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Unify mechanism traits
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This patch combines the operation traits that were previously used to
call mechanism implementations into a single MechanismImpl trait.  This
has several advantages:
- We can use a macro to implement the dispatch from the Mechanism enum,
  removing boilerplate code from the reply_to implementation.
- To implement an operation for a mechanism, it is now sufficient to
  override the respective trait method.  It is no longer necessary to
  also update reply_to.
- The need to annotate all mechanism methods with #[inline(never)] to
  avoid producing a huge reply_to function (see the comment in
  mechanisms.rs) is reduced as we can just mark the methods generated by
  the macro as #[inline(never)].
- This reduces the binary size required in the stable
  nitrokey-3-firmware by some kB.
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@robin-nitrokey
robin-nitrokey committed Apr 10, 2024
1 parent 83cf940 commit 8624e88
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1 change: 1 addition & 0 deletions Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,7 @@ littlefs2 = "0.4.0"
p256-cortex-m4 = { version = "0.1.0-alpha.6", features = ["prehash", "sec1-signatures"] }
salty = { version = "0.3.0", features = ["cose"] }
serde-indexed = "0.1.0"
paste = "1.0.14"

[dev-dependencies]
# Testing
Expand Down
56 changes: 17 additions & 39 deletions src/mechanisms.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,73 +10,51 @@
// The question of breaking down `reply_to` into smaller, more globally understandable pieces,
// should be revisited.

// TODO: rename to aes256-cbc-zero-iv
pub struct Aes256Cbc {}
pub struct Aes256Cbc;
mod aes256cbc;

pub struct Chacha8Poly1305 {}
pub struct Chacha8Poly1305;
mod chacha8poly1305;

pub struct SharedSecret {}
pub struct SharedSecret;
mod shared_secret;

pub struct Ed255 {}
pub struct Ed255;
mod ed255;

pub struct HmacBlake2s {}
pub struct HmacBlake2s;
#[cfg(feature = "hmac-blake2s")]
mod hmacblake2s;
#[cfg(not(feature = "hmac-blake2s"))]
impl crate::service::DeriveKey for HmacBlake2s {}
#[cfg(not(feature = "hmac-blake2s"))]
impl crate::service::Sign for HmacBlake2s {}
impl crate::service::MechanismImpl for HmacBlake2s {}

pub struct HmacSha1 {}
pub struct HmacSha1;
mod hmacsha1;

pub struct HmacSha256 {}
pub struct HmacSha256;
mod hmacsha256;

pub struct HmacSha512 {}
pub struct HmacSha512;
#[cfg(feature = "hmac-sha512")]
mod hmacsha512;
#[cfg(not(feature = "hmac-sha512"))]
impl crate::service::DeriveKey for HmacSha512 {}
#[cfg(not(feature = "hmac-sha512"))]
impl crate::service::Sign for HmacSha512 {}
impl crate::service::MechanismImpl for HmacSha512 {}

pub struct P256 {}
pub struct P256Prehashed {}
pub struct P256;
pub struct P256Prehashed;
mod p256;

pub struct Sha256 {}
pub struct Sha256;
mod sha256;

pub struct Tdes {}
pub struct Tdes;
mod tdes;

pub struct Totp {}
pub struct Totp;
mod totp;

pub struct Trng {}
pub struct Trng;
mod trng;

pub struct X255 {}
pub struct X255;
mod x255;

// pub enum MechanismEnum {
// NotImplemented,
// Ed255(ed255::Ed255),
// P256(p256::P256),
// }

// use crate::types::Mechanism;
// pub fn enum_to_type(mechanism: Mechanism) -> MechanismEnum {
// match mechanism {
// #[cfg(feature = "ed255")]
// Mechanism::Ed255 => MechanismEnum::Ed255(ed255::Ed255 {} ),
// #[cfg(feature = "p256")]
// Mechanism::P256 => MechanismEnum::P256(p256::P256 {} ),
// _ => MechanismEnum::NotImplemented,
// }
// }
29 changes: 9 additions & 20 deletions src/mechanisms/aes256cbc.rs
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Original file line number Diff line number Diff line change
@@ -1,16 +1,17 @@
use crate::api::{reply, request};
use crate::error::Error;
use crate::key;
use crate::service::{Decrypt, Encrypt, UnsafeInjectKey, WrapKey};
use crate::service::MechanismImpl;
use crate::store::keystore::Keystore;
use crate::types::{Mechanism, Message, ShortData};

const AES256_KEY_SIZE: usize = 32;

