mautrix-go/crypto/cross_sign_ssss.go

// Copyright (c) 2020 Nikos Filippakis
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

package crypto

import (
	"context"
	"fmt"

	"maunium.net/go/mautrix"
	"maunium.net/go/mautrix/crypto/ssss"
	"maunium.net/go/mautrix/crypto/utils"
	"maunium.net/go/mautrix/event"
	"maunium.net/go/mautrix/id"
)

// FetchCrossSigningKeysFromSSSS fetches all the cross-signing keys from SSSS, decrypts them using the given key and stores them in the olm machine.
func (mach *OlmMachine) FetchCrossSigningKeysFromSSSS(ctx context.Context, key *ssss.Key) error {
	masterKey, err := mach.retrieveDecryptXSigningKey(ctx, event.AccountDataCrossSigningMaster, key)
	if err != nil {
		return err
	}
	selfSignKey, err := mach.retrieveDecryptXSigningKey(ctx, event.AccountDataCrossSigningSelf, key)
	if err != nil {
		return err
	}
	userSignKey, err := mach.retrieveDecryptXSigningKey(ctx, event.AccountDataCrossSigningUser, key)
	if err != nil {
		return err
	}

	return mach.ImportCrossSigningKeys(CrossSigningSeeds{
		MasterKey:      masterKey[:],
		SelfSigningKey: selfSignKey[:],
		UserSigningKey: userSignKey[:],
	})
}

// retrieveDecryptXSigningKey retrieves the requested cross-signing key from SSSS and decrypts it using the given SSSS key.
func (mach *OlmMachine) retrieveDecryptXSigningKey(ctx context.Context, keyName event.Type, key *ssss.Key) ([utils.AESCTRKeyLength]byte, error) {
	var decryptedKey [utils.AESCTRKeyLength]byte
	var encData ssss.EncryptedAccountDataEventContent

	// retrieve and parse the account data for this key type from SSSS
	err := mach.Client.GetAccountData(ctx, keyName.Type, &encData)
	if err != nil {
		return decryptedKey, err
	}

	decrypted, err := encData.Decrypt(keyName.Type, key)
	if err != nil {
		return decryptedKey, err
	}
	copy(decryptedKey[:], decrypted)
	return decryptedKey, nil
}

func (mach *OlmMachine) GenerateAndUploadCrossSigningKeysWithPassword(ctx context.Context, userPassword, passphrase string) (string, *CrossSigningKeysCache, error) {
	return mach.GenerateAndUploadCrossSigningKeys(ctx, func(uiResp *mautrix.RespUserInteractive) interface{} {
		return &mautrix.ReqUIAuthLogin{
			BaseAuthData: mautrix.BaseAuthData{
				Type:    mautrix.AuthTypePassword,
				Session: uiResp.Session,
			},
			User:     mach.Client.UserID.String(),
			Password: userPassword,
		}
	}, passphrase)
}

// GenerateAndUploadCrossSigningKeys generates a new key with all corresponding cross-signing keys.
//
// A passphrase can be provided to generate the SSSS key. If the passphrase is empty, a random key
// is used. The base58-formatted recovery key is the first return parameter.
//
// The account password of the user is required for uploading keys to the server.
func (mach *OlmMachine) GenerateAndUploadCrossSigningKeys(ctx context.Context, uiaCallback mautrix.UIACallback, passphrase string) (string, *CrossSigningKeysCache, error) {
	key, err := mach.SSSS.GenerateAndUploadKey(ctx, passphrase)
	if err != nil {
		return "", nil, fmt.Errorf("failed to generate and upload SSSS key: %w", err)
	}

	// generate the three cross-signing keys
	keysCache, err := mach.GenerateCrossSigningKeys()
	if err != nil {
		return "", nil, err
	}

	// Store the private keys in SSSS
	if err := mach.UploadCrossSigningKeysToSSSS(ctx, key, keysCache); err != nil {
		return "", nil, fmt.Errorf("failed to upload cross-signing keys to SSSS: %w", err)
	}

	// Publish cross-signing keys
	err = mach.PublishCrossSigningKeys(ctx, keysCache, uiaCallback)
	if err != nil {
		return "", nil, fmt.Errorf("failed to publish cross-signing keys: %w", err)
	}

	err = mach.SSSS.SetDefaultKeyID(ctx, key.ID)
	if err != nil {
		return "", nil, fmt.Errorf("failed to mark %s as the default key: %w", key.ID, err)
	}

	return key.RecoveryKey(), keysCache, nil
}

// UploadCrossSigningKeysToSSSS stores the given cross-signing keys on the server encrypted with the given key.
func (mach *OlmMachine) UploadCrossSigningKeysToSSSS(ctx context.Context, key *ssss.Key, keys *CrossSigningKeysCache) error {
	if err := mach.SSSS.SetEncryptedAccountData(ctx, event.AccountDataCrossSigningMaster, keys.MasterKey.Seed(), key); err != nil {
		return err
	}
	if err := mach.SSSS.SetEncryptedAccountData(ctx, event.AccountDataCrossSigningSelf, keys.SelfSigningKey.Seed(), key); err != nil {
		return err
	}
	if err := mach.SSSS.SetEncryptedAccountData(ctx, event.AccountDataCrossSigningUser, keys.UserSigningKey.Seed(), key); err != nil {
		return err
	}

	// Also store these locally
	if err := mach.CryptoStore.PutCrossSigningKey(ctx, mach.Client.UserID, id.XSUsageMaster, keys.MasterKey.PublicKey()); err != nil {
		return err
	}
	if err := mach.CryptoStore.PutCrossSigningKey(ctx, mach.Client.UserID, id.XSUsageSelfSigning, keys.SelfSigningKey.PublicKey()); err != nil {
		return err
	}
	if err := mach.CryptoStore.PutCrossSigningKey(ctx, mach.Client.UserID, id.XSUsageUserSigning, keys.UserSigningKey.PublicKey()); err != nil {
		return err
	}

	return nil
}