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sp_core/
proof_of_possession.rs

1// This file is part of Substrate.
2
3// Copyright (C) Parity Technologies (UK) Ltd.  SPDX-License-Identifier: Apache-2.0
4
5// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
6// in compliance with the License.  You may obtain a copy of the License at
7//
8// 	http://www.apache.org/licenses/LICENSE-2.0
9//
10// Unless required by applicable law or agreed to in writing, software distributed under the License
11// is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
12// or implied.  See the License for the specific language governing permissions and limitations
13// under the License.
14
15//! Utilities for proving possession of a particular public key
16
17use crate::crypto::{CryptoType, Pair, Signature};
18use sp_std::vec::Vec;
19
20/// Pair which is able to generate proof of possession.
21///
22/// This is implemented in different trait to provide default behavior.
23pub trait ProofOfPossessionGenerator: Pair
24where
25	Self::Public: CryptoType,
26	Self::ProofOfPossession: Signature,
27{
28	/// Generate proof of possession.
29	///
30	/// This is usually done by signing the owner's identifier, this is prevent front runner to
31	/// claim ownership of public keys of other entities.
32	///
33	/// However, for aggregatable signature the proof of possession generator is supposed to
34	/// produce a "signature" with unique hash context that should never be used in other
35	/// signatures. While this proves that the secret key is known to the prover, it prevents
36	/// malicious actors to trick an honest party to sign an unpossessed public key resulting in
37	/// a rogue key attack (See: Section 4.3 of - Ristenpart, T., & Yilek, S. (2007). The power
38	/// of proofs-of-possession: Securing multiparty signatures against rogue-key attacks. In ,
39	/// Annual {{International Conference}} on the {{Theory}} and {{Applications}} of
40	/// {{Cryptographic Techniques} (pp. 228–245). : Springer).
41	///
42	/// As such, for aggregatable signatures, proof of possession consists of two signatures one
43	/// regular signature signing the owner identity and the second one with unique context
44	/// which signs the correspoding public key (and nothing else).
45	#[cfg(feature = "full_crypto")]
46	fn generate_proof_of_possession(&mut self, owner: &[u8]) -> Self::ProofOfPossession;
47}
48
49/// Pair which is able to verify proof of possession.
50///
51/// While you don't need a keypair to verify a proof of possession (you only need a public key) we
52/// constrain on Pair to use the Public and Signature types associated to Pair.  This is implemented
53/// in different trait (than Public Key) to provide default behavior.
54pub trait ProofOfPossessionVerifier: Pair
55where
56	Self::Public: CryptoType,
57	Self::ProofOfPossession: Signature,
58{
59	/// Verify proof of possession.
60	///
61	/// The proof of possession verifier is supposed to to verify a signature with unique hash
62	/// context that is produced solely for this reason. This proves that that the secret key is
63	/// known to the prover.
64	fn verify_proof_of_possession(
65		owner: &[u8],
66		proof_of_possession: &Self::ProofOfPossession,
67		allegedly_possessesd_pubkey: &Self::Public,
68	) -> bool;
69}
70
71/// Simply returns the owner prefixed with proof of possession context.
72pub fn statement_of_ownership(owner: &[u8]) -> Vec<u8> {
73	/// The context which attached to pop message to attest its purpose.
74	const PROOF_OF_POSSESSION_CONTEXT_TAG: &[u8; 4] = b"POP_";
75	[PROOF_OF_POSSESSION_CONTEXT_TAG, owner].concat()
76}
77
78/// Marker trait to identify whether the scheme is not aggregatable.
79///
80/// Aggregatable schemes may change/optimize implementation parts such as Proof Of Possession or
81/// other specifics.
82///
83/// This is specifically because implementation of proof of possession for aggregatable schemes is
84/// security critical.
85///
86/// We would like to prevent aggregatable scheme from unknowingly generating signatures which
87/// aggregate to false albeit valid proof of possession aka rogue key attack.  We ensure that by
88/// separating signing and generating proof_of_possession at the API level.
89///
90/// Rogue key attack however is not immediately applicable to non-aggregatable scheme when even if
91/// an honest signing oracle is tricked to sign a rogue proof_of_possession, it is not possible to
92/// aggregate it to generate a valid proof for a key the attack does not possess. Therefore we do
93/// not require non-aggregatable schemes to prevent proof_of_possession confirming signatures at API
94/// level
95pub trait NonAggregatable: Pair {
96	/// Default proof_of_possession statement.
97	fn proof_of_possession_statement(owner: &[u8]) -> Vec<u8> {
98		statement_of_ownership(owner)
99	}
100}
101
102impl<T> ProofOfPossessionVerifier for T
103where
104	T: NonAggregatable<ProofOfPossession = Self::Signature>,
105{
106	/// Default implementation for non-aggregatable signatures.
107	///
108	/// While we enforce hash context separation at the library level in aggregatable schemes,
109	/// it remains as an advisory for the default implementation using signature API used for
110	/// non-aggregatable schemes
111	fn verify_proof_of_possession(
112		owner: &[u8],
113		proof_of_possession: &Self::ProofOfPossession,
114		allegedly_possessesd_pubkey: &Self::Public,
115	) -> bool {
116		let proof_of_possession_statement = statement_of_ownership(owner);
117		Self::verify(
118			&proof_of_possession,
119			proof_of_possession_statement,
120			allegedly_possessesd_pubkey,
121		)
122	}
123}
124
125impl<T> ProofOfPossessionGenerator for T
126where
127	T: NonAggregatable<ProofOfPossession = Self::Signature>,
128{
129	/// Default implementation for non-aggregatable signatures.
130	///
131	/// While we enforce hash context separation at the library level in aggregatable schemes,
132	/// it remains as an advisory for the default implementation using signature API used for
133	/// non-aggregatable schemes
134	#[cfg(feature = "full_crypto")]
135	fn generate_proof_of_possession(&mut self, owner: &[u8]) -> Self::ProofOfPossession {
136		let proof_of_possession_statement = statement_of_ownership(owner);
137		self.sign(proof_of_possession_statement.as_slice())
138	}
139}