On Mon, Nov 07, 2022 at 06:51:26PM +0200, Ilari Liusvaara wrote:
>
> - Making sender structure to be dictionary makes it more complex to
> decode versus array structure, since implementation has to look up
> the required keys (and handle those being missing!) instead of
> just doing array indexing (after having ensured that array is big
> enough).
>
This might be artifact of CBOR library used, but here is some untested
code I wrote to pull apart PR9 and PR10 COSE_HPKE_Sender formats:
------------------------------------------------------------------------
use btls_aux_cbor::CBOR;
use core::convert::TryInto;
macro_rules! throw { ($x:expr) => { $x.ok_or(())? } }
fn __get_u16(val: &CBOR) -> Result<u16, ()>
{
throw!(val.as_integer()).try_into().map_err(|_|())
}
pub struct HpkeSender<'a>
{
pub kem: Option<u16>,
pub kdf: u16,
pub aead: u16,
pub enc: &'a [u8],
}
impl<'a> HpkeSender<'a>
{
pub fn decode_pr9(cbor: &'a CBOR) -> Result<HpkeSender<'a>, ()>
{
let cbor = throw!(cbor.as_dictionary());
let kem = cbor.get(&CBOR::Integer(1));
let kdf = throw!(cbor.get(&CBOR::Integer(2)));
let aead = throw!(cbor.get(&CBOR::Integer(3)));
let enc = throw!(cbor.get(&CBOR::Integer(4)));
for key in cbor.keys() {
let key = throw!(key.as_integer());
if key < 1 || key > 4 { return Err(()); }
}
Ok(HpkeSender{
kem: kem.map(__get_u16).transpose()?,
kdf: __get_u16(kdf)?,
aead: __get_u16(aead)?,
enc: throw!(enc.as_octets()),
})
}
pub fn decode_pr10(cbor: &'a CBOR) -> Result<HpkeSender<'a>, ()>
{
let cbor = throw!(cbor.as_array());
if cbor.len() < 3 || cbor.len() > 4 { return Err(()); }
let kdf = &cbor[0];
let aead = &cbor[1];
let enc = &cbor[2];
let kem = cbor.get(3);
Ok(HpkeSender{
kem: kem.map(__get_u16).transpose()?,
kdf: __get_u16(kdf)?,
aead: __get_u16(aead)?,
enc: throw!(enc.as_octets()),
})
}
}
------------------------------------------------------------------------
The difference is certainly much smaller than I expected...
-Ilari
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