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aes: implement Zeroize for aes keys #310

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merged 1 commit into from
Mar 18, 2022
Merged

aes: implement Zeroize for aes keys #310

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5 changes: 3 additions & 2 deletions Cargo.lock
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2 changes: 1 addition & 1 deletion aes/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@ categories = ["cryptography", "no-std"]
[dependencies]
cfg-if = "1"
cipher = "0.4.2"
zeroize = { version = "1.5.4", optional = true, default_features = false }

[target.'cfg(any(target_arch = "aarch64", target_arch = "x86_64", target_arch = "x86"))'.dependencies]
cpufeatures = "0.2"
Expand All @@ -25,7 +26,6 @@ hex-literal = "0.3"

[features]
hazmat = [] # Expose cryptographically hazardous APIs
zeroize = ["cipher/zeroize"]

[package.metadata.docs.rs]
all-features = true
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25 changes: 25 additions & 0 deletions aes/src/armv8.rs
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Expand Up @@ -122,6 +122,9 @@ macro_rules! define_aes_impl {
}
}

#[cfg(feature = "zeroize")]
impl zeroize::ZeroizeOnDrop for $name {}

#[doc=$doc]
#[doc = "block cipher (encrypt-only)"]
#[derive(Clone)]
Expand Down Expand Up @@ -172,6 +175,17 @@ macro_rules! define_aes_impl {
}
}

impl Drop for $name_enc {
#[inline]
fn drop(&mut self) {
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@newpavlov newpavlov Mar 18, 2022 •
edited

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It could be worth to add #[inline] attribute here and in other Drop impls. Otherwise, without LTO Rust will not be able to inline it.

Also, are we sure that Rust always handles empty Drop impls in the same way as unimplemented Drop? I vaguely remember that Rust has a special handling of Drop-free types.

Personally, I think that having a Drop impl gated on zeroize is fine (I've used such approach in other crates), especially if we will use doc_cfg to expose it in docs.

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As far as I'm aware the only difference between implementing Drop and not implementing it is being able to implement Copy. The reference also does not seem to say much more about that.

The only other differences I could think of are performance issues, such as not having to track drop flags and not running an empty destructor (though inlining should prevent that). I added the inline attribute to all drop functions now.

In general I agree with @tarcieri that conditionally implementing Drop (or any trait) based on a not obviously related feature could lead to problems.

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@tarcieri tarcieri Mar 18, 2022 •
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If nothing else the bounds are different, although whether Drop bounds should be used/allowed at all is a matter of debate. Nevertheless, they do.

The other major difference is it's not possible to move fields out of a struct which impls Drop, although that's not happening in the current implementation so it's not a major issue.

I think Drop is magical enough conditionally dropping based on whether or not features are impl'd is a bit weird.

#[cfg(feature = "zeroize")]
zeroize::Zeroize::zeroize(&mut self.round_keys);
}
}

#[cfg(feature = "zeroize")]
impl zeroize::ZeroizeOnDrop for $name_enc {}

#[doc=$doc]
#[doc = "block cipher (decrypt-only)"]
#[derive(Clone)]
Expand Down Expand Up @@ -235,6 +249,17 @@ macro_rules! define_aes_impl {
}
}

impl Drop for $name_dec {
#[inline]
fn drop(&mut self) {
#[cfg(feature = "zeroize")]
zeroize::Zeroize::zeroize(&mut self.round_keys);
}
}

#[cfg(feature = "zeroize")]
impl zeroize::ZeroizeOnDrop for $name_dec {}

pub(crate) struct $name_back_enc<'a>(&'a $name_enc);

impl<'a> BlockSizeUser for $name_back_enc<'a> {
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42 changes: 42 additions & 0 deletions aes/src/autodetect.rs
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Expand Up @@ -180,6 +180,20 @@ macro_rules! define_aes_impl {
}
}

impl Drop for $name {
#[inline]
fn drop(&mut self) {
if self.token.get() {
unsafe { ManuallyDrop::drop(&mut self.inner.intrinsics) };
} else {
unsafe { ManuallyDrop::drop(&mut self.inner.soft) };
};
}
}

#[cfg(feature = "zeroize")]
impl zeroize::ZeroizeOnDrop for $name {}

#[doc=$doc]
#[doc = "block cipher (encrypt-only)"]
pub struct $name_enc {
Expand Down Expand Up @@ -266,6 +280,20 @@ macro_rules! define_aes_impl {
}
}

impl Drop for $name_enc {
#[inline]
fn drop(&mut self) {
if self.token.get() {
unsafe { ManuallyDrop::drop(&mut self.inner.intrinsics) };
} else {
unsafe { ManuallyDrop::drop(&mut self.inner.soft) };
};
}
}

#[cfg(feature = "zeroize")]
impl zeroize::ZeroizeOnDrop for $name_enc {}

#[doc=$doc]
#[doc = "block cipher (decrypt-only)"]
pub struct $name_dec {
Expand Down Expand Up @@ -380,6 +408,20 @@ macro_rules! define_aes_impl {
f.write_str(stringify!($name_dec))
}
}

impl Drop for $name_dec {
#[inline]
fn drop(&mut self) {
if self.token.get() {
unsafe { ManuallyDrop::drop(&mut self.inner.intrinsics) };
} else {
unsafe { ManuallyDrop::drop(&mut self.inner.soft) };
};
}
}

#[cfg(feature = "zeroize")]
impl zeroize::ZeroizeOnDrop for $name_dec {}
};
}

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74 changes: 74 additions & 0 deletions aes/src/lib.rs
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Expand Up @@ -159,3 +159,77 @@ use cipher::{
pub type Block = GenericArray<u8, U16>;
/// Eight 128-bit AES blocks
pub type Block8 = GenericArray<Block, U8>;

