Release Notes

CoreCrypto 10

Unreleased

• Reworked E2EI
• New Database API
• New PKI Environment API
• New Credential API
• TS-Native library (dropped the non-persistent wasm client support for non-browser contexts)
• Reworked client id constructor to take typed data instead of a byte string

CoreCrypto 9

v9.3.4 - 2026-04-30

Fixes an issue that could cause epoch observer events to be emitted for epoch changes that would not (yet) actually be persisted to the CoreCrypto database. This is relevant if the CoreCrypto instance is used inside the event handler of the epoch observer (e.g., to update the exported secret). If you created a CoreCrypto transaction inside the handler and didn’t use the CoreCrypto instance directly, this fix is irrelevant.

v9.3.3 - 2026-03-31

• no more errors when deleting a non-existent credential

v9.3.2 - 2026-03-18

• serialize structs into camelCase

v9.3.1 - 2026-03-18

Fixes an enum representation bug on web.

v9.3.0 - 2026-02-20

Lidl compat: Ios and Android can now export a compacted version of the CC database, retaining its encryption. This is only relevant for Lidl builds and should be ignored by everyone else.

v9.2.1 - 2026-02-17

Upgrades openssl to version 3.5.5 (used on Android and iOS for encryption at rest).

v9.2.0 - 2026-02-05

Kotlin changes:

• expose the enitre read-only API on the CoreCrypto type. This allows performing arbitrary read-only operations on data while a transaction is running (e.g., in an EpochObserver event).

• Introduce KotlinInstant type

v9.1.3 - 2025-12-18

Upgrades the binding generator (uniffi 0.29.5) to include a crash fix for Android

v9.1.2 - 2025-11-05

This release fixes a bug in the TypeScript bindings where the commit delay could in some situations be undefined when receiving a proposal.

v9.1.1 - 2025-10-24

This release fixes the issue where libcore_crypto_ffi.so had segments aligned on 4k instead of 16k on Android platforms.

v9.1.0 - 2025-09-29

Note

Even though this is a minor version bump, it contains a breaking change. See below for more information.

• added typescript structured errors
• fix the message rejected reason not being propagated on web
• improvements to logs when epochs advance

Features

• Web: structural errors

  Example Usage

  Extract the abort reason given via an MlsTransportResponse

  try {
      // send a commit that is rejected by the DS
  } catch (err) {
    if(isMlsMessageRejectedError(err)) {
      const rejectReason = err.context.context.reason;
      // other things you want to do with this error...
    } else {
        // log error
    }
  }
  

  Extract the proteus error code

  try {
      // look for a proteus session that doesn't exist
  } catch (err) {
    if(isProteusSessionNotFoundError(err)) {
      const errorCode = err.context.context.errorCode;
      // other things you want to do with this error...
    } else {
        // log error
    }
  }
  

Bug Fixes

• Web: fixed the abort reason of an MlsTransportResponse not being forwarded to rust.

Breaking Changes

• proteusErrorCode field was removed from the root error type, you can get it from the nested context now (see above). Affected platforms: web

v9.0.1 - 2025-09-18

Breaking Changes

• v9.0.0 had erroneously renamed migrateDatabaseKeyTypeToBytes to migrateDbKeyTypeToBytes. This has been fixed, and migrateDatabaseKeyTypeToBytes is usable again on all platforms.

  Affected platforms: Android

Bug Fixes

• Kotlin documentation is now correctly generated and deployed.

v9.0.0 - 2025-09-16

• we’re now tying the Kotlin wrapper more closely to the generated bindings which allows for greater velocity when making changes in code that affects our API - this causes most of the breaking changes in this release
• removed cryptobox migration API
• in Swift, added protection against concurrent access from multiple core crypto instances
• added implicit obfuscation of sensitive data in logs
• reworked the entire build system and CI

Note

In this release we include a fix for missing artifacts in our Web release. The faulty release process affects all 8.x versions. Therefore, instead of migrating from any version < 8.x to 8.x, directly migrate to this version.

Breaking Changes

• Removed support for migrating CoreCrypto database to version 1.

  Affected platforms: Web

  Databases saved by CoreCrypto versions older than 2.0 cannot be migrated anymore.

• Removed proteusCryptoboxMigrate.

  Affected platforms: all

  Support for Cryptobox migration has been removed.

  Migration: remove all calls to proteusCryptoboxMigrate.

