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/*
* rand.go - Reader used to generate secure random data for fscrypt.
*
* Copyright 2017 Google Inc.
* Author: Joe Richey (joerichey@google.com)
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package crypto
import (
"io"
"golang.org/x/sys/unix"
"fscrypt/util"
)
/*
RandReader uses the Linux Getrandom() syscall to read random bytes. If the
operating system has insufficient randomness, the read will fail. This is an
improvement over Go's built-in crypto/rand which will still return bytes if the
system has insufficiency entropy (https://github.com/golang/go/issues/19274).
While this syscall was only introduced in Kernel v3.17, it predates the
introduction of filesystem encryption, so it introduces no additional
compatibility issues.
*/
var RandReader io.Reader = randReader{}
// As we just call into Getrandom, no internal data is needed.
type randReader struct{}
func (r randReader) Read(buffer []byte) (int, error) {
n, err := unix.Getrandom(buffer, unix.GRND_NONBLOCK)
switch err {
case nil:
return n, nil
case unix.EAGAIN:
return 0, util.SystemErrorF("entropy pool not yet initialized")
case unix.ENOSYS:
return 0, util.SystemErrorF("getrandom not implemented; kernel must be v3.17 or later")
default:
return 0, util.SystemErrorF("cannot get randomness: %v", err)
}
}
// NewRandomKey creates a random key (from RandReader) of the specified length.
func NewRandomKey(length int) (*Key, error) {
return NewFixedLengthKeyFromReader(RandReader, length)
}
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