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tesla: remove chain status from Chain
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This removes the chain status from the Chain. Since the chain status
can change from don't use to operational/test at any moment but the
Chain is associated with a key and propagated to the next TESLA key
after validation, it does not make sense to store the status in the
Chain.
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@daniestevez
daniestevez committed Jan 16, 2024
1 parent a988893 commit b757f77
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Showing 3 changed files with 59 additions and 53 deletions.
31 changes: 26 additions & 5 deletions src/navmessage.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@
//! the [`Osnma`](crate::Osnma) black box, but it can also be used directly
//! if finer control is needed.
use crate::bitfields::{Adkd, Mack};
use crate::bitfields::{Adkd, Mack, NmaStatus};
use crate::storage::StaticStorage;
use crate::tesla::Key;
use crate::types::{BitSlice, InavBand, InavWord};
Expand Down Expand Up @@ -310,7 +310,10 @@ impl<S: StaticStorage> CollectNavMessage<S> {
/// `prna` is the authenticating PRN, which is the SVN that has transmitted
/// the MACK message. The `gst_mack` parameter should be the GST
/// corresponding to the start of the subframe when the MACK message was
/// transmitted.
/// transmitted. The `nma_status` parameter should be the value of the NMA
/// status field in the current NMA header. The NMA header does not need to
/// be validated using the DSM-KROOT, since a forged or incorrect NMA header
/// will simply make tag validation fail.
///
/// This function ignores the ADKD=12 (Slow MAC) tags in the MACK message,
/// since they do not correspond to `key`.
Expand All @@ -320,6 +323,7 @@ impl<S: StaticStorage> CollectNavMessage<S> {
key: &Key<Validated>,
prna: Svn,
gst_mack: Gst,
nma_status: NmaStatus,
) {
log::info!("{} tag0 at {:?} COP = {}", prna, gst_mack, mack.cop());
let gst_navmessage = gst_mack.add_seconds(-30);
Expand All @@ -336,6 +340,7 @@ impl<S: StaticStorage> CollectNavMessage<S> {
u8::from(prna),
prna,
0,
nma_status,
&navdata,
self.ced_and_status_iter_authbits_mut(),
);
Expand Down Expand Up @@ -378,6 +383,7 @@ impl<S: StaticStorage> CollectNavMessage<S> {
prnd,
prna,
j,
nma_status,
&navdata,
self.ced_and_status_iter_authbits_mut(),
);
Expand All @@ -402,6 +408,7 @@ impl<S: StaticStorage> CollectNavMessage<S> {
prnd,
prna,
j,
nma_status,
&navdata,
self.timing_parameters_iter_authbits_mut(),
);
Expand Down Expand Up @@ -432,7 +439,10 @@ impl<S: StaticStorage> CollectNavMessage<S> {
/// message). The `prna` is the authenticating PRN, which is the SVN that
/// has transmitted the MACK message. The `gst_mack` parameter should be the
/// GST corresponding to the start of the subframe when the MACK message was
/// transmitted.
/// transmitted. The `nma_status` parameter should be the value of the NMA
/// status field in the current NMA header. The NMA header does not need to
/// be validated using the DSM-KROOT, since a forged or incorrect NMA header
/// will simply make tag validation fail.
///
/// This function ignores all the other tags in the MACK message, since they
/// do not correspond to `key`.
Expand All @@ -442,6 +452,7 @@ impl<S: StaticStorage> CollectNavMessage<S> {
key: &Key<Validated>,
prna: Svn,
gst_mack: Gst,
nma_status: NmaStatus,
) {
let gst_navmessage = gst_mack.add_seconds(-30);
for j in 1..mack.num_tags() {
Expand Down Expand Up @@ -476,6 +487,7 @@ impl<S: StaticStorage> CollectNavMessage<S> {
prnd,
prna,
j,
nma_status,
&navdata,
self.ced_and_status_iter_authbits_mut(),
);
Expand All @@ -493,13 +505,22 @@ impl<S: StaticStorage> CollectNavMessage<S> {
prnd: u8,
prna: Svn,
tag_idx: usize,
nma_status: NmaStatus,
navdata: &dyn AuthBits,
to_add_authbits: impl Iterator<Item = &'a mut dyn AuthBits>,
) -> bool {
let ctr = (tag_idx + 1).try_into().unwrap();
let ret = match tag_idx {
0 => key.validate_tag0(tag, gst_tag, prna, navdata.message_bits()),
_ => key.validate_tag(tag, gst_tag, prnd, prna, ctr, navdata.message_bits()),
0 => key.validate_tag0(tag, gst_tag, prna, nma_status, navdata.message_bits()),
_ => key.validate_tag(
tag,
gst_tag,
prnd,
prna,
ctr,
nma_status,
navdata.message_bits(),
),
};
if ret {
log::info!(
Expand Down
19 changes: 12 additions & 7 deletions src/osnma.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -239,7 +239,7 @@ impl<S: StaticStorage> OsnmaDsm<S> {
self.data.process_dsm(dsm, nma_header);
}

self.data.validate_key(mack, gst);
self.data.validate_key(mack, gst, nma_header.nma_status());
}
}