#[cfg(feature = "aes256-cbc")]
impl Encrypt for super::Aes256Cbc {
impl MechanismImpl for super::Aes256Cbc {
/// Encrypts the input *with zero IV*
fn encrypt(
&self,
keystore: &mut impl Keystore,
request: &request::Encrypt,
) -> Result<reply::Encrypt, Error> {
Expand Down Expand Up @@ -64,11 +65,9 @@ impl Encrypt for super::Aes256Cbc {
tag: ShortData::new(),
})
}
}

#[cfg(feature = "aes256-cbc")]
impl WrapKey for super::Aes256Cbc {
fn wrap_key(
&self,
keystore: &mut impl Keystore,
request: &request::WrapKey,
) -> Result<reply::WrapKey, Error> {
Expand All @@ -93,17 +92,15 @@ impl WrapKey for super::Aes256Cbc {
associated_data: request.associated_data.clone(),
nonce: request.nonce.clone(),
};
let encryption_reply = <super::Aes256Cbc>::encrypt(keystore, &encryption_request)?;
let encryption_reply = self.encrypt(keystore, &encryption_request)?;

let wrapped_key = encryption_reply.ciphertext;

Ok(reply::WrapKey { wrapped_key })
}
}

#[cfg(feature = "aes256-cbc")]
impl Decrypt for super::Aes256Cbc {
fn decrypt(
&self,
keystore: &mut impl Keystore,
request: &request::Decrypt,
) -> Result<reply::Decrypt, Error> {
Expand Down Expand Up @@ -158,11 +155,9 @@ impl Decrypt for super::Aes256Cbc {
plaintext: Some(plaintext),
})
}
}

#[cfg(feature = "aes256-cbc")]
impl UnsafeInjectKey for super::Aes256Cbc {
fn unsafe_inject_key(
&self,
keystore: &mut impl Keystore,
request: &request::UnsafeInjectKey,
) -> Result<reply::UnsafeInjectKey, Error> {
Expand All @@ -173,7 +168,7 @@ impl UnsafeInjectKey for super::Aes256Cbc {
let key_id = keystore.store_key(
request.attributes.persistence,
key::Secrecy::Secret,
key::Kind::Symmetric(request.raw_key.len()),
key::Kind::Symmetric(request.raw_key.len()).into(),
&request.raw_key,
)?;

Expand All @@ -182,10 +177,4 @@ impl UnsafeInjectKey for super::Aes256Cbc {
}

#[cfg(not(feature = "aes256-cbc"))]
impl UnsafeInjectKey for super::Aes256Cbc {}
#[cfg(not(feature = "aes256-cbc"))]
impl Decrypt for super::Aes256Cbc {}
#[cfg(not(feature = "aes256-cbc"))]
impl Encrypt for super::Aes256Cbc {}
#[cfg(not(feature = "aes256-cbc"))]
impl WrapKey for super::Aes256Cbc {}
impl MechanismImpl for super::Aes256Cbc {}
82 changes: 33 additions & 49 deletions src/mechanisms/chacha8poly1305.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ use rand_core::RngCore;
use crate::api::{reply, request};
use crate::error::Error;
use crate::key;
use crate::service::{Decrypt, Encrypt, GenerateKey, UnwrapKey, WrapKey};
use crate::service::MechanismImpl;
use crate::store::keystore::Keystore;
use crate::types::{Mechanism, Message, ShortData};

Expand All @@ -19,10 +19,27 @@ const TAG_LEN: usize = 16;
const KIND: key::Kind = key::Kind::Symmetric(KEY_LEN);
const KIND_NONCE: key::Kind = key::Kind::Symmetric32Nonce(NONCE_LEN);

#[inline(never)]
fn increment_nonce(nonce: &mut [u8]) -> Result<(), Error> {
assert_eq!(nonce.len(), NONCE_LEN);
let mut carry: u16 = 1;
for digit in nonce.iter_mut() {
let x = (*digit as u16) + carry;
*digit = x as u8;
carry = x >> 8;
}
if carry == 0 {
Ok(())
} else {
Err(Error::NonceOverflow)
}
}

#[cfg(feature = "chacha8-poly1305")]
impl GenerateKey for super::Chacha8Poly1305 {
impl MechanismImpl for super::Chacha8Poly1305 {
#[inline(never)]
fn generate_key(
&self,
keystore: &mut impl Keystore,
request: &request::GenerateKey,
) -> Result<reply::GenerateKey, Error> {
Expand All @@ -39,34 +56,16 @@ impl GenerateKey for super::Chacha8Poly1305 {
let key_id = keystore.store_key(
request.attributes.persistence,
key::Secrecy::Secret,
KIND_NONCE,
KIND_NONCE.into(),
&serialized,
)?;