• Renamed CoreCryptoContext.proteusDecrypt to CoreCryptoContext.proteusDecryptSafe(...).

  Affected platforms: Android

  It used to be the case that the Kotlin bindings hid the actual behavior of proteusDecrypt by adding a higher-level behavior, trading away some efficiency for ease-of-use. With this change, we have exposed the low-level behavior of proteusDecrypt, enabling for more efficient uses when decrypting many proteus messages at once. The old higher-level behavior of proteusDecrypt is now exposed as proteusDecryptSafe.

  Migration: replace all calls to proteusDecrypt with calls to proteusDecryptSafe.

• Eliminated wrapper class E2EIEnrollment in favor of generated class E2eiEnrollment.

  Affected platforms: Android

  We’ve brought the uniffi-generated code to very near parity with the older high-level bindings. The following breaking changes were necessary to eliminate the old binding class:

  Name changes:

  These methods have had their names changed. To migrate, simply rename all calls to these functions.

  • accountResponse -> newAccountResponse
  • authzResponse -> newAuthzResponse
  • dpopChallengeResponse -> newDpopChallengeResponse
  • contextOidcChallengeResponse -> newOidcChallengeResponse

• Eliminated (hand-written) wrapper class CoreCryptoContext in favor of (uniffi-generated) class CoreCryptoContext.

  Affected platforms: Android

  We’ve brought the uniffi-generated code to very near parity with the older high-level bindings. The following breaking changes were necessar to eliminate the old binding class:

  Name changes:

  These methods have had their names changed. To migrate, simply rename all calls to these functions.

  • getPublicKey -> clientPublicKey
  • generateKeyPackages -> clientKeypackages
  • validKeyPackageCount -> clientValidKeypackagesCount
  • addMember -> addClientsToConversation
  • removeMember -> removeClientsFromConversation
  • members -> getClientIds
  • deriveAvsSecret -> exportSecretKey
  • proteusGetLocalFingerprint -> proteusFingerprint
  • proteusGetRemoteFingerprint -> proteusFingerprintRemote
  • proteusGetPrekeyFingerprint -> proteusFingerprintPrekeyBundle
  • proteusDoesSessionExist -> proteusSessionExists
  • proteusCreateSession -> proteusSessionFromPrekey
  • proteusDeleteSession -> proteusSessionDelete

  Parameter order changes:

  These methods have had the order of their parameters changed. To migrate, either name the arguments in the caller or reorder the parameters appropriately.

  • generateKeyPackages / clientKeypackages: amount is now the final parameter, not the first
  • joinByExternalCommit: credentialType and configuration have swapped positions
  • e2eiNewEnrollment: team now appears after handle and before expirySec
  • e2eiNewActivationEnrollment: team now appears after handle and before expirySec
  • e2eiNewRotateEnrollment: new param order: (displayName, handle, team, expirySec, ciphersuite)
  • proteusCreateSession / proteusSessionFromPrekey: params swapped
  • proteusDecrypt: params swapped
  • proteusEncrypt: params swapped

  Other Parameter changes:

  These methods have had the set of their parameters changed. To migrate, see instructions for each changed method.

  • createConversation: accepts (ConversationId, CredentialType, ConversationConfiguration). Conversation configuration must be constructed externally.

  Removed Methods:

  These methods no longer exist.

  • proteusNewPrekeys: similar to from.until(from + count).map { cc.proteusNewPrekey(it.toUShort()) }
  • proteusNewLastPrekey: similar to cc.proteusLastResortPrekey()
  • proteusEncryptWithPreKey: similar to:

    cc.proteusSessionFromPrekey(sessionId, preKey)
    val encryptedMessage = cc.proteusEncrypt(sessionId, message)
    cc.proteusSessionSave(sessionId)
    return encryptedMessage
    

• Stopped duplicating generated code in kotlin bindings.