Expand Down Expand Up @@ -362,7 +362,7 @@ impl<S: StaticStorage> OsnmaData<S> {
}
}

fn validate_key(&mut self, mack: &MackMessage, gst: Gst) {
fn validate_key(&mut self, mack: &MackMessage, gst: Gst, nma_status: NmaStatus) {
let Some(current_key) = self.key.current_key() else {
log::info!("no valid TESLA key for the chain in force. unable to validate MACK key");
return;
Expand Down Expand Up @@ -394,7 +394,7 @@ impl<S: StaticStorage> OsnmaData<S> {
new_valid_key,
current_key
);
self.process_tags(&new_valid_key);
self.process_tags(&new_valid_key, nma_status);
self.key.store_key(new_valid_key);
}
Err(e) => log::error!(
Expand All @@ -408,7 +408,7 @@ impl<S: StaticStorage> OsnmaData<S> {
}
}

fn process_tags(&mut self, current_key: &Key<Validated>) {
fn process_tags(&mut self, current_key: &Key<Validated>, nma_status: NmaStatus) {
if self.dont_use {
return;
}
Expand All @@ -428,7 +428,7 @@ impl<S: StaticStorage> OsnmaData<S> {
);
if let Some(mack) = Self::validate_mack(mack, current_key, svn, gst_mack) {
self.navmessage
.process_mack(mack, current_key, svn, gst_mack);
.process_mack(mack, current_key, svn, gst_mack, nma_status);
};
}
}
Expand All @@ -445,8 +445,13 @@ impl<S: StaticStorage> OsnmaData<S> {
// Note that slowmac_key is used for validation of the MACK, while
// current_key is used for validation of the Slow MAC tags it contains.
if let Some(mack) = Self::validate_mack(mack, &slowmac_key, svn, gst_slowmac) {
self.navmessage
.process_mack_slowmac(mack, current_key, svn, gst_slowmac);
self.navmessage.process_mack_slowmac(
mack,
current_key,
svn,
gst_slowmac,
nma_status,
);
}
}
}
Expand Down
62 changes: 21 additions & 41 deletions src/tesla.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -33,9 +33,7 @@ const MAX_KEY_BYTES: usize = 32;
/// constructed from a DSK-KROOT message using [`Chain::from_dsm_kroot`].
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub struct Chain {
status: ChainStatus,
id: u8,
// TODO: decide if CPKS needs to be included here (and how)
hash_function: HashFunction,
mac_function: MacFunction,
key_size_bytes: usize,
Expand All @@ -44,22 +42,6 @@ pub struct Chain {
alpha: u64,
}

/// Chain status.
///
/// This gives the chain status for a valid TESLA chain. This roughly
/// corresponds to the NMA status [`NmaStatus`],
/// but "don't use" and "reserved" are not considered valid statuses for a TESLA
/// chain.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub enum ChainStatus {
/// Test (corresponds to NMAS = 1).
Test,
/// Operational (corresponds to NMAS = 2).
Operational,
/// Don't use (corresponds to NMAS = 3).
DontUse,
}

/// Hash function.
///
/// This gives the hash function used by the TESLA chain. Its values correspond
Expand Down Expand Up @@ -98,12 +80,6 @@ impl Chain {
nma_header: NmaHeader<NotValidated>,
dsm_kroot: DsmKroot,
) -> Result<Chain, ChainError> {
let status = match nma_header.nma_status() {
NmaStatus::Test => ChainStatus::Test,
NmaStatus::Operational => ChainStatus::Operational,
NmaStatus::DontUse => ChainStatus::DontUse,
NmaStatus::Reserved => return Err(ChainError::ReservedField),
};
let hash_function = match dsm_kroot.hash_function() {
bitfields::HashFunction::Sha256 => HashFunction::Sha256,
bitfields::HashFunction::Sha3_256 => HashFunction::Sha3_256,
Expand All @@ -123,7 +99,6 @@ impl Chain {
};
let tag_size_bits = dsm_kroot.tag_size().ok_or(ChainError::ReservedField)?;
Ok(Chain {
status,
id: nma_header.chain_id(),
hash_function,
mac_function,
Expand All @@ -134,11 +109,6 @@ impl Chain {
})
}

/// Gives the status of the TESLA chain.
pub fn chain_status(&self) -> ChainStatus {
self.status
}

