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@phochard
phochard committed Nov 20, 2024
1 parent 3c4ffa2 commit 2d6fa6d
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Showing 4 changed files with 45 additions and 61 deletions.
17 changes: 11 additions & 6 deletions src/api.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,9 +9,13 @@ use super::{
traits::AE,
};
use crate::{
abe_policy::{AccessPolicy, Right}, core::{
primitives::{decaps, encaps, full_decaps, refresh, rekey, setup}, MasterPublicKey, MasterSecretKey, UserSecretKey, XEnc, SHARED_SECRET_LENGTH
}, traits::{KemAc, PkeAc}, Error
abe_policy::{AccessPolicy, Right},
core::{
primitives::{decaps, encaps, full_decaps, refresh, rekey, setup},
MasterPublicKey, MasterSecretKey, UserSecretKey, XEnc, SHARED_SECRET_LENGTH,
},
traits::{KemAc, PkeAc},
Error,
};

#[derive(Debug)]
Expand Down Expand Up @@ -142,6 +146,7 @@ impl KemAc<SHARED_SECRET_LENGTH> for Covercrypt {
type EncapsulationKey = MasterPublicKey;
type DecapsulationKey = UserSecretKey;
type Encapsulation = XEnc;
type FullDecapsulationKey = MasterSecretKey;
type Error = Error;

fn encaps(
Expand All @@ -166,10 +171,10 @@ impl KemAc<SHARED_SECRET_LENGTH> for Covercrypt {

fn full_decaps(
&self,
usk: &UserSecretKey,
msk: &MasterSecretKey,
enc: &XEnc,
) -> Result<Option<Vec<(Right, Secret<SHARED_SECRET_LENGTH>)>>, Error>{
full_decaps(usk, enc)
) -> Result<Vec<(Right, Secret<SHARED_SECRET_LENGTH>)>, Error> {
full_decaps( enc, msk)
}
}

Expand Down
81 changes: 29 additions & 52 deletions src/core/primitives.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ use std::{
use cosmian_crypto_core::{
bytes_ser_de::Serializable,
reexport::rand_core::{CryptoRngCore, RngCore},
RandomFixedSizeCBytes, Secret, SymmetricKey,
R25519CurvePoint, RandomFixedSizeCBytes, Secret, SymmetricKey,
};

use tiny_keccak::{Hasher, IntoXof, Kmac, Shake, Xof};
Expand Down Expand Up @@ -268,24 +268,7 @@ pub fn decaps(
for enc in &encapsulation.encapsulations {
// The breadth-first search tries all coordinate subkeys in a chronological order.
for key in usk.secrets.bfs() {
let S = match (key, enc) {
(RightSecretKey::Hybridized { sk, dk }, Encapsulation::Hybridized { E, F }) => {
let mut K1 = h_hash(R25519::session_key(sk, &A)?);
let K2 = MlKem512::dec(dk, E)?;
let S = xor_3(F, &K1, &K2);
K1.zeroize();
S
}
(RightSecretKey::Classic { sk }, Encapsulation::Classic { F }) => {
let K1 = h_hash(R25519::session_key(sk, &A)?);
xor_2(F, &K1)
}
(RightSecretKey::Hybridized { .. }, Encapsulation::Classic { .. })
| (RightSecretKey::Classic { .. }, Encapsulation::Hybridized { .. }) => {
continue;
}
};

let S = S(key, enc, A.clone());
let (tag, ss) = j_hash(&S, &encapsulation.c, &encapsulation.encapsulations)?;

if tag == encapsulation.tag {
Expand Down Expand Up @@ -455,48 +438,42 @@ fn refresh_coordinate_keys(
/// Attempts opening the Covercrypt encapsulation using the given USK. Returns
/// the encapsulated key and associated rights upon success, otherwise returns `None`.
pub fn full_decaps(
usk: &UserSecretKey,
encapsulation: &XEnc,
) -> Result<Option<Vec<(Right, Secret<SHARED_SECRET_LENGTH>)>>, Error> {
msk: &MasterSecretKey,
) -> Result<Vec<(Right, Secret<SHARED_SECRET_LENGTH>)>, Error> {
// A = ⊙ _i (α_i. c_i)
let A = usk
.id
.iter()
.zip(encapsulation.c.iter())
.map(|(marker, trap)| trap * marker)
.fold(EcPoint::identity(), |mut acc, elt| {
acc = &acc + &elt;
acc
});
let A = msk.tsk.binding_point();

