mirror of
https://github.com/restic/restic.git
synced 2024-08-23 04:40:46 +02:00
346 lines
8.9 KiB
Go
346 lines
8.9 KiB
Go
package restic
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import (
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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/restic/restic/backend"
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"github.com/restic/restic/chunker"
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"github.com/restic/restic/debug"
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"golang.org/x/crypto/poly1305"
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)
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// max size is 8MiB, defined in chunker
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const macSize = poly1305.TagSize // Poly1305 size is 16 byte
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const maxCiphertextSize = ivSize + chunker.MaxSize + macSize
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const CiphertextExtension = ivSize + macSize
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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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)
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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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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 *MasterKeys
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master *MasterKeys
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name string
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}
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// MasterKeys holds signing and encryption keys for a repository. It is stored
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// encrypted and signed as a JSON data structure in the Data field of the Key
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// structure. For the master key, the secret random polynomial used for content
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// defined chunking is included.
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type MasterKeys struct {
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Sign MACKey `json:"sign"`
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Encrypt AESKey `json:"encrypt"`
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ChunkerPolynomial chunker.Pol `json:"chunker_polynomial,omitempty"`
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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(s Server, password string) (*Key, error) {
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return AddKey(s, password, nil)
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}
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// OpenKey tries do decrypt the key specified by name with the given password.
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func OpenKey(s Server, name string, password string) (*Key, error) {
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k, err := LoadKey(s, name)
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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 = kdf(k, 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([]byte{}, 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 = &MasterKeys{}
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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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k.name = name
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// test if polynomial is valid and irreducible
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if k.master.ChunkerPolynomial == 0 {
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return nil, errors.New("Polynomial for content defined chunking is zero")
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}
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if !k.master.ChunkerPolynomial.Irreducible() {
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return nil, errors.New("Polynomial for content defined chunking is invalid")
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}
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debug.Log("OpenKey", "Master keys loaded, polynomial %v", k.master.ChunkerPolynomial)
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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(s Server, password string) (*Key, error) {
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// try all keys in repo
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done := make(chan struct{})
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defer close(done)
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for name := range s.List(backend.Key, done) {
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key, err := OpenKey(s, name, 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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// LoadKey loads a key from the backend.
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func LoadKey(s Server, name string) (*Key, error) {
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// extract data from repo
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rd, err := s.be.Get(backend.Key, name)
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if err != nil {
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return nil, err
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}
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defer rd.Close()
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// restore json
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dec := json.NewDecoder(rd)
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k := Key{}
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err = dec.Decode(&k)
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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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// AddKey adds a new key to an already existing repository.
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func AddKey(s Server, password string, template *Key) (*Key, 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 KDF to derive user key
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newkey.user, err = kdf(newkey, password)
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if err != nil {
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return nil, err
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}
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if template == nil {
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// generate new random master keys
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newkey.master = generateRandomKeys()
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// generate random polynomial for cdc
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p, err := chunker.RandomPolynomial()
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if err != nil {
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debug.Log("AddKey", "error generating new polynomial for cdc: %v", err)
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return nil, err
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}
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debug.Log("AddKey", "generated new polynomial for cdc: %v", p)
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newkey.master.ChunkerPolynomial = p
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} else {
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// copy master keys from old key
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newkey.master = template.master
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}
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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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blob, err := s.be.Create()
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if err != nil {
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return nil, err
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}
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plainhw := backend.NewHashingWriter(blob, sha256.New())
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_, err = plainhw.Write(buf)
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if err != nil {
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return nil, err
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}
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name := backend.ID(plainhw.Sum(nil)).String()
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err = blob.Finalize(backend.Key, name)
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if err != nil {
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return nil, err
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}
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newkey.name = name
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FreeChunkBuf("key", newkey.Data)
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return newkey, 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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// EncryptUser encrypts and signs data with the user key. Stored in ciphertext
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// is IV || Ciphertext || MAC.
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func (k *Key) EncryptUser(ciphertext, plaintext []byte) (int, error) {
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return 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 || MAC. Returns the ciphertext length.
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func (k *Key) Encrypt(ciphertext, plaintext []byte) (int, error) {
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return Encrypt(k.master, ciphertext, plaintext)
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}
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// EncryptTo encrypts and signs data with the master key. The returned
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// io.Writer writes IV || Ciphertext || HMAC. For the hash function, SHA256 is
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// used.
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func (k *Key) EncryptTo(wr io.Writer) io.WriteCloser {
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return EncryptTo(k.master, wr)
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}
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// EncryptUserTo encrypts and signs data with the user key. The returned
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// io.Writer writes IV || Ciphertext || HMAC. For the hash function, SHA256 is
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// used.
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func (k *Key) EncryptUserTo(wr io.Writer) io.WriteCloser {
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return EncryptTo(k.user, wr)
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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 || MAC.
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func (k *Key) Decrypt(plaintext, ciphertext []byte) ([]byte, error) {
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return Decrypt(k.master, plaintext, ciphertext)
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}
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// DecryptUser verifes and decrypts the ciphertext with the user key. Ciphertext
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// must be in the form IV || Ciphertext || MAC.
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func (k *Key) DecryptUser(plaintext, ciphertext []byte) ([]byte, error) {
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return Decrypt(k.user, plaintext, ciphertext)
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}
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// DecryptFrom verifies and decrypts the ciphertext read from rd and makes it
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// available on the returned Reader. Ciphertext must be in the form IV ||
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// Ciphertext || MAC. In order to correctly verify the ciphertext, rd is
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// drained, locally buffered and made available on the returned Reader
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// afterwards. If an MAC verification failure is observed, it is returned
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// immediately.
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func (k *Key) DecryptFrom(rd io.Reader) (io.ReadCloser, error) {
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return DecryptFrom(k.master, rd)
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}
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// DecryptFrom verifies and decrypts the ciphertext read from rd with the user
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// key and makes it available on the returned Reader. Ciphertext must be in the
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// form IV || Ciphertext || MAC. In order to correctly verify the ciphertext,
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// rd is drained, locally buffered and made available on the returned Reader
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// afterwards. If an MAC verification failure is observed, it is returned
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// immediately.
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func (k *Key) DecryptUserFrom(rd io.Reader) (io.ReadCloser, error) {
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return DecryptFrom(k.user, rd)
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}
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// Master() returns the master keys for this repository. Only included for
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// debug purposes.
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func (k *Key) Master() *MasterKeys {
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return k.master
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}
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// User() returns the user keys for this key. Only included for debug purposes.
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func (k *Key) User() *MasterKeys {
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return k.user
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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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func (k Key) Name() string {
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return k.name
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}
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