Ok(reply::GenerateKey { key: key_id })
}
}

#[inline(never)]
fn increment_nonce(nonce: &mut [u8]) -> Result<(), Error> {
assert_eq!(nonce.len(), NONCE_LEN);
let mut carry: u16 = 1;
for digit in nonce.iter_mut() {
let x = (*digit as u16) + carry;
*digit = x as u8;
carry = x >> 8;
}
if carry == 0 {
Ok(())
} else {
Err(Error::NonceOverflow)
}
}

#[cfg(feature = "chacha8-poly1305")]
impl Decrypt for super::Chacha8Poly1305 {
#[inline(never)]
fn decrypt(
&self,
keystore: &mut impl Keystore,
request: &request::Decrypt,
) -> Result<reply::Decrypt, Error> {
Expand Down Expand Up @@ -104,12 +103,10 @@ impl Decrypt for super::Chacha8Poly1305 {
},
})
}
}

#[cfg(feature = "chacha8-poly1305")]
impl Encrypt for super::Chacha8Poly1305 {
#[inline(never)]
fn encrypt(
&self,
keystore: &mut impl Keystore,
request: &request::Encrypt,
) -> Result<reply::Encrypt, Error> {
Expand Down Expand Up @@ -165,12 +162,10 @@ impl Encrypt for super::Chacha8Poly1305 {
tag,
})
}
}

#[cfg(feature = "chacha8-poly1305")]
impl WrapKey for super::Chacha8Poly1305 {
#[inline(never)]
fn wrap_key(
&self,
keystore: &mut impl Keystore,
request: &request::WrapKey,
) -> Result<reply::WrapKey, Error> {
Expand All @@ -188,19 +183,17 @@ impl WrapKey for super::Chacha8Poly1305 {
associated_data: request.associated_data.clone(),
nonce: request.nonce.clone(),
};
let encryption_reply = <super::Chacha8Poly1305>::encrypt(keystore, &encryption_request)?;
let encryption_reply = self.encrypt(keystore, &encryption_request)?;

let wrapped_key =
crate::postcard_serialize_bytes(&encryption_reply).map_err(|_| Error::CborError)?;

Ok(reply::WrapKey { wrapped_key })
}
}

#[cfg(feature = "chacha8-poly1305")]
impl UnwrapKey for super::Chacha8Poly1305 {
#[inline(never)]
fn unwrap_key(
&self,
keystore: &mut impl Keystore,
request: &request::UnwrapKey,
) -> Result<reply::UnwrapKey, Error> {
Expand All @@ -219,13 +212,12 @@ impl UnwrapKey for super::Chacha8Poly1305 {
tag,
};

let serialized_key = if let Some(serialized_key) =
<super::Chacha8Poly1305>::decrypt(keystore, &decryption_request)?.plaintext
{
serialized_key
} else {
return Ok(reply::UnwrapKey { key: None });
};
let serialized_key =
if let Some(serialized_key) = self.decrypt(keystore, &decryption_request)?.plaintext {
serialized_key
} else {
return Ok(reply::UnwrapKey { key: None });
};

// TODO: probably change this to returning Option<key> too
let key::Key {
Expand All @@ -239,7 +231,7 @@ impl UnwrapKey for super::Chacha8Poly1305 {
request.attributes.persistence,
// using for signing keys... we need to know
key::Secrecy::Secret,
kind,
kind.into(),
&material,
)?;

Expand All @@ -248,12 +240,4 @@ impl UnwrapKey for super::Chacha8Poly1305 {
}

#[cfg(not(feature = "chacha8-poly1305"))]
impl Decrypt for super::Chacha8Poly1305 {}
#[cfg(not(feature = "chacha8-poly1305"))]
impl Encrypt for super::Chacha8Poly1305 {}
#[cfg(not(feature = "chacha8-poly1305"))]
impl WrapKey for super::Chacha8Poly1305 {}
#[cfg(not(feature = "chacha8-poly1305"))]
impl UnwrapKey for super::Chacha8Poly1305 {}
#[cfg(not(feature = "chacha8-poly1305"))]
impl GenerateKey for super::Chacha8Poly1305 {}
impl MechanismImpl for super::Chacha8Poly1305 {}
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