core_crypto/mls/conversation/
config.rs

1//! Conversation configuration.
2//!
3//! Either use [MlsConversationConfiguration] when creating a conversation or [MlsCustomConfiguration]
4//! when joining one by Welcome or external commit
5
6use mls_crypto_provider::MlsCryptoProvider;
7use openmls::prelude::{
8    Capabilities, Credential, CredentialType, ExternalSender, OpenMlsSignaturePublicKey,
9    PURE_CIPHERTEXT_WIRE_FORMAT_POLICY, PURE_PLAINTEXT_WIRE_FORMAT_POLICY, ProtocolVersion,
10    RequiredCapabilitiesExtension, SenderRatchetConfiguration, WireFormatPolicy,
11};
12use openmls_traits::{
13    OpenMlsCryptoProvider,
14    crypto::OpenMlsCrypto,
15    types::{Ciphersuite, SignatureScheme},
16};
17use serde::{Deserialize, Serialize};
18use wire_e2e_identity::prelude::parse_json_jwk;
19
20use super::Result;
21use crate::{MlsError, RecursiveError, prelude::MlsCiphersuite};
22
23/// Sets the config in OpenMls for the oldest possible epoch(past current) that a message can be decrypted
24pub(crate) const MAX_PAST_EPOCHS: usize = 3;
25
26/// Window for which decryption secrets are kept within an epoch. Use this with caution since this affects forward secrecy within an epoch.
27/// Use this when the Delivery Service cannot guarantee application messages order
28pub(crate) const OUT_OF_ORDER_TOLERANCE: u32 = 2;
29
30/// How many application messages can be skipped. Use this when the Delivery Service can drop application messages
31pub(crate) const MAXIMUM_FORWARD_DISTANCE: u32 = 1000;
32
33/// The configuration parameters for a group/conversation
34#[derive(Debug, Clone, Default)]
35pub struct MlsConversationConfiguration {
36    /// The `OpenMls` Ciphersuite used in the group
37    pub ciphersuite: MlsCiphersuite,
38    /// Delivery service public signature key and credential
39    pub external_senders: Vec<ExternalSender>,
40    /// Implementation specific configuration
41    pub custom: MlsCustomConfiguration,
42}
43
44impl MlsConversationConfiguration {
45    const WIRE_SERVER_IDENTITY: &'static str = "wire-server";
46
47    const PADDING_SIZE: usize = 128;
48
49    /// Default protocol
50    pub(crate) const DEFAULT_PROTOCOL_VERSION: ProtocolVersion = ProtocolVersion::Mls10;
51
52    /// List all until further notice
53    pub(crate) const DEFAULT_SUPPORTED_CREDENTIALS: &'static [CredentialType] =
54        &[CredentialType::Basic, CredentialType::X509];
55
56    /// Conservative sensible defaults
57    pub(crate) const DEFAULT_SUPPORTED_CIPHERSUITES: &'static [Ciphersuite] = &[
58        Ciphersuite::MLS_128_DHKEMX25519_AES128GCM_SHA256_Ed25519,
59        Ciphersuite::MLS_128_DHKEMP256_AES128GCM_SHA256_P256,
60        Ciphersuite::MLS_128_DHKEMX25519_CHACHA20POLY1305_SHA256_Ed25519,
61        Ciphersuite::MLS_256_DHKEMP384_AES256GCM_SHA384_P384,
62        Ciphersuite::MLS_256_DHKEMP521_AES256GCM_SHA512_P521,
63    ];
64
65    /// Not used at the moment
66    const NUMBER_RESUMPTION_PSK: usize = 1;
67
68    /// Generates an `MlsGroupConfig` from this configuration
69    #[inline(always)]
70    pub fn as_openmls_default_configuration(&self) -> Result<openmls::group::MlsGroupConfig> {
71        let crypto_config = openmls::prelude::CryptoConfig {
72            version: Self::DEFAULT_PROTOCOL_VERSION,
73            ciphersuite: self.ciphersuite.into(),
74        };
75        Ok(openmls::group::MlsGroupConfig::builder()
76            .wire_format_policy(self.custom.wire_policy.into())
77            .max_past_epochs(MAX_PAST_EPOCHS)
78            .padding_size(Self::PADDING_SIZE)
79            .number_of_resumption_psks(Self::NUMBER_RESUMPTION_PSK)
80            .leaf_capabilities(Self::default_leaf_capabilities())
81            .required_capabilities(self.default_required_capabilities())
82            .sender_ratchet_configuration(SenderRatchetConfiguration::new(
83                self.custom.out_of_order_tolerance,
84                self.custom.maximum_forward_distance,
85            ))
86            .use_ratchet_tree_extension(true)
87            .external_senders(self.external_senders.clone())
88            .crypto_config(crypto_config)
89            .build())
90    }
91
92    /// Default capabilities for every generated [openmls::prelude::KeyPackage]
93    pub fn default_leaf_capabilities() -> Capabilities {
94        Capabilities::new(
95            Some(&[Self::DEFAULT_PROTOCOL_VERSION]),
96            Some(Self::DEFAULT_SUPPORTED_CIPHERSUITES),
97            Some(&[]),
98            Some(&[]),
99            Some(Self::DEFAULT_SUPPORTED_CREDENTIALS),
100        )
101    }
102
103    fn default_required_capabilities(&self) -> RequiredCapabilitiesExtension {
104        RequiredCapabilitiesExtension::new(&[], &[], Self::DEFAULT_SUPPORTED_CREDENTIALS)
105    }
106
107    /// This expects a raw json serialized JWK. It works with any Signature scheme
108    pub(crate) fn parse_external_sender(jwk: &[u8]) -> Result<ExternalSender> {
109        let pk = parse_json_jwk(jwk)
110            .map_err(wire_e2e_identity::prelude::E2eIdentityError::from)
111            .map_err(crate::e2e_identity::Error::from)
112            .map_err(RecursiveError::e2e_identity("parsing jwk"))?;
113        Ok(ExternalSender::new(
114            pk.into(),
115            Credential::new_basic(Self::WIRE_SERVER_IDENTITY.into()),
116        ))
117    }
118
119    /// This supports the legacy behaviour where the server was providing the external sender public key
120    /// raw.
