mirror of
https://github.com/restic/restic.git
synced 2024-09-03 01:57:29 +02:00
449 lines
10 KiB
Go
449 lines
10 KiB
Go
package khepri
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import (
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"crypto/aes"
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"crypto/cipher"
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"crypto/hmac"
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"crypto/rand"
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"crypto/sha256"
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"encoding/json"
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"errors"
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"fmt"
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"io"
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"os"
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"os/user"
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"time"
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"github.com/fd0/khepri/backend"
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"github.com/fd0/khepri/chunker"
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"golang.org/x/crypto/scrypt"
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)
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// max size is 8MiB, defined in chunker
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const ivSize = aes.BlockSize
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const hmacSize = sha256.Size
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const maxCiphertextSize = ivSize + chunker.MaxSize + hmacSize
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const CiphertextExtension = ivSize + hmacSize
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var (
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// ErrUnauthenticated is returned when ciphertext verification has failed.
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ErrUnauthenticated = errors.New("ciphertext verification failed")
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// ErrNoKeyFound is returned when no key for the repository could be decrypted.
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ErrNoKeyFound = errors.New("no key could be found")
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// ErrBufferTooSmall is returned when the destination slice is too small
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// for the ciphertext.
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ErrBufferTooSmall = errors.New("destination buffer too small")
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)
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// TODO: figure out scrypt values on the fly depending on the current
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// hardware.
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const (
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scryptN = 65536
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scryptR = 8
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scryptP = 1
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scryptSaltsize = 64
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aesKeysize = 32 // for AES256
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hmacKeysize = 32 // for HMAC with SHA256
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)
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// Key represents an encrypted master key for a repository.
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type Key struct {
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Created time.Time `json:"created"`
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Username string `json:"username"`
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Hostname string `json:"hostname"`
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Comment string `json:"comment,omitempty"`
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KDF string `json:"kdf"`
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N int `json:"N"`
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R int `json:"r"`
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P int `json:"p"`
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Salt []byte `json:"salt"`
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Data []byte `json:"data"`
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user *keys
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master *keys
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}
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// keys is a JSON structure that holds signing and encryption keys.
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type keys struct {
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Sign []byte
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Encrypt []byte
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}
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// CreateKey initializes a master key in the given backend and encrypts it with
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// the password.
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func CreateKey(be backend.Server, password string) (*Key, error) {
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// fill meta data about key
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k := &Key{
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Created: time.Now(),
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KDF: "scrypt",
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N: scryptN,
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R: scryptR,
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P: scryptP,
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}
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hn, err := os.Hostname()
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if err == nil {
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k.Hostname = hn
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}
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usr, err := user.Current()
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if err == nil {
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k.Username = usr.Username
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}
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// generate random salt
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k.Salt = make([]byte, scryptSaltsize)
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n, err := rand.Read(k.Salt)
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if n != scryptSaltsize || err != nil {
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panic("unable to read enough random bytes for salt")
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}
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// call scrypt() to derive user key
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k.user, err = k.scrypt(password)
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if err != nil {
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return nil, err
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}
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// generate new random master keys
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k.master, err = k.newKeys()
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if err != nil {
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return nil, err
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}
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// encrypt master keys (as json) with user key
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buf, err := json.Marshal(k.master)
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if err != nil {
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return nil, err
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}
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k.Data = GetChunkBuf("key")
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n, err = k.EncryptUser(k.Data, buf)
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k.Data = k.Data[:n]
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// dump as json
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buf, err = json.Marshal(k)
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if err != nil {
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return nil, err
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}
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// store in repository and return
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_, err = be.Create(backend.Key, buf)
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if err != nil {
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return nil, err
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}
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FreeChunkBuf("key", k.Data)
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return k, nil
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}
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// OpenKey tries do decrypt the key specified by id with the given password.
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func OpenKey(be backend.Server, id backend.ID, password string) (*Key, error) {
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// extract data from repo
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data, err := be.Get(backend.Key, id)
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if err != nil {
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return nil, err
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}
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// restore json
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k := &Key{}
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err = json.Unmarshal(data, k)
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if err != nil {
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return nil, err
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}
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// check KDF
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if k.KDF != "scrypt" {
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return nil, errors.New("only supported KDF is scrypt()")
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}
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// derive user key
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k.user, err = k.scrypt(password)
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if err != nil {
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return nil, err
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}
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// decrypt master keys
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buf, err := k.DecryptUser(k.Data)
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if err != nil {
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return nil, err
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}
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// restore json
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k.master = &keys{}
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err = json.Unmarshal(buf, k.master)
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if err != nil {
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return nil, err
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}
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return k, nil
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}
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// SearchKey tries to decrypt all keys in the backend with the given password.
