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Add PaymentId authentication to public API #3242

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Merged
merged 2 commits into from
Aug 19, 2024
Merged

Add PaymentId authentication to public API #3242

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fa6c058
Return a Result from verify_payment_id
jkczyz Aug 16, 2024
5bee20e
Add PaymentId authentication to public API
jkczyz Aug 14, 2024
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21 changes: 19 additions & 2 deletions lightning/src/ln/channelmanager.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@ use bitcoin::key::constants::SECRET_KEY_SIZE;
use bitcoin::network::Network;

use bitcoin::hashes::Hash;
use bitcoin::hashes::hmac::Hmac;
use bitcoin::hashes::sha256::Hash as Sha256;
use bitcoin::hash_types::{BlockHash, Txid};

Expand Down Expand Up @@ -413,6 +414,22 @@ pub struct PaymentId(pub [u8; Self::LENGTH]);
impl PaymentId {
/// Number of bytes in the id.
pub const LENGTH: usize = 32;

/// Constructs an HMAC to include in [`OffersContext::OutboundPayment`] for the payment id
/// along with the given [`Nonce`].
pub fn hmac_for_offer_payment(
&self, nonce: Nonce, expanded_key: &inbound_payment::ExpandedKey,
) -> Hmac<Sha256> {
signer::hmac_for_payment_id(*self, nonce, expanded_key)
}

/// Authenticates the payment id using an HMAC and a [`Nonce`] taken from an
/// [`OffersContext::OutboundPayment`].
pub fn verify(
&self, hmac: Hmac<Sha256>, nonce: Nonce, expanded_key: &inbound_payment::ExpandedKey,
) -> Result<(), ()> {
signer::verify_payment_id(*self, hmac, nonce, expanded_key)
}
}

impl Writeable for PaymentId {
Expand Down Expand Up @@ -9024,7 +9041,7 @@ where
};
let invoice_request = builder.build_and_sign()?;

let hmac = signer::hmac_for_payment_id(payment_id, nonce, expanded_key);
let hmac = payment_id.hmac_for_offer_payment(nonce, expanded_key);
let context = OffersContext::OutboundPayment { payment_id, nonce, hmac: Some(hmac) };
let reply_paths = self.create_blinded_paths(context)
.map_err(|_| Bolt12SemanticError::MissingPaths)?;
Expand Down Expand Up @@ -10900,7 +10917,7 @@ where

match context {
Some(OffersContext::OutboundPayment { payment_id, nonce, hmac: Some(hmac) }) => {
if signer::verify_payment_id(payment_id, hmac, nonce, expanded_key) {
if let Ok(()) = payment_id.verify(hmac, nonce, expanded_key) {
self.abandon_payment_with_reason(
payment_id, PaymentFailureReason::InvoiceRequestRejected,
);
Expand Down
4 changes: 2 additions & 2 deletions lightning/src/offers/signer.rs
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Expand Up @@ -410,6 +410,6 @@ pub(crate) fn hmac_for_payment_id(

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@valentinewallace valentinewallace Aug 16, 2024

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Re: hmac_for_offer call above -- it looks like ExpandedKey::hmac_for_offer docs need an update since it is only supposed to be used to construct offer metadata atm. It almost looks like we should have used a new key for InvoiceError verification, though I might be missing a prior discussion.

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@jkczyz jkczyz Aug 16, 2024

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Right, we are using it for both offer metadata and payer metadata. I think we were fine with this because we add different inputs for each use case. @TheBlueMatt Is that correct?

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@TheBlueMatt TheBlueMatt Aug 19, 2024

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Yea, we use a different IV (which is always in the same position in the data being hashed) so its fine.

pub(crate) fn verify_payment_id(
payment_id: PaymentId, hmac: Hmac<Sha256>, nonce: Nonce, expanded_key: &ExpandedKey,
) -> bool {
hmac_for_payment_id(payment_id, nonce, expanded_key) == hmac
) -> Result<(), ()> {
if hmac_for_payment_id(payment_id, nonce, expanded_key) == hmac { Ok(()) } else { Err(()) }
}