121    // TODO: remove at some point when the backend API is not used anymore. Tracking issue: WPB-9614
122    pub(crate) fn legacy_external_sender(
123        key: Vec<u8>,
124        signature_scheme: SignatureScheme,
125        backend: &MlsCryptoProvider,
126    ) -> Result<ExternalSender> {
127        backend
128            .crypto()
129            .validate_signature_key(signature_scheme, &key[..])
130            .map_err(MlsError::wrap("validating signature key"))?;
131        let key = OpenMlsSignaturePublicKey::new(key.into(), signature_scheme)
132            .map_err(MlsError::wrap("creating new signature public key"))?;
133        Ok(ExternalSender::new(
134            key.into(),
135            Credential::new_basic(Self::WIRE_SERVER_IDENTITY.into()),
136        ))
137    }
138}
139
140/// The configuration parameters for a group/conversation which are not handled natively by openmls
141#[derive(Debug, Clone, Serialize, Deserialize)]
142pub struct MlsCustomConfiguration {
143    // TODO: Not implemented yet. Tracking issue: WPB-9609
144    /// Duration in seconds after which we will automatically force a self_update commit
145    pub key_rotation_span: Option<std::time::Duration>,
146    /// Defines if handshake messages are encrypted or not
147    pub wire_policy: MlsWirePolicy,
148    /// Window for which decryption secrets are kept within an epoch. Use this with caution since
149    /// this affects forward secrecy within an epoch. Use this when the Delivery Service cannot
150    /// guarantee application messages order.
151    pub out_of_order_tolerance: u32,
152    /// How many application messages can be skipped. Use this when the Delivery Service can drop
153    /// application messages
154    pub maximum_forward_distance: u32,
155}
156
157impl Default for MlsCustomConfiguration {
158    fn default() -> Self {
159        Self {
160            wire_policy: MlsWirePolicy::Plaintext,
161            key_rotation_span: Default::default(),
162            out_of_order_tolerance: OUT_OF_ORDER_TOLERANCE,
163            maximum_forward_distance: MAXIMUM_FORWARD_DISTANCE,
164        }
165    }
166}
167
168/// Wrapper over [WireFormatPolicy](openmls::prelude::WireFormatPolicy)
169#[derive(Debug, Copy, Clone, Default, Eq, PartialEq, Serialize, Deserialize)]
170#[repr(u8)]
171pub enum MlsWirePolicy {
172    /// Handshake messages are never encrypted
173    #[default]
174    Plaintext = 1,
175    /// Handshake messages are always encrypted
176    Ciphertext = 2,
177}
178
179impl From<MlsWirePolicy> for WireFormatPolicy {
180    fn from(policy: MlsWirePolicy) -> Self {
181        match policy {
182            MlsWirePolicy::Ciphertext => PURE_CIPHERTEXT_WIRE_FORMAT_POLICY,
183            MlsWirePolicy::Plaintext => PURE_PLAINTEXT_WIRE_FORMAT_POLICY,
184        }
185    }
186}
187
188#[cfg(test)]
189mod tests {
190    use openmls::prelude::ProtocolVersion;
191    use openmls_traits::{
192        OpenMlsCryptoProvider,
193        crypto::OpenMlsCrypto,
194        types::{SignatureScheme, VerifiableCiphersuite},
195    };
196    use wasm_bindgen_test::*;
197    use wire_e2e_identity::prelude::JwsAlgorithm;
198
199    use crate::mls::conversation::ConversationWithMls as _;
200    use crate::{prelude::MlsConversationConfiguration, test_utils::*};
201
202    wasm_bindgen_test_configure!(run_in_browser);
203
204    #[cfg_attr(not(target_family = "wasm"), async_std::test)]
205    #[wasm_bindgen_test]
206    pub async fn group_should_have_required_capabilities() {
207        let case = TestContext::default();
208
209        let [cc] = case.sessions().await;
210        Box::pin(async move {
211            let id = conversation_id();
212            cc.transaction
213                .new_conversation(&id, case.credential_type, case.cfg.clone())
214                .await
215                .unwrap();
216            let conv = cc.transaction.conversation(&id).await.unwrap();
217            let group = conv.conversation().await;
218
219            let capabilities = group.group.group_context_extensions().required_capabilities().unwrap();
220
221            // see https://www.rfc-editor.org/rfc/rfc9420.html#section-11.1