  Affected platforms: Android

  Hand-written wrappers have largely been removed. The following items have been renamed:

  • Ciphersuites.DEFAULT -> CIPHERSUITES_DEFAULT
  • Ciphersuite.DEFAULT -> CIPHERSUITE_DEFAULT
  • CredentialType.Basic -> CredentialType.BASIC
  • MLSGroupId -> ConversationId
  • MLSKeyPackage -> KeyPackage
  • DeviceStatus.Valid -> DeviceStatus.VALID
  • DeviceStatus.Expired -> DeviceStatus.EXPIRED
  • DeviceStatus.Revoked -> DeviceStatus.REVOKED
  • E2eiConversationState.Verified -> E2eiConversationState.VERIFIED
  • E2eiConversationState.NotVerified -> E2eiConversationState.NOT_VERIFIED
  • E2eiConversationState.NotEnabled -> E2eiConversationState.NOT_ENABLED

• Changed exposed error type structures

  Affected platforms: iOS

  Migration

  • When pattern-matching the affected error types, add argument labels
  • When accessing inner error values, add field names

Features

• In our Swift bindings we are now protecting against concurrent access from multiple core crypto instances.
• In the decode tool we add support for listing members or identities present in a group info.

CoreCrypto 8

v8.0.3 - 2025-08-12

This is only relevant for Kotlin.

Fixes page size alignment for all supported linkers.

Adds ClientId.copyBytes().

Adds ClientId.toString().

Changes ClientId.value from ByteArray to the generated FFI type com.wire.crypto.uniffi.ClientId

v8.0.2 - 2025-07-23

This is only relevant for Kotlin.

Adds MLSKeyPackage.copyBytes().

v8.0.1 - 2025-07-23

This release is relevant only for Kotlin. It adds several pseudo-constructors and accessors for newtypes around byte vectors.

For other platforms, no relevant changes are included.

v8.0.0 - 2025-07-17

This release contains the complete API necessary for history sharing in conversations. We’ve improved the generated types in bindings to be more typesafe, and we’ve added the feature to rotate the key used for the core crypto database.

Breaking changes

• Removed canClose(), and isLocked().

  Affected platforms: Web

  Migration: Only needed if you were relying on the output of canClose() before calling close():

  Call close() directly. Instead of handling the false case of canClose(), catch the error that close() may throw: Cannot close as multiple strong refs exist, then try again.

  The behavior of close() was adjusted, so that it waits for any running transaction to finish, instead of throwing an error.

• Removed mlsInitWithClientId, mlsGenerateKeypairs, e2eiDumpPKIEnv, deleteKeypackages, getCredentialInUse

  Affected platforms: Web, Android, iOS

  Migration: not needed, no client is using these functions.

• Changed the location of the Wasm bytecode file

  Affected platforms: Web

  The Wasm bytecode file, core-crypto-ffi_bg.wasm, has been moved to a subdirectory named autogenerated. While this is an internal change and should normally not be breaking, in reality it may break the Web client, which assumes the location of that internal file.

  Migration: update relevant paths in the Web client to point to the new location, under autogenerated, including in any calls to initWasmModule.

• Added a parameter refreshToken to newOidcChallengeRequest

  Affected platforms: Web

  This fixes an inconsistency between Web and other platforms.

  Migration: pass the refresh token received from the identity provider when calling newOidcChallengeRequest.

• Added a parameter context to newOidcChallengeResponse

  Affected platforms: Web

  Migration: pass the transaction context when calling newOidcChallengeResponse.

• Added encryptedMessage field to CommitBundle

  Affected platforms: Web, Android, iOS

  This field is used to bundle encrypted history secrets with a commit that adds a new history client.

  Migration: update any pattern-matching or other code that depends on the structure of MlsCommitBundle to include the new field. Also, make sure to update your implementation of the MlsTransport protocol/interface to include this field in the payload sent to the Delivery Service.

• ClientId is a newtype, not a bare byte array.

  Affected platforms: Web, Swift

  Migration: call new ClientId(id) to construct a ClientId, and id.copyBytes() to get a byte array out.

• ClientId wrapper accepts a byte array, not a string.

  Affected platforms: Android

  Migration: call .toByteArray() on the input.

• Ciphersuite is an exported public enum, not an integer

  Affected platforms: all

  Migration: use the relevant enum variant instead of an integer.

