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chacha20_poly1305_openssh: Minimize and document panicking. #2228

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merged 2 commits into from
Jan 16, 2025
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chacha20_poly1305_openssh: Minimize and document panicking. #2228

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53adab1
chacha20_poly1305_openssh: Don't panic in `open_in_place`.
briansmith Jan 16, 2025
4f65d89
chacha20_poly1305_openssh: Document panic in `seal_in_place`.
briansmith Jan 16, 2025
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10 changes: 10 additions & 0 deletions src/aead/chacha20_poly1305_openssh.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,10 @@ impl SealingKey {
/// `padding_length||payload||random padding`. It will be overwritten by
/// `encrypted_packet_length||ciphertext`, where `encrypted_packet_length`
/// is encrypted with `K_1` and `ciphertext` is encrypted by `K_2`.
///
/// # Panics
///
/// Panics if `plaintext_in_ciphertext_out.len() < PACKET_LENGTH_LEN`.
pub fn seal_in_place(
&self,
sequence_number: u32,
Expand Down Expand Up @@ -126,6 +130,10 @@ impl OpeningKey {
ciphertext_in_plaintext_out: &'a mut [u8],
tag: &[u8; TAG_LEN],
) -> Result<&'a [u8], error::Unspecified> {
if ciphertext_in_plaintext_out.len() < PACKET_LENGTH_LEN {
return Err(error::Unspecified);
}

let mut counter = make_counter(sequence_number);

// We must verify the tag before decrypting so that
Expand All @@ -134,7 +142,9 @@ impl OpeningKey {
let poly_key = derive_poly1305_key(&self.key.k_2, counter.increment());
verify(poly_key, ciphertext_in_plaintext_out, tag)?;

// Won't panic because the length was checked above.
let plaintext_in_ciphertext_out = &mut ciphertext_in_plaintext_out[PACKET_LENGTH_LEN..];

self.key
.k_2
.encrypt_in_place(counter, plaintext_in_ciphertext_out);
Expand Down