103 lines
3.1 KiB
Go
103 lines
3.1 KiB
Go
// Copyright (c) 2020 Tulir Asokan
|
|
//
|
|
// 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 ssss
|
|
|
|
import (
|
|
"encoding/base64"
|
|
"fmt"
|
|
"strings"
|
|
|
|
"maunium.net/go/mautrix/crypto/utils"
|
|
)
|
|
|
|
// KeyMetadata represents server-side metadata about a SSSS key. The metadata can be used to get
|
|
// the actual SSSS key from a passphrase or recovery key.
|
|
type KeyMetadata struct {
|
|
id string
|
|
|
|
Algorithm Algorithm `json:"algorithm"`
|
|
IV string `json:"iv"`
|
|
MAC string `json:"mac"`
|
|
Passphrase *PassphraseMetadata `json:"passphrase,omitempty"`
|
|
}
|
|
|
|
// VerifyRecoveryKey verifies that the given passphrase is valid and returns the computed SSSS key.
|
|
func (kd *KeyMetadata) VerifyPassphrase(passphrase string) (*Key, error) {
|
|
ssssKey, err := kd.Passphrase.GetKey(passphrase)
|
|
if err != nil {
|
|
return nil, err
|
|
} else if !kd.VerifyKey(ssssKey) {
|
|
return nil, ErrIncorrectSSSSKey
|
|
}
|
|
|
|
return &Key{
|
|
ID: kd.id,
|
|
Key: ssssKey,
|
|
Metadata: kd,
|
|
}, nil
|
|
}
|
|
|
|
// VerifyRecoveryKey verifies that the given recovery key is valid and returns the decoded SSSS key.
|
|
func (kd *KeyMetadata) VerifyRecoveryKey(recoverKey string) (*Key, error) {
|
|
ssssKey := utils.DecodeBase58RecoveryKey(recoverKey)
|
|
if ssssKey == nil {
|
|
return nil, ErrInvalidRecoveryKey
|
|
} else if !kd.VerifyKey(ssssKey) {
|
|
return nil, ErrIncorrectSSSSKey
|
|
}
|
|
|
|
return &Key{
|
|
ID: kd.id,
|
|
Key: ssssKey,
|
|
Metadata: kd,
|
|
}, nil
|
|
}
|
|
|
|
// VerifyKey verifies the SSSS key is valid by calculating and comparing its MAC.
|
|
func (kd *KeyMetadata) VerifyKey(key []byte) bool {
|
|
return strings.ReplaceAll(kd.MAC, "=", "") == strings.ReplaceAll(kd.calculateHash(key), "=", "")
|
|
}
|
|
|
|
// calculateHash calculates the hash used for checking if the key is entered correctly as described
|
|
// in the spec: https://matrix.org/docs/spec/client_server/unstable#m-secret-storage-v1-aes-hmac-sha2
|
|
func (kd *KeyMetadata) calculateHash(key []byte) string {
|
|
aesKey, hmacKey := utils.DeriveKeysSHA256(key, "")
|
|
|
|
var ivBytes [utils.AESCTRIVLength]byte
|
|
_, _ = base64.StdEncoding.Decode(ivBytes[:], []byte(kd.IV))
|
|
|
|
cipher := utils.XorA256CTR(make([]byte, utils.AESCTRKeyLength), aesKey, ivBytes)
|
|
|
|
return utils.HMACSHA256B64(cipher, hmacKey)
|
|
}
|
|
|
|
// PassphraseMetadata represents server-side metadata about a SSSS key passphrase.
|
|
type PassphraseMetadata struct {
|
|
Algorithm PassphraseAlgorithm `json:"algorithm"`
|
|
Iterations int `json:"iterations"`
|
|
Salt string `json:"salt"`
|
|
Bits int `json:"bits"`
|
|
}
|
|
|
|
// GetKey gets the SSSS key from the passphrase.
|
|
func (pd *PassphraseMetadata) GetKey(passphrase string) ([]byte, error) {
|
|
if pd == nil {
|
|
return nil, ErrNoPassphrase
|
|
}
|
|
|
|
if pd.Algorithm != PassphraseAlgorithmPBKDF2 {
|
|
return nil, fmt.Errorf("%w: %s", ErrUnsupportedPassphraseAlgorithm, pd.Algorithm)
|
|
}
|
|
|
|
bits := 256
|
|
if pd.Bits != 0 {
|
|
bits = pd.Bits
|
|
}
|
|
|
|
return utils.PBKDF2SHA512([]byte(passphrase), []byte(pd.Salt), pd.Iterations, bits), nil
|
|
}
|