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// LNP/BP Core Library implementing LNPBP specifications & standards // Written in 2020 by // Dr. Maxim Orlovsky <orlovsky@pandoracore.com> // // To the extent possible under law, the author(s) have dedicated all // copyright and related and neighboring rights to this software to // the public domain worldwide. This software is distributed without // any warranty. // // You should have received a copy of the MIT License // along with this software. // If not, see <https://opensource.org/licenses/MIT>. use std::collections::BTreeSet; use bitcoin::hashes::{sha256, Hash, HashEngine, Hmac, HmacEngine}; use bitcoin::secp256k1; use crate::SECP256K1; lazy_static! { /// Single SHA256 hash of "LNPBP1" string according to LNPBP-1 acting as a /// prefix to the message in computing tweaking factor pub static ref LNPBP1_HASHED_TAG: [u8; 32] = { sha256::Hash::hash(b"LNPBP1").into_inner() }; } /// Deterministically-organized set of all public keys used by this mod /// internally type Keyset = BTreeSet<secp256k1::PublicKey>; /// Errors that may happen during LNPBP-1 commitment procedure or because of /// incorrect arguments provided to [`commit()`] function. #[derive(Clone, Copy, PartialEq, Eq, Debug, Display, Error, From)] #[display(doc_comments)] pub enum Error { /// Keyset must include target public key, but no target key found it /// the provided set. NotKeysetMember, /// Elliptic curve point addition resulted in point in infinity; you /// must select different source public keys SumInfiniteResult, /// LNPBP-1 commitment either is outside of Secp256k1 order `n` (this event /// has negligible probability <~2^-64), or, when added to the provided /// keyset, results in point at infinity. You may try with a different /// source message or public keys. InvalidTweak, } /// Function performs commitment procedure according to LNPBP-1. /// /// # Parameters /// /// - A set of public keys for committing during the LNPBP-1 procedure /// - Target public key for tweaking. Must be a part of the keyset, otherwise /// function will fail with [`Error::NotKeysetMember`] /// - Protocol-specific tag in form of 32-byte hash /// - Message to commit to, which must be representable as a byte slice using /// [`AsRef::as_ref()`] /// /// # Returns /// /// Function mutates two of its parameters, /// - `target_pubkey`, with a tweaked version of the public key containing /// commitment to the message and the rest of keyset, /// - `keyset`, by replacing original `target_pubkey` with its tweaked version /// and returns `tweaking_factor` as a return parameter wrapped into /// [`Result::Ok`]. /// /// If the function fails with any error, value for `target_pubkey` and `keyset` /// is undefined and must be discarded. /// /// # Errors /// /// Function may fail because of one of the following circumstances: /// - If `target_pubkey` is not a part of `keyset` ([`Error::NotKeysetMember`]) /// - If keyset deliberately constructed in a way that sum of some of its keys /// is equivalent to negation of some other keys. In this case function fails /// with [`Error::SumInfiniteResult`] /// - With negligible probability because of elliptic curve Secp256k1 point /// addition overflow; in this case function returns either /// [`Error::SumInfiniteResult`], if it happens during summation of public /// keys from the `keyset`, or [`Error::InvalidTweak`], if it happens during /// tweaking factor addition to the `target_pubkey`. /// /// # Protocol: /// /// Please refer to the original document for the verification: /// <https://github.com/LNP-BP/LNPBPs/blob/master/lnpbp-0001.md> // #[consensus_critical("RGB")] // #[standard_critical("LNPBP-1")] pub fn commit( keyset: &mut Keyset, target_pubkey: &mut secp256k1::PublicKey, protocol_tag: &sha256::Hash, message: &impl AsRef<[u8]>, ) -> Result<Hmac<sha256::Hash>, Error> { if !keyset.remove(target_pubkey) { return Err(Error::NotKeysetMember); } // ! [CONSENSUS-CRITICAL]: // ! [STANDARD-CRITICAL]: We commit to the sum of all public keys, // not a single pubkey. For single key the set // is represented by itself let pubkey_sum = keyset .iter() .try_fold(target_pubkey.clone(), |sum, pubkey| sum.combine(pubkey)) .map_err(|_| Error::SumInfiniteResult)?; // ! [CONSENSUS-CRITICAL]: // ! [STANDARD-CRITICAL]: HMAC engine is based on sha256 hash let mut hmac_engine = HmacEngine::<sha256::Hash>::new(&pubkey_sum.serialize()); // ! [CONSENSUS-CRITICAL]: // ! [STANDARD-CRITICAL]: Hash process started with consuming first // protocol prefix: single SHA256 hash of // ASCII "LNPBP-1" string. // NB: We use the same hash as in LNPBP-1 so when there is no other // keys involved the commitment would not differ. hmac_engine.input(&LNPBP1_HASHED_TAG[..]); // ! [CONSENSUS-CRITICAL]: // ! [STANDARD-CRITICAL]: The second prefix comes from the upstream // protocol as a part of the container hmac_engine.input(&protocol_tag[..]); // ! [CONSENSUS-CRITICAL]: // ! [STANDARD-CRITICAL]: Next we hash the message. The message must be // prefixed with the protocol-specific prefix: // another single SHA256 hash of protocol name. // However this is not the part of this function, // the function expect that the `msg` is already // properly prefixed hmac_engine.input(&sha256::Hash::hash(message.as_ref())); // Producing tweaking factor let tweaking_factor = Hmac::from_engine(hmac_engine); // Applying tweaking factor to public key target_pubkey .add_exp_assign(&SECP256K1, &tweaking_factor[..]) .map_err(|_| Error::InvalidTweak)?; keyset.insert(target_pubkey.clone()); // Returning tweaked public key Ok(tweaking_factor) } /// Function verifies commitment created according to LNPBP-1. /// /// # Parameters /// /// - `verified_pubkey`: public key containing LNPBP-1 commitment, i.e. the one /// modified by [`commit()`] procedure as its second parameter `target_key` /// - `original_keyset`: set of public keys provided to the [`commit()`] /// procedure. This set must include orignal pubkey specified in the next /// parameter `taget_pubkey` /// - `target_pubkey`: one of public keys included into the original keyset and /// that was provided to the [`commit()`] procedure as `target_pubkey`. This /// must be an original version of public key from the `verified_pubkey` /// parameter before the tweak was applied /// - `protocol_tag`: protocol-specific tag in form of 32-byte hash /// - `message`: message to commit to, which must be representable as a byte /// slice using [`AsRef::as_ref()`] /// /// # Returns /// /// - `true`, if verification succeeds, /// - `false`, if verification fails, indicating that the provided /// `verified_pubkey` is not committed to the data given in the rest of /// function parameters. /// /// # Procedure /// /// Please refer to the original document for the general algotirhm: /// <https://github.com/LNP-BP/LNPBPs/blob/master/lnpbp-0001.md> /// /// Function verifies commitment by running LNPBP-1 commitment procedure once /// again with the provided data as a source data, and comparing the result of /// the commitment to the `verified_pubkey`. If the commitment function fails, /// it means that it was not able to commit with the provided data, meaning that /// the commitment was not created. Thus, we return that verification have not /// passed, and not a error. Verification succeeds if the commitment procedure /// produces public key equivalent to the `verified_pubkey`. pub fn verify( verified_pubkey: secp256k1::PublicKey, original_keyset: &Keyset, mut target_pubkey: secp256k1::PublicKey, protocol_tag: &sha256::Hash, message: &impl AsRef<[u8]>, ) -> bool { match commit( &mut original_keyset.clone(), &mut target_pubkey, protocol_tag, message, ) { // If the commitment function fails, it means that it was not able to // commit with the provided data, meaning that the commitment was not // created. Thus, we return that verification have not passed, and not // a error. Err(_) => return false, // Verification succeeds if the commitment procedure produces public key // equivalent to the verified one Ok(_) => target_pubkey == verified_pubkey, } } #[cfg(test)] mod test { use std::str::FromStr; use super::*; use crate::bp::test::*; use crate::paradigms::commit_verify::test::*; #[test] fn test_lnpbp1_tag() { assert_eq!( sha256::Hash::hash(b"LNPBP1").into_inner(), *LNPBP1_HASHED_TAG ); assert_ne!( sha256::Hash::hash(b"LNPBP2").into_inner(), *LNPBP1_HASHED_TAG ); assert_ne!( sha256::Hash::hash(b"LNPBP-1").into_inner(), *LNPBP1_HASHED_TAG ); assert_ne!( sha256::Hash::hash(b"LNPBP_1").into_inner(), *LNPBP1_HASHED_TAG ); assert_ne!( sha256::Hash::hash(b"lnpbp1").into_inner(), *LNPBP1_HASHED_TAG ); assert_ne!( sha256::Hash::hash(b"lnpbp-1").into_inner(), *LNPBP1_HASHED_TAG ); assert_ne!( sha256::Hash::hash(b"lnpbp_1").into_inner(), *LNPBP1_HASHED_TAG ); } #[test] fn test_single_key() { let tag = sha256::Hash::hash(b"ProtoTag"); let tag2 = sha256::Hash::hash(b"Prototag"); let messages = gen_messages(); let all_keys = gen_secp_pubkeys(6); let other_key = all_keys[0]; for msg in &messages { for mut pk in all_keys[1..].to_vec() { let original = pk.clone(); let mut keyset = bset![pk]; let mut keyset2 = bset![pk]; let mut pk2 = pk.clone(); let factor1 = commit(&mut keyset, &mut pk, &tag, &msg).unwrap(); let factor2 = commit(&mut keyset2, &mut pk2, &tag2, &msg).unwrap(); // Ensure that changing tag changes commitment and tweaking // factor (and tag is case-sensitive!) assert_ne!(factor1, factor2); assert_ne!(pk, pk2); // Ensure that factor value is not trivial assert_ne!(factor1, Hmac::from_slice(&[0u8; 32]).unwrap()); assert_ne!(factor1, Hmac::from_slice(&[1u8; 32]).unwrap()); assert_ne!(factor1, Hmac::from_slice(&[0xFFu8; 32]).unwrap()); assert_ne!(&factor1[..], &tag[..]); assert_ne!(&factor1[..], &msg[..]); // Verify that the key was indeed tweaked assert_ne!(pk, original); // Verify that the set updated assert_ne!(bset![original], keyset); assert_eq!(bset![pk], keyset); // Do commitment by hand let mut engine = HmacEngine::<sha256::Hash>::new(&original.serialize()); engine.input(&*LNPBP1_HASHED_TAG); engine.input(&tag.into_inner()); engine.input(&sha256::Hash::hash(msg)); let hmac = Hmac::from_engine(engine); let tweaking_factor = *hmac.as_inner(); let mut altkey = original; altkey .add_exp_assign(&SECP256K1, &tweaking_factor[..]) .unwrap(); assert_eq!(altkey, pk); // Now try commitment with a different key, but the same data if other_key != original { let mut other_commitment = other_key; let mut other_keyset = bset![other_commitment]; let factor3 = commit( &mut other_keyset, &mut other_commitment, &tag, &msg, ) .unwrap(); // Make sure we commit to the key value assert_ne!(factor1, factor3); // Make sure commitment value is not the same assert_ne!(pk, other_commitment); // Make sure we can't cross-verify assert_eq!( verify( other_commitment, &bset![original], original, &tag, &msg ), false ); } // Verify commitment assert!(verify(pk, &bset![original], original, &tag, &msg)); // Make sure we can't cross-verify with different tag assert_eq!( verify(pk, &bset![original], original, &tag2, &msg), false ); // Make sure we can't cross-verify with different message assert_eq!