• SecretKey, ExternalSenderKey, GroupInfo, ConversationId, KeyPackage, Welcome are now newtypes

  Affected items:

  • CoreCryptoContext.exportSecretKey (aka CoreCryptoContext.deriveAvsSecret) now returns a SecretKey
  • (kotlin) AvsSecret newtype removed in favor of SecretKey
  • CoreCryptoContext.getExternalSender now returns an ExternalSenderKey
  • ConversationConfiguration::external_senders now accepts ExternalSenderKeys
  • CoreCryptoContext.joinByExternalCommit now accepts a GroupInfo
  • GroupInfoBundle now contains a GroupInfo
  • Many CoreCryptoContext methods now accept a ConversationId newtype instead of a byte array
  • HistoryObserver and EpochObserver now produce ConversationId instances instead of byte arrays
  • CoreCryptoContext.clientKeypackages now produces KeyPackages
  • CoreCryptoContext.addClientsToConversation now accepts KeyPackages
  • CommitBundle now might contain a Welcome
  • CoreCryptoContext.processWelcomeMessage now accepts a Welcome

  Affected platforms: all

  Migration: call .copyBytes() on the newtype to get access to the raw byte vector. To construct the newtype from a byte array, just use the appropriate constructor.

  In the past, Android (but only Android) had newtypes in these instances; other clients needed to work with a raw byte vector. We’ve decided to expand the use of newtypes around byte vectors in the FFI interface. This has several benefits:

  • Increased consistency between client FFI libraries
  • Reduced thickness of the high-level FFI wrappers
  • In some cases, we can avoid bidirectional data transfers across the FFI boundary, and just move pointers around instead.

• Removed PlaintextMessage, MlsMessage and SignaturePublicKey newtypes in favor of ByteArray

  Affected platforms: Android

  The Message newtypes were only used in CoreCryptoContext.encryptMessage and CoreCryptoContext.decryptMessage. SignaturePublicKey was used only for the return value of fun getPublicKey. The only usage we found was an immediate access of the byte vector.

  These types appear to provide no type safety benefits, instead only adding a bit of friction.

Features

• Support Android environments with 16k page size
• Added a module-level function updateDatabaseKey, to update the key of an existing CoreCrypto database
• Support for history sharing which can be enabled by calling enableHistorySharing() and disabled again by calling disableHistorySharing().

CoreCrypto 7

v7.0.2 - 2025-07-07

Upgrade OpenMLS to fix a bug where the ratchet tree would sometimes become corrupt leading to broken MLS groups.

Bug Fixes

• update openmls [WPB-18569] (7ca7ba7)

v7.0.1 - 2025-06-02

Bug Fixes

• initWasm was being called with the wrong property field. (ca1706d)
• allow registering epoch observer before calling mls_init (3f0605a)

v7.0.0 - 2025-05-21

Breaking changes

The typescript bindings no longer implicitly load the wasm module when importing the core crypto module. To replace this behaviour the async initWasmModule() function has been added, which must be called before any other core crypto function.

Features

• remove top level await and expose async init method instead (ce6e566)
• expose historyClient constructor to swift (22d98de)
• expose historyClient constructor to kotlin (b16839d)
• expose historyClient constructor to wasm (3c2531a)
• expose history_client constructor publicly (c24fcc3)
• restore history secrets (5643e87)
• add fn history_client(HistorySecret) -> CoreCrypto (8b7b7d4)
• add fn generate_history_secret (a998dec)

Bug Fixes

• crypto-ffi: fix naming and attributes of WelcomeBundle fields on Wasm (1b2e88b)
• prevent cancellations during transactions (Kotlin) (75217d5)
• prevent cancellations during transactions (Kotlin) (ae621b7)

CoreCrypto 6

v6.0.1 - 2025-05-07

Bug Fixes

• swift publishing CI action (d1030e1)

v6.0.0 - 2025-05-07

• Changed the core crypto database key format, to enable validation of the same and ensure consistency between platforms
• Added a function for each platform to migrate from the old to the new key type
• Several more bug fixes, including prevention of the pending commit error

Breaking changes

• Changed the core crypto database key format

  Affected platforms: Web, Android, iOS

  Migration: before instantiating this version of core crypto for the first time, call migrateDatabaseKeyTypeToBytes() with the appropiate arguments (old key and your new key) exactly once. Then, instantiate core crypto with the new key.

  Note: Make sure the new key is not based on a string, and provide full 256 bits of entropy.

