
return Err(Error::Verification);
}
mgf1_xor(db, hash, &*h);
db[0] &= 0xFF >> (8 * em_len - em_bits);
let s_len = match s_len {
None => (0..=em_len - (h_len + 2))
.rev()
.try_fold(None, |state, i| match (state, db[em_len - h_len - i - 2]) {
(Some(i), _) => Ok(Some(i)),
(_, 1) => Ok(Some(i)),
(_, 0) => Ok(None),
_ => Err(Error::Verification),
})?
.ok_or(Error::Verification)?,
Some(s_len) => {
let (zeroes, rest) = db.split_at(em_len - h_len - s_len - 2);
if zeroes.iter().any(|e| *e != 0x00) || rest[0] != 0x01 {
return Err(Error::Verification);
}
s_len
}
};
let salt = &db[db.len() - s_len..];
let prefix = [0u8; 8];
hash.update(&prefix[..]);
hash.update(m_hash);
hash.update(salt);
let h0 = hash.finalize_reset();
if h0.ct_eq(h).into() {
Ok(())
} else {
Err(Error::Verification)
}
}
#[cfg(test)]
mod test {
use crate::{PaddingScheme, PublicKey, RsaPrivateKey, RsaPublicKey};
use num_bigint::BigUint;
use num_traits::{FromPrimitive, Num};
use rand::{rngs::StdRng, SeedableRng};
use sha1::{Digest, Sha1};
use std::time::SystemTime;
fn get_private_key() -> RsaPrivateKey {
RsaPrivateKey::from_components(
BigUint::from_str_radix("9353930466774385905609975137998169297361893554149986716853295022578535724979677252958524466350471210367835187480748268864277464700638583474144061408845077", 10).unwrap(),
BigUint::from_u64(65537).unwrap(),
BigUint::from_str_radix("7266398431328116344057699379749222532279343923819063639497049039389899328538543087657733766554155839834519529439851673014800261285757759040931985506583861", 10).unwrap(),
vec![
BigUint::from_str_radix("98920366548084643601728869055592650835572950932266967461790948584315647051443",10).unwrap(),
BigUint::from_str_radix("94560208308847015747498523884063394671606671904944666360068158221458669711639", 10).unwrap()
],
)
}
#[test]
fn test_verify_pss() {
let priv_key = get_private_key();
let tests = [[
"test\n", "6f86f26b14372b2279f79fb6807c49889835c204f71e38249b4c5601462da8ae30f26ffdd9c13f1c75eee172bebe7b7c89f2f1526c722833b9737d6c172a962f"
]];
let pub_key: RsaPublicKey = priv_key.into();
for test in &tests {
let digest = Sha1::digest(test[0].as_bytes()).to_vec();
let sig = hex::decode(test[1]).unwrap();
let seed = SystemTime::now()
.duration_since(SystemTime::UNIX_EPOCH)
.unwrap();
let rng = StdRng::seed_from_u64(seed.as_secs());
pub_key
.verify(PaddingScheme::new_pss::<Sha1, _>(rng), &digest, &sig)
.expect("failed to verify");
}
}
#[test]
fn test_sign_and_verify_roundtrip() {
let priv_key = get_private_key();
let tests = ["test\n"];
let seed = SystemTime::now()
.duration_since(SystemTime::UNIX_EPOCH)
.unwrap();
let rng = StdRng::seed_from_u64(seed.as_secs());
for test in &tests {
let digest = Sha1::digest(test.as_bytes()).to_vec();
let sig = priv_key
.sign_blinded(
&mut rng.clone(),
PaddingScheme::new_pss::<Sha1, _>(rng.clone()),
&digest,
)
.expect("failed to sign");
priv_key
.verify(
PaddingScheme::new_pss::<Sha1, _>(rng.clone()),
&digest,
&sig,
)
.expect("failed to verify");
}
}
}