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aes-gcm internals: Clarify in_out processing. #2205

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merged 2 commits into from
Jan 1, 2025
Merged

aes-gcm internals: Clarify in_out processing. #2205

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e92d9f2
aes-gcm internals: Clarify slicing operations in X86-64 integrated case.
briansmith Jan 1, 2025
6d39c75
aes_gcm internals: Clarify `in_out` processing in `open_strided`.
briansmith Jan 1, 2025
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49 changes: 29 additions & 20 deletions src/aead/aes_gcm.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -316,34 +316,34 @@ pub(super) fn open(
xi,
)
};
let in_out = match in_out_slice.get_mut(processed..) {
Some(remaining) => remaining,
None => {
let in_out_slice = in_out_slice.get_mut(processed..).unwrap_or_else(|| {
// This can't happen. If it did, then the assembly already
// caused a buffer overflow.
unreachable!()
});
// Authenticate any remaining whole blocks.
let in_out = Overlapping::new(in_out_slice, src.clone()).unwrap_or_else(
|SrcIndexError { .. }| {
// This can't happen. If it did, then the assembly already
// caused a buffer overflow.
// overwrote part of the remaining input.
unreachable!()
}
};
// Authenticate any remaining whole blocks.
let input = match in_out.get(src.clone()) {
Some(remaining_input) => remaining_input,
None => unreachable!(),
};
let (whole, _) = slice::as_chunks(input);
},
);
let (whole, _) = slice::as_chunks(in_out.input());
auth.update_blocks(whole);

let whole_len = slice::flatten(whole).len();

// Decrypt any remaining whole blocks.
let whole = Overlapping::new(&mut in_out[..(src.start + whole_len)], src.clone())
let whole = Overlapping::new(&mut in_out_slice[..(src.start + whole_len)], src.clone())
.map_err(error::erase::<SrcIndexError>)?;
aes_key.ctr32_encrypt_within(whole, &mut ctr);

let in_out = match in_out.get_mut(whole_len..) {
let in_out_slice = match in_out_slice.get_mut(whole_len..) {
Some(partial) => partial,
None => unreachable!(),
};
open_finish(aes_key, auth, in_out, src, ctr, tag_iv)
open_finish(aes_key, auth, in_out_slice, src, ctr, tag_iv)
}

#[cfg(target_arch = "aarch64")]
Expand Down Expand Up @@ -422,12 +422,14 @@ pub(super) fn open(
fn open_strided<A: aes::EncryptBlock + aes::EncryptCtr32, G: gcm::UpdateBlocks + gcm::Gmult>(
Combo { aes_key, gcm_key }: &Combo<A, G>,
aad: Aad<&[u8]>,
in_out: &mut [u8],
in_out_slice: &mut [u8],
src: RangeFrom<usize>,
mut ctr: Counter,
tag_iv: aes::Iv,
) -> Result<Tag, error::Unspecified> {
let input = in_out.get(src.clone()).ok_or(error::Unspecified)?;
let in_out =
Overlapping::new(in_out_slice, src.clone()).map_err(error::erase::<SrcIndexError>)?;
let input = in_out.input();
let input_len = input.len();

let mut auth = gcm::Context::new(gcm_key, aad, input_len)?;
Expand All @@ -445,7 +447,7 @@ fn open_strided<A: aes::EncryptBlock + aes::EncryptCtr32, G: gcm::UpdateBlocks +
chunk_len = whole_len - output;
}

let ciphertext = &in_out[input..][..chunk_len];
let ciphertext = &in_out_slice[input..][..chunk_len];
let (ciphertext, leftover) = slice::as_chunks(ciphertext);
debug_assert_eq!(leftover.len(), 0);
if ciphertext.is_empty() {
Expand All @@ -454,7 +456,7 @@ fn open_strided<A: aes::EncryptBlock + aes::EncryptCtr32, G: gcm::UpdateBlocks +
auth.update_blocks(ciphertext);

let chunk = Overlapping::new(
&mut in_out[output..][..(chunk_len + in_prefix_len)],
&mut in_out_slice[output..][..(chunk_len + in_prefix_len)],
in_prefix_len..,
)
.map_err(error::erase::<SrcIndexError>)?;
Expand All @@ -464,7 +466,14 @@ fn open_strided<A: aes::EncryptBlock + aes::EncryptCtr32, G: gcm::UpdateBlocks +
}
}

open_finish(aes_key, auth, &mut in_out[whole_len..], src, ctr, tag_iv)
open_finish(
aes_key,
auth,
&mut in_out_slice[whole_len..],
src,
ctr,
tag_iv,
)
}

fn open_finish<A: aes::EncryptBlock, G: gcm::Gmult>(
Expand Down