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// If none could be found, ErrNoKeyFound is returned.
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func SearchKey(be backend.Server, password string) (*Key, error) {
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// list all keys
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ids, err := be.List(backend.Key)
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if err != nil {
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panic(err)
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}
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// try all keys in repo
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var key *Key
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for _, id := range ids {
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key, err = OpenKey(be, id, password)
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if err != nil {
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continue
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}
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return key, nil
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}
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return nil, ErrNoKeyFound
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}
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// AddKey adds a new key to an already existing repository.
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func (oldkey *Key) AddKey(be backend.Server, password string) (backend.ID, error) {
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// fill meta data about key
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newkey := &Key{
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Created: time.Now(),
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KDF: "scrypt",
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N: scryptN,
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R: scryptR,
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P: scryptP,
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}
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hn, err := os.Hostname()
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if err == nil {
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newkey.Hostname = hn
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}
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usr, err := user.Current()
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if err == nil {
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newkey.Username = usr.Username
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}
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// generate random salt
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newkey.Salt = make([]byte, scryptSaltsize)
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n, err := rand.Read(newkey.Salt)
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if n != scryptSaltsize || err != nil {
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panic("unable to read enough random bytes for salt")
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}
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// call scrypt() to derive user key
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newkey.user, err = newkey.scrypt(password)
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if err != nil {
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return nil, err
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}
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// copy master keys from oldkey
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newkey.master = oldkey.master
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// encrypt master keys (as json) with user key
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buf, err := json.Marshal(newkey.master)
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if err != nil {
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return nil, err
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}
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newkey.Data = GetChunkBuf("key")
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n, err = newkey.EncryptUser(newkey.Data, buf)
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newkey.Data = newkey.Data[:n]
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// dump as json
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buf, err = json.Marshal(newkey)
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if err != nil {
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return nil, err
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}
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// store in repository and return
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id, err := be.Create(backend.Key, buf)
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if err != nil {
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return nil, err
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}
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FreeChunkBuf("key", newkey.Data)
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return id, nil
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}
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func (k *Key) scrypt(password string) (*keys, error) {
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if len(k.Salt) == 0 {
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return nil, fmt.Errorf("scrypt() called with empty salt")
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}
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keybytes := hmacKeysize + aesKeysize
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scryptKeys, err := scrypt.Key([]byte(password), k.Salt, k.N, k.R, k.P, keybytes)
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if err != nil {
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return nil, fmt.Errorf("error deriving keys from password: %v", err)
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}
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if len(scryptKeys) != keybytes {
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return nil, fmt.Errorf("invalid numbers of bytes expanded from scrypt(): %d", len(scryptKeys))
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}
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ks := &keys{
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Encrypt: scryptKeys[:aesKeysize],
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Sign: scryptKeys[aesKeysize:],
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}
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return ks, nil
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}
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func (k *Key) newKeys() (*keys, error) {
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ks := &keys{
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Encrypt: make([]byte, aesKeysize),
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Sign: make([]byte, hmacKeysize),
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}
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n, err := rand.Read(ks.Encrypt)
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if n != aesKeysize || err != nil {
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panic("unable to read enough random bytes for encryption key")
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}
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n, err = rand.Read(ks.Sign)
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if n != hmacKeysize || err != nil {
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panic("unable to read enough random bytes for signing key")
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}
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return ks, nil
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}
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func (k *Key) newIV(buf []byte) error {
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_, err := io.ReadFull(rand.Reader, buf[:ivSize])
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buf = buf[:ivSize]
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if err != nil {
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return err
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}
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return nil
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}
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// Encrypt encrypts and signs data. Stored in ciphertext is IV || Ciphertext ||
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// HMAC. Encrypt returns the ciphertext's length. For the hash function, SHA256
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// is used, so the overhead is 16+32=48 byte.
