Add streaming encrypt functions

key.go

@@ -1,6 +1,7 @@
 package restic
 
 import (
+	"bytes"
 	"crypto/aes"
 	"crypto/cipher"
 	"crypto/hmac"
@@ -9,6 +10,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"hash"
 	"io"
 	"os"
 	"os/user"
@@ -315,6 +317,95 @@ func (k *Key) Encrypt(ciphertext, plaintext []byte) (int, error) {
 	return k.encrypt(k.master, ciphertext, plaintext)
 }
 
+type HashReader struct {
+	r      io.Reader
+	h      hash.Hash
+	sum    []byte
+	closed bool
+}
+
+func NewHashReader(r io.Reader, h hash.Hash) *HashReader {
+	return &HashReader{
+		h:   h,
+		r:   io.TeeReader(r, h),
+		sum: make([]byte, 0, h.Size()),
+	}
+}
+
+func (h *HashReader) Read(p []byte) (n int, err error) {
+	if !h.closed {
+		n, err = h.r.Read(p)
+
+		if err == io.EOF {
+			h.closed = true
+			h.sum = h.h.Sum(h.sum)
+		} else if err != nil {
+			return
+		}
+	}
+
+	if h.closed {
+		// output hash
+		r := len(p) - n
+
+		if r > 0 {
+			c := copy(p[n:], h.sum)
+			h.sum = h.sum[c:]
+
+			n += c
+			err = nil
+		}
+
+		if len(h.sum) == 0 {
+			err = io.EOF
+		}
+	}
+
+	return
+}
+
+// encryptFrom encrypts and signs data read from rd with ks. The returned
+// io.Reader reads IV || Ciphertext || HMAC. For the hash function, SHA256 is
+// used.
+func (k *Key) encryptFrom(ks *keys, rd io.Reader) io.Reader {
+	// create IV
+	iv := make([]byte, ivSize)
+
+	_, err := io.ReadFull(rand.Reader, iv)
+	if err != nil {
+		panic(fmt.Sprintf("unable to generate new random iv: %v", err))
+	}
+
+	c, err := aes.NewCipher(ks.Encrypt)
+	if err != nil {
+		panic(fmt.Sprintf("unable to create cipher: %v", err))
+	}
+
+	ivReader := bytes.NewReader(iv)
+
+	encryptReader := cipher.StreamReader{
+		R: rd,
+		S: cipher.NewCTR(c, iv),
+	}
+
+	return NewHashReader(io.MultiReader(ivReader, encryptReader),
+		hmac.New(sha256.New, ks.Sign))
+}
+
+// EncryptFrom encrypts and signs data read from rd with the master key. The
+// returned io.Reader reads IV || Ciphertext || HMAC. For the hash function,
+// SHA256 is used.
+func (k *Key) EncryptFrom(rd io.Reader) io.Reader {
+	return k.encryptFrom(k.master, rd)
+}
+
+// EncryptFrom encrypts and signs data read from rd with the user key. The
+// returned io.Reader reads IV || Ciphertext || HMAC. For the hash function,
+// SHA256 is used.
+func (k *Key) EncryptUserFrom(rd io.Reader) io.Reader {
+	return k.encryptFrom(k.user, rd)
+}
+
 // Decrypt verifes and decrypts the ciphertext. Ciphertext must be in the form
 // IV || Ciphertext || HMAC.
 func (k *Key) decrypt(ks *keys, ciphertext []byte) ([]byte, error) {