  Note: Instantiating this version of core crypto will fail before you call the migration function.

v5.4.0 - 2025-05-14

Kotlin bindings only: transactions are now NonCancellable, as required by Uniffi. This prevents a category of bug where Kotlin thinks a transaction has been cancelled, while Rust thinks it is still running.

v5.3.0- 2025-04-29

Bug Fixes

• re-throw inner error which cancelled the transaction (Swift) (0c282b2)

v5.2.0 - 2025-04-15

Bug Fixes

• add registerEpochObserver to CoreCryptoProtocol (eadf388)
• create an interface for ConversationConfiguration (b1e82bf)
• swift publishing failing due to not running on latest macos runner (dcc1890)

v5.1.0 - 2025-04-03

Bug Fixes

• broken swift bindings by publishing uniffi framework separately (2b950cc)
• don’t refer to the internal uniffi EpochObserver type in the public API (7833300)
• re-expose proteus_reload_session which removed by mistake (36f2b87)

v5.0.0 - 2025-03-21

New Swift bindings which are more ergonomic and allows for better testing by exposing the transaction context as a protocol.

New API for observing epoch changes through a callback API: registerEpochObserver. After adopting this API clients can remove their own epoch observers.

Breaking changes

• New Swift bindings are replacing the old Swift bindings.

CoreCrypto 4

v4.2.3 - 2025-03-14

• fix android publishing to maven central

v4.2.2 - 2025-03-14

• fix publishing to maven central

v4.2.1 - 2025-03-14

• expose proteusCryptoboxMigrate() [WPB-16549] (682b9fe)

v4.2.0 - 2025-02-28

• The Android release once again bundles API docs.
• The Kotlin bindings have received several API fixes in particular:
  • AcmeChallenge was missing the target property.
  • proteusGetPrekeyFingerprint was missing.
• The Typescript bindings now correctly expose WireIdentity and X509Identity.
• The code base has migrated to Rust 2024 edition.

v4.1.0 - 2025-02-07

• Add the capability to handle the case where a proposal-referencing commit arrives before the proposals it references.

(Semi-) Breaking changes

• For the case mentioned above, the corresponding error type BufferedCommit has been added.
  • Depending on the error model, this can be a breaking change.

v4.0.1 - 2025-02-05

• support entity derive for tables with hex ids (0bd3676)

v4.0.0 - 2025-01-28

• All errors crossing the FFI boundary are now logged.
• An iOS client has been added to internal interop tests, which means we now test the entire FFI stack on iOS.
• A new interface for MLS transport has been added, allowing for a much simpler and more robust CoreCrypto API.
• Removal of a number of deprecated and unnecessary functions and types.
• Completely reworked internal error handling, to allow for more precise errors.
• A number of improvements to Kotlin and Javascript bindings, making the bindings more consistent.
• The decode tool gained support for decoding MLS messages.

Breaking changes

• Deprecated functions on the CoreCrypto type that were automatically creating transactions have been removed.

  Affected platforms: Web, Android, iOS

  Migration: replace calls to functions on CoreCrypto with calls to corresponding functions on CoreCryptoContext, which is created when you explicitly create a transaction. Transactions have to be explicitly created now.

• The low-level uniffi-generated Kotlin bindings code is no longer publicly available. It should never have been used in application code directly.

  Affected platforms: Android

  Migration: make sure to use the Kotlin high-level API only.

• The Wasm bytecode generated by wasm-bindgen is now imported directly when importing the corecrypto module. This makes sure that the Wasm module is immediately initialised, without any additional steps. There is no need for the client app to know or handle the path to Wasm bytecode file.

  Additionally, it is now possible to use the same CoreCrypto module in both browser and non-browser contexts.

  Affected platforms: Web

  Migration: drop any references to core-crypto-ffi_bg.wasm and do not set the wasmFilePath argument to the CoreCrypto.init function – it is no longer used. Additionally, make sure there is no special handling or separate hosting of the Wasm bytecode file. CoreCrypto release artifacts should be used without any changes.

• Validation callbacks, as well as related error variants, have been removed.

  Affected platforms: Web, Android, iOS

  Migration: remove all implementations of authorize, userAuthorize and clientIsExistingGroupUser, as well as calls to CoreCrypto.setCallbacks.

• The MlsTransport interface has been added. This is another milestone in the effort to simplify the public API and make it more robust.

  All client applications have to provide an implementation of the new interface, which comprises only two functions, sendMessage and sendCommitBundle.

  Affected platforms: Web, Android, iOS

  Migration: implement the MlsTransport interface and call CoreCrypto.provideTransport to make CoreCrypto use your implementation.

• Functions CoreCrypto.wipe and CoreCrypto.unload have been removed. They were not providing any value.