( verify( pk, &bset![original], original, &tag2, &b"some other message" ), false ); } } } #[test] fn test_keyset() { let tag = sha256::Hash::hash(b"ProtoTag"); let tag2 = sha256::Hash::hash(b"Prototag"); let messages = gen_messages(); let all_keys = gen_secp_pubkeys(6); let other_key = all_keys[0]; let original_keyset: BTreeSet<_> = all_keys[1..].to_vec().into_iter().collect(); for msg in &messages { for mut pk in original_keyset.clone() { let original = pk.clone(); let mut keyset = original_keyset.clone(); let mut keyset2 = original_keyset.clone(); let mut pk2 = pk.clone(); let factor1 = commit(&mut keyset, &mut pk, &tag, &msg).unwrap(); let factor2 = commit(&mut keyset2, &mut pk2, &tag2, &msg).unwrap(); // Ensure that changing tag changes commitment and tweaking // factor (and tag is case-sensitive!) assert_ne!(factor1, factor2); assert_ne!(pk, pk2); // Ensure that factor value is not trivial assert_ne!(factor1, Hmac::from_slice(&[0u8; 32]).unwrap()); assert_ne!(factor1, Hmac::from_slice(&[1u8; 32]).unwrap()); assert_ne!(factor1, Hmac::from_slice(&[0xFFu8; 32]).unwrap()); assert_ne!(&factor1[..], &tag[..]); assert_ne!(&factor1[..], &msg[..]); // Verify that the key was indeed tweaked assert_ne!(pk, original); // Verify that the set updated assert_ne!(original_keyset.clone(), keyset); // ... but only original key is touched let mut set = keyset.clone(); set.remove(&pk); set.insert(original); assert_eq!(set, original_keyset); // Do commitment by hand let mut engine = HmacEngine::<sha256::Hash>::new(&original.serialize()); engine.input(&*LNPBP1_HASHED_TAG); engine.input(&tag.into_inner()); engine.input(msg); let hmac = Hmac::from_engine(engine); let tweaking_factor = *hmac.as_inner(); let mut altkey = original; altkey .add_exp_assign(&SECP256K1, &tweaking_factor[..]) .unwrap(); // It must not match because done with a single key, not // their sum assert_ne!(altkey, pk); // Now try commitment with a different key, but the same // data if other_key != original { let mut other_pk = other_key; let mut other_keyset = original_keyset.clone(); assert!(!other_keyset.contains(&other_pk)); other_keyset.remove(&pk); other_keyset.insert(other_pk); let factor3 = commit(&mut other_keyset, &mut other_pk, &tag, &msg) .unwrap(); // Make sure we commit to the key value assert_ne!(factor1, factor3); // Make sure commitment value is not the same assert_ne!(pk, other_pk); // Make sure we can't cross-verify assert_eq!( verify( other_pk, &bset![original], original, &tag, &msg ), false ); assert_eq!( verify( other_pk, &original_keyset, original, &tag, &msg ), false ); } // Verify commitment assert!(verify(pk, &original_keyset, original, &tag, &msg)); // Make sure we can't cross-verify with a single key in a set assert_eq!( verify(pk, &bset![original], original, &tag, &msg), false ); // Make sure we can't cross-verify with different tag assert_eq!( verify(pk, &original_keyset, original, &tag2, &msg), false ); // Make sure we can't cross-verify with different message assert_eq!( verify( pk, &original_keyset, original, &tag2, &b"some other message" ), false ); } } } #[test] #[should_panic(expected = "NotKeysetMember")] fn test_failure_not_in_keyset() { let tag = sha256::Hash::hash(b"ProtoTag"); let all_keys = gen_secp_pubkeys(6); let mut pk = all_keys[0]; let mut keyset: BTreeSet<_> = all_keys[1..].to_vec().into_iter().collect(); let _ = commit(&mut keyset, &mut pk, &tag, b"Message").unwrap(); } #[test] #[should_panic(expected = "SumInfiniteResult")] fn test_crafted_negation() { let tag = sha256::Hash::hash(b"ProtoTag"); let mut pubkey = secp256k1::PublicKey::from_str( "0218845781f631c48f1c9709e23092067d06837f30aa0cd0544ac887fe91ddd166", ) .unwrap(); let negkey = secp256k1::PublicKey::from_str( "0318845781f631c48f1c9709e23092067d06837f30aa0cd0544ac887fe91ddd166", ) .unwrap(); let mut keyset = bset![pubkey, negkey]; let _ = commit(&mut keyset, &mut pubkey, &tag, b"Message").unwrap(); } }