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Handles variable-length nonce #125

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Handles variable-length nonce #125

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0bb055f
Handles variable-length nonce
masihyeganeh Mar 11, 2020
d868d63
Handles variable-length nonce
masihyeganeh Mar 11, 2020
2b66126
Delete unused U12
masihyeganeh Mar 11, 2020
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12 changes: 8 additions & 4 deletions aes-gcm/src/ctr.rs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
//! Counter mode implementation

use block_cipher_trait::generic_array::{
typenum::{Unsigned, U12, U16},
typenum::{Unsigned, U16},
ArrayLength, GenericArray,
};
use block_cipher_trait::BlockCipher;
Expand Down Expand Up @@ -35,10 +35,14 @@ where
B::ParBlocks: ArrayLength<GenericArray<u8, B::BlockSize>>,
{
/// Instantiate a new CTR instance
pub fn new(nonce: &GenericArray<u8, U12>) -> Self {
pub fn new(nonce: &[u8]) -> Self {
let mut counter_block = GenericArray::default();
counter_block[..12].copy_from_slice(nonce.as_slice());
counter_block[15] = 1;
if nonce.len() == 12 {
counter_block[..12].copy_from_slice(nonce);
counter_block[15] = 1;
} else {
counter_block[..].copy_from_slice(nonce);
}

Self {
block_cipher: PhantomData,
Expand Down
29 changes: 24 additions & 5 deletions aes-gcm/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -183,23 +183,32 @@ where
B: BlockCipher<BlockSize = U16>,
B::ParBlocks: ArrayLength<GenericArray<u8, B::BlockSize>>,
{
type NonceSize = U12;
type TagSize = U16;
type CiphertextOverhead = U0;

fn encrypt_in_place_detached(
&self,
nonce: &GenericArray<u8, Self::NonceSize>,
nonce: &[u8],
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This would require a change in the Aead trait. See RustCrypto/traits#65

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Yeah. I did that too

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Aah, apologies!

associated_data: &[u8],
buffer: &mut [u8],
) -> Result<Tag, Error> {
if buffer.len() as u64 > P_MAX || associated_data.len() as u64 > A_MAX {
return Err(Error);
}

// Handles variable-length nonce
let nonce = if nonce.len() != 12 {
let ghash = &mut self.ghash.clone();
ghash.update_padded(nonce);
let nonce = ghash.result_reset().into_bytes().to_vec();
nonce
} else {
nonce.to_vec()
};

// TODO(tarcieri): interleave encryption with GHASH
// See: <https://github.com/RustCrypto/AEADs/issues/74>
let mut ctr = Ctr32::new(nonce);
let mut ctr = Ctr32::new(nonce.as_ref());
ctr.seek(1);
ctr.apply_keystream(&self.cipher, buffer);

Expand All @@ -212,7 +221,7 @@ where

fn decrypt_in_place_detached(
&self,
nonce: &GenericArray<u8, Self::NonceSize>,
nonce: &[u8],
associated_data: &[u8],
buffer: &mut [u8],
tag: &Tag,
Expand All @@ -221,10 +230,20 @@ where
return Err(Error);
}

// Handles variable-length nonce
let nonce = if nonce.len() != 12 {
let ghash = &mut self.ghash.clone();
ghash.update_padded(nonce);
let nonce = ghash.result_reset().into_bytes().to_vec();
nonce
} else {
nonce.to_vec()
};

// TODO(tarcieri): interleave encryption with GHASH
// See: <https://github.com/RustCrypto/AEADs/issues/74>
let mut expected_tag = compute_tag(&mut self.ghash.clone(), associated_data, buffer);
let mut ctr = Ctr32::new(nonce);
let mut ctr = Ctr32::new(nonce.as_ref());
ctr.apply_keystream(&self.cipher, expected_tag.as_mut_slice());

use subtle::ConstantTimeEq;
Expand Down