222            assert!(capabilities.extension_types().is_empty());
223            assert!(capabilities.proposal_types().is_empty());
224            assert_eq!(
225                capabilities.credential_types(),
226                MlsConversationConfiguration::DEFAULT_SUPPORTED_CREDENTIALS
227            );
228        })
229        .await
230    }
231
232    #[apply(all_cred_cipher)]
233    #[wasm_bindgen_test]
234    pub async fn creator_leaf_node_should_have_default_capabilities(case: TestContext) {
235        let [cc] = case.sessions().await;
236        Box::pin(async move {
237            let id = conversation_id();
238            cc.transaction
239                .new_conversation(&id, case.credential_type, case.cfg.clone())
240                .await
241                .unwrap();
242            let conv = cc.transaction.conversation(&id).await.unwrap();
243            let group = conv.conversation().await;
244
245            // verifying https://www.rfc-editor.org/rfc/rfc9420.html#section-7.2
246            let creator_capabilities = group.group.own_leaf().unwrap().capabilities();
247
248            // https://www.rfc-editor.org/rfc/rfc9420.html#section-7.2-5.1.1
249            // ProtocolVersion must be the default one
250            assert_eq!(creator_capabilities.versions(), &[ProtocolVersion::Mls10]);
251
252            // To prevent downgrade attacks, Ciphersuite MUST ONLY contain the current one
253            assert_eq!(
254                creator_capabilities.ciphersuites().to_vec(),
255                MlsConversationConfiguration::DEFAULT_SUPPORTED_CIPHERSUITES
256                    .iter()
257                    .map(|c| VerifiableCiphersuite::from(*c))
258                    .collect::<Vec<_>>()
259            );
260
261            // Proposals MUST be empty since we support all the default ones
262            assert!(creator_capabilities.proposals().is_empty());
263
264            // Extensions MUST only contain non-default extension (i.e. empty for now)
265            assert!(creator_capabilities.extensions().is_empty(),);
266
267            // To prevent downgrade attacks, Credentials should just contain the current
268            assert_eq!(
269                creator_capabilities.credentials(),
270                MlsConversationConfiguration::DEFAULT_SUPPORTED_CREDENTIALS
271            );
272        })
273        .await
274    }
275
276    #[apply(all_cred_cipher)]
277    #[wasm_bindgen_test]
278    pub async fn should_support_raw_external_sender(case: TestContext) {
279        let [cc] = case.sessions().await;
280        Box::pin(async move {
281            let (_sk, pk) = cc
282                .transaction
283                .mls_provider()
284                .await
285                .unwrap()
286                .crypto()
287                .signature_key_gen(case.signature_scheme())
288                .unwrap();
289
290            assert!(
291                cc.transaction
292                    .set_raw_external_senders(&mut case.cfg.clone(), vec![pk])
293                    .await
294                    .is_ok()
295            );
296        })
297        .await
298    }
299
300    #[apply(all_cred_cipher)]
301    #[wasm_bindgen_test]
302    pub async fn should_support_jwk_external_sender(case: TestContext) {
303        let [cc] = case.sessions().await;
304        Box::pin(async move {
305            let sc = case.signature_scheme();
306
307            let alg = match sc {
308                SignatureScheme::ED25519 => JwsAlgorithm::Ed25519,
309                SignatureScheme::ECDSA_SECP256R1_SHA256 => JwsAlgorithm::P256,
310                SignatureScheme::ECDSA_SECP384R1_SHA384 => JwsAlgorithm::P384,
311                SignatureScheme::ECDSA_SECP521R1_SHA512 => JwsAlgorithm::P521,
312                SignatureScheme::ED448 => unreachable!(),
313            };
314
315            let jwk = wire_e2e_identity::prelude::generate_jwk(alg);
316            cc.transaction
317                .set_raw_external_senders(&mut case.cfg.clone(), vec![jwk])
318                .await
319                .unwrap();
320        })
321        .await;
322    }
323}
core_crypto/mls/conversation/config.rs

core_crypto/mls/conversation/
config.rs