#[cfg(test)]
mod tests {
#[cfg(feature = "zeroize")]
#[test]
fn zeroize_works() {
use super::soft;

fn test_for<T: zeroize::ZeroizeOnDrop>(val: T) {
use core::mem::{size_of, ManuallyDrop};

let mut val = ManuallyDrop::new(val);
let ptr = &val as *const _ as *const u8;
let len = size_of::<ManuallyDrop<T>>();

unsafe { ManuallyDrop::drop(&mut val) };

let slice = unsafe { core::slice::from_raw_parts(ptr, len) };

assert!(slice.iter().all(|&byte| byte == 0));
}

let key_128 = [42; 16].into();
let key_192 = [42; 24].into();
let key_256 = [42; 32].into();

use cipher::KeyInit as _;
test_for(soft::Aes128::new(&key_128));
test_for(soft::Aes128Enc::new(&key_128));
test_for(soft::Aes128Dec::new(&key_128));
test_for(soft::Aes192::new(&key_192));
test_for(soft::Aes192Enc::new(&key_192));
test_for(soft::Aes192Dec::new(&key_192));
test_for(soft::Aes256::new(&key_256));
test_for(soft::Aes256Enc::new(&key_256));
test_for(soft::Aes256Dec::new(&key_256));

#[cfg(all(any(target_arch = "x86", target_arch = "x86_64"), not(aes_force_soft)))]
{
use super::ni;

cpufeatures::new!(aes_intrinsics, "aes");
if aes_intrinsics::get() {
test_for(ni::Aes128::new(&key_128));
test_for(ni::Aes128Enc::new(&key_128));
test_for(ni::Aes128Dec::new(&key_128));
test_for(ni::Aes192::new(&key_192));
test_for(ni::Aes192Enc::new(&key_192));
test_for(ni::Aes192Dec::new(&key_192));
test_for(ni::Aes256::new(&key_256));
test_for(ni::Aes256Enc::new(&key_256));
test_for(ni::Aes256Dec::new(&key_256));
}
}

#[cfg(all(target_arch = "aarch64", aes_armv8, not(aes_force_soft)))]
{
use super::armv8;

cpufeatures::new!(aes_intrinsics, "aes");
if aes_intrinsics::get() {
test_for(armv8::Aes128::new(&key_128));
test_for(armv8::Aes128Enc::new(&key_128));
test_for(armv8::Aes128Dec::new(&key_128));
test_for(armv8::Aes192::new(&key_192));
test_for(armv8::Aes192Enc::new(&key_192));
test_for(armv8::Aes192Dec::new(&key_192));
test_for(armv8::Aes256::new(&key_256));
test_for(armv8::Aes256Enc::new(&key_256));
test_for(armv8::Aes256Dec::new(&key_256));
}
}
}
}
25 changes: 25 additions & 0 deletions aes/src/ni.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -133,6 +133,9 @@ macro_rules! define_aes_impl {
}
}

#[cfg(feature = "zeroize")]
impl zeroize::ZeroizeOnDrop for $name {}

#[doc=$doc]
#[doc = "block cipher (encrypt-only)"]
#[derive(Clone)]
Expand Down Expand Up @@ -185,6 +188,17 @@ macro_rules! define_aes_impl {
}
}

impl Drop for $name_enc {
#[inline]
fn drop(&mut self) {
#[cfg(feature = "zeroize")]
zeroize::Zeroize::zeroize(&mut self.round_keys);
}
}

#[cfg(feature = "zeroize")]
impl zeroize::ZeroizeOnDrop for $name_enc {}

#[doc=$doc]
#[doc = "block cipher (decrypt-only)"]
#[derive(Clone)]
Expand Down Expand Up @@ -248,6 +262,17 @@ macro_rules! define_aes_impl {
}
}

impl Drop for $name_dec {
#[inline]
fn drop(&mut self) {
#[cfg(feature = "zeroize")]
zeroize::Zeroize::zeroize(&mut self.round_keys);
}
}

#[cfg(feature = "zeroize")]
impl zeroize::ZeroizeOnDrop for $name_dec {}

pub(crate) struct $name_back_enc<'a>(&'a $name_enc);

impl<'a> BlockSizeUser for $name_back_enc<'a> {
Expand Down
17 changes: 17 additions & 0 deletions aes/src/soft.rs
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Expand Up @@ -112,6 +112,17 @@ macro_rules! define_aes_impl {
}
}

impl Drop for $name {
#[inline]
fn drop(&mut self) {
#[cfg(feature = "zeroize")]
zeroize::Zeroize::zeroize(&mut self.keys);
}
}

#[cfg(feature = "zeroize")]
impl zeroize::ZeroizeOnDrop for $name {}

#[doc=$doc]
#[doc = "block cipher (encrypt-only)"]
#[derive(Clone)]
Expand Down Expand Up @@ -162,6 +173,9 @@ macro_rules! define_aes_impl {
}
}

#[cfg(feature = "zeroize")]
impl zeroize::ZeroizeOnDrop for $name_enc {}

#[doc=$doc]
#[doc = "block cipher (decrypt-only)"]
#[derive(Clone)]
Expand Down Expand Up @@ -228,6 +242,9 @@ macro_rules! define_aes_impl {
}
}

#[cfg(feature = "zeroize")]
impl zeroize::ZeroizeOnDrop for $name_dec {}

pub(crate) struct $name_back_enc<'a>(&'a $name);

impl<'a> BlockSizeUser for $name_back_enc<'a> {
Expand Down