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fix(cryptography): derive HKDF from HMAC for an empty IKM - #11024
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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If this is fixed upstream, we can use react-native-quick-crypto with zero IKM. |
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| // Some WebCrypto implementations, such as react-native-quick-crypto, reject | ||
| // an empty HKDF key, so derive it from HMAC as RFC 5869 defines it. |
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Since this seems like a bug in react-native-quick-crypto, where it doesn't conform to the spec and I have verified that our existing implementation works in both Node.js and the browser I think we should prefer upstreaming a fix. @matthiasgeihs has already opened a PR for this.
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Related PR that bumps react-native-quick-crypto on mobile.
MetaMask/metamask-mobile#38279
Once that's in, we might be able to drop this one here.
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Extracts the real MPC money keyring from feat/money-mfa-mpc-account without the Money MFA UI or 2FA approval path: - `buildRealMpcMoneyKeyringBuilder`: DKLS23/CL24 via `@metamask/mpc-react-native`, dev MPC service endpoints, pinned MFA whitelist config, placeholder backup key. Registered in `getKeyringBuilders` under `MM_MONEY_MPC_REAL_KEYRING` (needs `MM_MONEY_MPC_KEYRING_ENABLED`). - `empty-ikm-hkdf-workaround`: lets `crypto.subtle` run the HKDF with an empty IKM that the Noise `Split` in `@metamask/mfa-wallet-network` needs and `react-native-quick-crypto` rejects. Temporary until MetaMask/core#11024 and MetaMask/mfa-wallet-sdk#68. - Developer-options section that creates the MPC money account via `MoneyAccountController.createMoneyAccount({ type: 'mpc' })` and signs and recovers a test message. - Adds `@metamask/mpc-react-native` and pins `uniffi-bindgen-react-native`; transpiles the ESM-only TSS packages in jest; maps `@metamask/eth-money-mpc-keyring/v2` types in tsconfig.
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Explanation
The bug
hkdfSha256/hkdfSha384/hkdfSha512import the IKM as a WebCrypto HKDF key. On React Native,react-native-quick-cryptorejects an empty HKDF key (HKDF derivation failed), even withunsafeInputKeyingMaterial: true. Browsers and Node accept it.When it happens
Any HKDF call with an empty IKM on React Native. The Noise
Splitstep always does this (the Noise spec definesSplitasHKDF(ck, zerolen)), so every Noise handshake in@metamask/mfa-wallet-networkfails on mobile. That blocks MPC key creation for the Money account (@metamask/eth-money-mpc-keyring+@metamask/mpc-react-native), which surfaces asCl24Error: Rust panic.The fix
When the IKM is empty, compute HKDF from WebCrypto HMAC using the Extract and Expand steps of RFC 5869 (an empty salt becomes
HashLenzero bytes). Non-empty IKM still uses WebCrypto HKDF. The output is the same as WebCrypto HKDF for the same inputs. No new dependencies.References
Splitpasses a chaining key that is zeroed while HKDF is running. This path reads it before it is zeroed, so keys would not match peers that read it after.Testing
crypto.hkdfSyncfor SHA-256/384/512, an empty salt, info, and multi-block lengths; the 255-block limit throws.Checklist