/// Gives the chain ID of the TESLA chain.
pub fn chain_id(&self) -> u8 {
self.id
Expand Down Expand Up @@ -806,7 +776,10 @@ impl Key<Validated> {
/// according to Section 6.7 in the ICD. The `ctr` parameter is the index of
/// the tag, where the first tag in a MACK message has `ctr = 1`. Note that
/// [`Key::validate_tag0`] should be used to validate the tag0 in a MACK
/// message instead of this function.
/// message instead of this function. The `nma_status` parameter should be
/// the value of the NMA status field in the current NMA header. The NMA
/// header does not need to be validated using the DSM-KROOT, since a forged
/// or incorrect NMA header will simply make tag validation fail.
///
/// Note that the navigation data `navdata` must correspond to the previous
/// subframe of the tag, and the key `self` must correspond to the next
Expand All @@ -817,18 +790,20 @@ impl Key<Validated> {
///
/// This returns `true` if the validation was succesful. Otherwise, it
/// returns `false`.
#[allow(clippy::too_many_arguments)]
pub fn validate_tag(
&self,
tag: &BitSlice,
tag_gst: Gst,
prnd: u8,
prna: Svn,
ctr: u8,
nma_status: NmaStatus,
navdata: &BitSlice,
) -> bool {
let mut mac = self.mac_digest();
mac.update(&[prnd]);
self.update_common_tag_message(&mut mac, tag_gst, prna, ctr, navdata);
self.update_common_tag_message(&mut mac, tag_gst, prna, ctr, nma_status, navdata);
self.check_common(mac, tag)
}

Expand All @@ -840,7 +815,11 @@ impl Key<Validated> {
///
/// The `tag_gst` parameter should give the GST at the start of the subframe
/// when the `tag` was transmitted. The `prna` parameter corresponds to the
/// SVN of the satellite that transmitted the tag0.
/// SVN of the satellite that transmitted the tag0. The `nma_status`
/// parameter should be the value of the NMA status field in the current NMA
/// header. The NMA header does not need to be validated using the
/// DSM-KROOT, since a forged or incorrect NMA header will simply make tag
/// validation fail.
///
/// Note that the navigation data `navdata` must correspond to the previous
/// subframe of the tag0, and the key `self` must correspond to the next
Expand All @@ -853,10 +832,11 @@ impl Key<Validated> {
tag0: &BitSlice,
tag_gst: Gst,
prna: Svn,
nma_status: NmaStatus,
navdata: &BitSlice,
) -> bool {
let mut mac = self.mac_digest();
self.update_common_tag_message(&mut mac, tag_gst, prna, 1, navdata);
self.update_common_tag_message(&mut mac, tag_gst, prna, 1, nma_status, navdata);
self.check_common(mac, tag0)
}

Expand All @@ -871,6 +851,7 @@ impl Key<Validated> {
gst: Gst,
prna: Svn,
ctr: u8,
nma_status: NmaStatus,
navdata: &BitSlice,
) {
// This is large enough to fit all the message for ADKD=0 and 12
Expand All @@ -884,10 +865,11 @@ impl Key<Validated> {
buffer[5] = ctr;
let remaining_bits = BitSlice::from_slice_mut(&mut buffer[6..]);
const STATUS_BITS: usize = 2;
remaining_bits[..STATUS_BITS].store_be(match self.chain.status {
ChainStatus::Test => 1,
ChainStatus::Operational => 2,
ChainStatus::DontUse => 3,
remaining_bits[..STATUS_BITS].store_be(match nma_status {
NmaStatus::Reserved => 0,
NmaStatus::Test => 1,
NmaStatus::Operational => 2,
NmaStatus::DontUse => 3,
});
remaining_bits[STATUS_BITS..STATUS_BITS + navdata.len()].copy_from_bitslice(navdata);
let message_bytes = FIXED_SIZE + (STATUS_BITS + navdata.len() + 7) / 8;
Expand Down Expand Up @@ -1000,7 +982,6 @@ mod test {
fn test_chain() -> Chain {
// Active chain on 2022-03-07 ~09:00 UTC
Chain {
status: ChainStatus::Test,
id: 1,
hash_function: HashFunction::Sha256,
mac_function: MacFunction::HmacSha256,
Expand All @@ -1014,7 +995,6 @@ mod test {
fn test_chain_2023() -> Chain {
// Active chain on 2023-12-12 ~10:00 UTC
Chain {
status: ChainStatus::Test,
id: 0,
hash_function: HashFunction::Sha256,
mac_function: MacFunction::HmacSha256,
Expand Down Expand Up @@ -1082,7 +1062,7 @@ mod test {
01 7f fd 87 d0 fe 85 ee 31 ff f6 20 0c 68 0b fe
48 00 50 14 00"
))[..549];
assert!(key.validate_tag0(tag0, tag0_gst, prna, navdata_adkd0));
assert!(key.validate_tag0(tag0, tag0_gst, prna, NmaStatus::Test, navdata_adkd0));
}

fn test_mack() -> Mack<'static, NotValidated> {
Expand Down

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