let mut rights_list: Vec<(Right, Secret<SHARED_SECRET_LENGTH>)> = Vec::new();

for enc in &encapsulation.encapsulations {
let mut rights_list: Vec<(Right, Secret<SHARED_SECRET_LENGTH>)> = Vec::new();
for secret in usk.secrets.flat_iter() {
let S = match (secret.1, enc) {
(RightSecretKey::Hybridized { sk, dk }, Encapsulation::Hybridized { E, F }) => {
let mut K1 = h_hash(R25519::session_key(&sk, &A)?);
let K2 = MlKem512::dec(&dk, E)?;
let S = xor_3(F, &K1, &K2);
K1.zeroize();
S
}
(RightSecretKey::Classic { sk }, Encapsulation::Classic { F }) => {
let K1 = h_hash(R25519::session_key(&sk, &A)?);
xor_2(F, &K1)
}
(RightSecretKey::Hybridized { .. }, Encapsulation::Classic { .. })
| (RightSecretKey::Classic { .. }, Encapsulation::Hybridized { .. }) => {
continue;
}
};
for (right,mut key) in msk.secrets.iter() {

let S = S(key, enc, A.clone());
let (tag, ss) = j_hash(&S, &encapsulation.c, &encapsulation.encapsulations)?;

if tag == encapsulation.tag {
rights_list.push((secret.0.clone(), ss));
rights_list.push((right.clone(), ss));
}
}
return Ok(Some(rights_list));
}
Ok(None)
Ok(rights_list)
}

fn S(key: &RightSecretKey, enc: &Encapsulation, A: R25519CurvePoint) -> [u8; 32] {
return match (key, enc) {
(RightSecretKey::Hybridized { sk, dk }, Encapsulation::Hybridized { E, F }) => {
let mut K1 = h_hash(R25519::session_key(&sk, &A).unwrap());
let K2 = MlKem512::dec(&dk, &E).unwrap();
let S = xor_3(&F, &K1, &K2);
K1.zeroize();
S
}
(RightSecretKey::Classic { sk }, Encapsulation::Classic { F }) => {
let K1 = h_hash(R25519::session_key(&sk, &A).unwrap());
xor_2(&F, &K1)
}
(RightSecretKey::Hybridized { .. }, Encapsulation::Classic { .. })
| (RightSecretKey::Classic { .. }, Encapsulation::Hybridized { .. }) => todo! {},
};
}
3 changes: 2 additions & 1 deletion src/core/tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -261,7 +261,8 @@ fn test_covercrypt_kem() {
let (secret, enc) = cc.encaps(&mpk, &ap).unwrap();
let res = cc.decaps(&usk, &enc).unwrap();
assert_eq!(secret, res.unwrap());
let full = cc.full_decaps(&usk, &enc).unwrap().unwrap();
let full = cc.full_decaps(&msk, &enc).unwrap();
println!("{:?}", full);
assert_eq!(full[0].1, secret);
}

Expand Down
5 changes: 3 additions & 2 deletions src/traits.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ pub trait KemAc<const LENGTH: usize> {
type EncapsulationKey;
type DecapsulationKey;
type Encapsulation;
type FullDecapsulationKey;
type Error: std::error::Error;

/// Generates a new encapsulation for the given access policy.
Expand All @@ -33,9 +34,9 @@ pub trait KemAc<const LENGTH: usize> {

fn full_decaps(
&self,
dk: &Self::DecapsulationKey,
fdk: &Self::FullDecapsulationKey,
enc: &Self::Encapsulation,
) -> Result<Option<Vec<(Right, Secret<LENGTH>)>>, Self::Error>;
) -> Result<Vec<(Right, Secret<LENGTH>)>, Self::Error>;
}

pub trait AE<const KEY_LENGTH: usize> {
Expand Down

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