sp_core/
proof_of_possession.rs

1// This file is part of Substrate.
2
3// Copyright (C) Parity Technologies (UK) Ltd.
4// SPDX-License-Identifier: Apache-2.0
5
6// Licensed under the Apache License, Version 2.0 (the "License");
7// you may not use this file except in compliance with the License.
8// You may obtain a copy of the License at
9//
10// 	http://www.apache.org/licenses/LICENSE-2.0
11//
12// Unless required by applicable law or agreed to in writing, software
13// distributed under the License is distributed on an "AS IS" BASIS,
14// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15// See the License for the specific language governing permissions and
16// limitations under the License.
17
18//! Utilities for proving possession of a particular public key
19
20use crate::crypto::{CryptoType, Pair};
21use sp_std::vec::Vec;
22
23/// Pair which is able to generate proof of possession.
24///
25/// This is implemented in different trait to provide default behavior.
26pub trait ProofOfPossessionGenerator: Pair
27where
28	Self::Public: CryptoType,
29{
30	/// Generate proof of possession.
31	///
32	/// The proof of possession generator is supposed to
33	/// produce a "signature" with unique hash context that should
34	/// never be used in other signatures. This proves that
35	/// the secret key is known to the prover. While prevent
36	/// malicious actors to trick an honest party to sign an
37	/// unpossessed public key resulting in a rogue key attack (See: Section 4.3 of
38	/// - Ristenpart, T., & Yilek, S. (2007). The power of proofs-of-possession: Securing multiparty
39	///   signatures against rogue-key attacks. In , Annual {{International Conference}} on the
40	///   {{Theory}} and {{Applications}} of {{Cryptographic Techniques} (pp. 228–245). : Springer).
41	#[cfg(feature = "full_crypto")]
42	fn generate_proof_of_possession(&mut self) -> Self::Signature;
43}
44
45/// Pair which is able to verify proof of possession.
46///
47/// While you don't need a keypair to verify a proof of possession (you only need a public key)
48/// we constrain on Pair to use the Public and Signature types associated to Pair.
49/// This is implemented in different trait (than Public Key) to provide default behavior.
50pub trait ProofOfPossessionVerifier: Pair
51where
52	Self::Public: CryptoType,
53{
54	/// Verify proof of possession.
55	///
56	/// The proof of possession verifier is supposed to to verify a signature with unique hash
57	/// context that is produced solely for this reason. This proves that that the secret key is
58	/// known to the prover.
59	fn verify_proof_of_possession(
60		proof_of_possession: &Self::Signature,
61		allegedly_possessesd_pubkey: &Self::Public,
62	) -> bool;
63}
64
65/// Marker trait to identify whether the scheme is not aggregatable.
66///
67/// Aggregatable schemes may change/optimize implementation parts such as Proof Of Possession
68/// or other specifics.
69///
70/// This is specifically because implementation of proof of possession for aggregatable schemes
71/// is security critical.
72///
73/// We would like to prevent aggregatable scheme from unknowingly generating signatures
74/// which aggregate to false albeit valid proof of possession aka rogue key attack.
75/// We ensure that by separating signing and generating proof_of_possession at the API level.
76///
77/// Rogue key attack however is not immediately applicable to non-aggregatable scheme
78/// when even if an honest signing oracle is tricked to sign a rogue proof_of_possession, it is not
79/// possible to aggregate it to generate a valid proof for a key the attack does not
80/// possess. Therefore we do not require non-aggregatable schemes to prevent proof_of_possession
81/// confirming signatures at API level
82pub trait NonAggregatable: Pair {
83	/// Default proof_of_possession statement.
84	fn proof_of_possession_statement(pk: &impl crate::Public) -> Vec<u8> {
85		/// The context which attached to pop message to attest its purpose.
86		const PROOF_OF_POSSESSION_CONTEXT_TAG: &[u8; 4] = b"POP_";
87		[PROOF_OF_POSSESSION_CONTEXT_TAG, pk.to_raw_vec().as_slice()].concat()
88	}
89}
90
91impl<T> ProofOfPossessionVerifier for T
92where
93	T: NonAggregatable,
94{
95	/// Default implementation for non-aggregatable signatures.
96	///
97	/// While we enforce hash context separation at the library level in aggregatable schemes,
98	/// it remains as an advisory for the default implementation using signature API used for
99	/// non-aggregatable schemes
100	fn verify_proof_of_possession(
101		proof_of_possession: &Self::Signature,
102		allegedly_possessesd_pubkey: &Self::Public,
103	) -> bool {
104		let proof_of_possession_statement =
105			Self::proof_of_possession_statement(allegedly_possessesd_pubkey);
106		Self::verify(
107			&proof_of_possession,
108			proof_of_possession_statement,
109			allegedly_possessesd_pubkey,
110		)
111	}
112}
113
114impl<T> ProofOfPossessionGenerator for T
115where
116	T: NonAggregatable,
117{
118	/// Default implementation for non-aggregatable signatures.
119	///
120	/// While we enforce hash context separation at the library level in aggregatable schemes,
121	/// it remains as an advisory for the default implementation using signature API used for
122	/// non-aggregatable schemes
123	#[cfg(feature = "full_crypto")]
124	fn generate_proof_of_possession(&mut self) -> Self::Signature {
125		let proof_of_possession_statement = Self::proof_of_possession_statement(&self.public());
126		self.sign(proof_of_possession_statement.as_slice())
127	}
128}
sp_core/proof_of_possession.rs

sp_core/
proof_of_possession.rs