  Affected platforms: Web, Android, iOS

  Migration: drop calls to wipe and unload. Client applications wishing to make their keys and conversations inaccessible should remove the CoreCrypto database explicitly.

• The function CoreCrypto.proteusLastErrorCode has been removed. We now have Proteus error codes attached to errors that are emitted by CoreCrypto.

  Affected platforms: Web, Android, iOS

  Migration: drop calls to proteusLastErrorCode and instead check the returned error object.

• The functions CoreCrypto.buildMetadata and CoreCrypto.version have been moved to the module level. It is no longer required to create a CoreCrypto instance to call them.

  Affected platforms: Web

  Migration: use module-level buildMetadata and version functions.

• Several changes have been made to the E2EI API.

  The function CoreCrypto.e2eiRotateAll has been removed. Client applications should instead go over each conversation individually and call CoreCrypto.e2eiRotate.

  Two new functions have been added, CoreCrypto.saveX509Credential and CoreCrypto.deleteStaleKeyPackages. The former should be used after getting a new X509 credential, while the latter should be called after generating keypackages for the new credential and replacing the stale ones in the backend.

  Affected platforms: Web, Android, iOS

  Migration: replace calls to e2eiRotateAll with iterations over conversations, calling e2eiRotate on every conversation and checking for errors. Use saveX509Credential and deleteStaleKeyPackages as appropriate (more details in API documentation).

• The proposal API has been removed, simplifying the public API a great deal. This includes functions like newProposal, newExternalProposal, clearPendingProposal, joinConversation etc.

  Affected platforms: Web, Android, iOS

  Migration: drop all calls to removed functions as they are no longer necessary with the new MLS transport interface.

CoreCrypto 3

v3.1.1 - 2025-04-15

• This release bumps the version of rusty-jwt-tools to 0.13.0, which includes additional end-to-end identity tests and test markers relevant to Bund.

v3.1.0 - 2025-02-12

• Add a test case mimicking a real life bug ([WPB-15810]), demonstrating that in some cases it was possible to generate errors by swapping the ordering of two messages.

• Add a new layer of buffering to handle that situation.

  Note

  Decrypting a message can now potentially return a MlsError::Other variant with the message

  Incoming message is a commit for which we have not yet received all the proposals. Buffering until all proposals have arrived.

  Clients do not need to take any action in response to this message. This error simply indicates that the commit has been buffered, and will be automatically unbuffered when possible.

  If the required proposal is never delivered, however, the client will eventually desync as the commit will never be processed. Clients should be on the lookout for this case and trigger their rejoin protocol in that event.

v3.0.2 - 2025-01-31

• Fix a bug which could cause certain errors to generate spurious log lines of the form

  Cannot build CoreCryptoError, falling back to standard Error! ctx: Incoming message is from an epoch too far in the future to buffer.

v3.0.1 - 2025-01-27

• Emit info log with context when buffering, restoring, or clearing buffered messages

v3.0.0 - 2024-12-11

• Fix the ‘transaction in progress’ error when there was an attempt to perform multiple transactions in parallel. This will no longer throw an error, instead the transactions will be queued and performed serially one after another.

Breaking changes

• Added the missing MLS error case OrphanWelcome.

CoreCrypto 2

v2.0.0 - 2024-12-02

• The number of public errors has been reduced and simplified. It’s no longer necessary to use the proteus_last_error_code function, since thrown error should contain all the information.
• The logger callback now includes an additional context parameter which contains additional context for a log event in the form of a JSON Object string.
• It’s now possible to change the logger and log level at runtime (see setLogLevel and setLogger).

Breaking changes

• Dropped support for i686-linux-android target.
• CoreCryptoLogger takes an additional context parameter.
• CoreCryptoError and its child errors have been refactored to reduce the amount of error we expose and provide explicit errors for Proteus errors. The errors we have removed will appear under the Other case.

  enum ProteusError {
      SessionNotFound,
      DuplicateMessage,
      RemoteIdentityChanged,
      Other(Int),
  }
  
  pub enum MlsError {
      ConversationAlreadyExists,
      DuplicateMessage,
      BufferedFutureMessage,
      WrongEpoch,
      MessageEpochTooOld,
      SelfCommitIgnored,
      UnmergedPendingGroup,
      StaleProposal,
      StaleCommit,
      Other(String)
  }