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func (k *Key) encrypt(ks *keys, ciphertext, plaintext []byte) (int, error) {
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if cap(ciphertext) < len(plaintext)+ivSize+hmacSize {
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return 0, ErrBufferTooSmall
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}
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_, err := io.ReadFull(rand.Reader, ciphertext[:ivSize])
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if err != nil {
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panic(fmt.Sprintf("unable to generate new random iv: %v", err))
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}
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c, err := aes.NewCipher(ks.Encrypt)
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if err != nil {
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panic(fmt.Sprintf("unable to create cipher: %v", err))
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}
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e := cipher.NewCTR(c, ciphertext[:ivSize])
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e.XORKeyStream(ciphertext[ivSize:cap(ciphertext)], plaintext)
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ciphertext = ciphertext[:ivSize+len(plaintext)]
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hm := hmac.New(sha256.New, ks.Sign)
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n, err := hm.Write(ciphertext)
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if err != nil || n != len(ciphertext) {
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panic(fmt.Sprintf("unable to calculate hmac of ciphertext: %v", err))
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}
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ciphertext = hm.Sum(ciphertext)
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return len(ciphertext), nil
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}
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// EncryptUser encrypts and signs data with the user key. Stored in ciphertext
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// is IV || Ciphertext || HMAC. Returns the ciphertext length. For the hash
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// function, SHA256 is used, so the overhead is 16+32=48 byte.
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func (k *Key) EncryptUser(ciphertext, plaintext []byte) (int, error) {
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return k.encrypt(k.user, ciphertext, plaintext)
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}
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// Encrypt encrypts and signs data with the master key. Stored in ciphertext is
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// IV || Ciphertext || HMAC. Returns the ciphertext length. For the hash
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// function, SHA256 is used, so the overhead is 16+32=48 byte.
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func (k *Key) Encrypt(ciphertext, plaintext []byte) (int, error) {
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return k.encrypt(k.master, ciphertext, plaintext)
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}
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// Decrypt verifes and decrypts the ciphertext. Ciphertext must be in the form
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// IV || Ciphertext || HMAC.
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func (k *Key) decrypt(ks *keys, ciphertext []byte) ([]byte, error) {
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// check for plausible length
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if len(ciphertext) <= ivSize+hmacSize {
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panic("trying to decryipt invalid data: ciphertext too small")
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}
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hm := hmac.New(sha256.New, ks.Sign)
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// extract hmac
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l := len(ciphertext) - hm.Size()
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ciphertext, mac := ciphertext[:l], ciphertext[l:]
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// calculate new hmac
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n, err := hm.Write(ciphertext)
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if err != nil || n != len(ciphertext) {
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panic(fmt.Sprintf("unable to calculate hmac of ciphertext, err %v", err))
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}
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// verify hmac
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mac2 := hm.Sum(nil)
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if !hmac.Equal(mac, mac2) {
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return nil, ErrUnauthenticated
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}
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// extract iv
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iv, ciphertext := ciphertext[:aes.BlockSize], ciphertext[aes.BlockSize:]
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// decrypt data
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c, err := aes.NewCipher(ks.Encrypt)
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if err != nil {
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panic(fmt.Sprintf("unable to create cipher: %v", err))
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}
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// decrypt
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e := cipher.NewCTR(c, iv)
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plaintext := make([]byte, len(ciphertext))
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e.XORKeyStream(plaintext, ciphertext)
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return plaintext, nil
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}
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// Decrypt verifes and decrypts the ciphertext with the master key. Ciphertext
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// must be in the form IV || Ciphertext || HMAC.
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func (k *Key) Decrypt(ciphertext []byte) ([]byte, error) {
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return k.decrypt(k.master, ciphertext)
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}
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// DecryptUser verifes and decrypts the ciphertext with the master key. Ciphertext
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// must be in the form IV || Ciphertext || HMAC.
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func (k *Key) DecryptUser(ciphertext []byte) ([]byte, error) {
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return k.decrypt(k.user, ciphertext)
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}
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// Each calls backend.Each() with the given parameters, Decrypt() on the
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// ciphertext and, on successful decryption, f with the plaintext.
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func (k *Key) Each(be backend.Server, t backend.Type, f func(backend.ID, []byte, error)) error {
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return backend.Each(be, t, func(id backend.ID, data []byte, e error) {
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if e != nil {
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f(id, nil, e)
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return
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}
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buf, err := k.Decrypt(data)
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if err != nil {
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f(id, nil, err)
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return
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}
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f(id, buf, nil)
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})
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}
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func (k *Key) String() string {
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if k == nil {
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return "<Key nil>"
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}
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return fmt.Sprintf("<Key of %s@%s, created on %s>", k.Username, k.Hostname, k.Created)
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}
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