139 lines
3.2 KiB
Go
139 lines
3.2 KiB
Go
// Copyright 2010 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build darwin freebsd linux netbsd openbsd plan9
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// Unix cryptographically secure pseudorandom number
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// generator.
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package rand
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import (
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"bufio"
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"crypto/aes"
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"crypto/cipher"
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"io"
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"os"
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"runtime"
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"sync"
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"time"
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)
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// Easy implementation: read from /dev/urandom.
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// This is sufficient on Linux, OS X, and FreeBSD.
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func init() {
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if runtime.GOOS == "plan9" {
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Reader = newReader(nil)
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} else {
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Reader = &devReader{name: "/dev/urandom"}
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}
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}
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// A devReader satisfies reads by reading the file named name.
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type devReader struct {
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name string
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f io.Reader
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mu sync.Mutex
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}
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func (r *devReader) Read(b []byte) (n int, err error) {
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r.mu.Lock()
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defer r.mu.Unlock()
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if r.f == nil {
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f, err := os.Open(r.name)
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if f == nil {
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return 0, err
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}
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if runtime.GOOS == "plan9" {
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r.f = f
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} else {
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r.f = bufio.NewReader(f)
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}
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}
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return r.f.Read(b)
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}
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// Alternate pseudo-random implementation for use on
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// systems without a reliable /dev/urandom.
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// newReader returns a new pseudorandom generator that
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// seeds itself by reading from entropy. If entropy == nil,
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// the generator seeds itself by reading from the system's
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// random number generator, typically /dev/random.
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// The Read method on the returned reader always returns
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// the full amount asked for, or else it returns an error.
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//
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// The generator uses the X9.31 algorithm with AES-128,
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// reseeding after every 1 MB of generated data.
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func newReader(entropy io.Reader) io.Reader {
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if entropy == nil {
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entropy = &devReader{name: "/dev/random"}
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}
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return &reader{entropy: entropy}
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}
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type reader struct {
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mu sync.Mutex
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budget int // number of bytes that can be generated
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cipher cipher.Block
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entropy io.Reader
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time, seed, dst, key [aes.BlockSize]byte
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}
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func (r *reader) Read(b []byte) (n int, err error) {
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r.mu.Lock()
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defer r.mu.Unlock()
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n = len(b)
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for len(b) > 0 {
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if r.budget == 0 {
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_, err := io.ReadFull(r.entropy, r.seed[0:])
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if err != nil {
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return n - len(b), err
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}
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_, err = io.ReadFull(r.entropy, r.key[0:])
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if err != nil {
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return n - len(b), err
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}
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r.cipher, err = aes.NewCipher(r.key[0:])
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if err != nil {
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return n - len(b), err
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}
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r.budget = 1 << 20 // reseed after generating 1MB
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}
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r.budget -= aes.BlockSize
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// ANSI X9.31 (== X9.17) algorithm, but using AES in place of 3DES.
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//
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// single block:
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// t = encrypt(time)
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// dst = encrypt(t^seed)
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// seed = encrypt(t^dst)
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ns := time.Now().UnixNano()
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r.time[0] = byte(ns >> 56)
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r.time[1] = byte(ns >> 48)
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r.time[2] = byte(ns >> 40)
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r.time[3] = byte(ns >> 32)
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r.time[4] = byte(ns >> 24)
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r.time[5] = byte(ns >> 16)
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r.time[6] = byte(ns >> 8)
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r.time[7] = byte(ns)
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r.cipher.Encrypt(r.time[0:], r.time[0:])
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for i := 0; i < aes.BlockSize; i++ {
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r.dst[i] = r.time[i] ^ r.seed[i]
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}
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r.cipher.Encrypt(r.dst[0:], r.dst[0:])
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for i := 0; i < aes.BlockSize; i++ {
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r.seed[i] = r.time[i] ^ r.dst[i]
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}
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r.cipher.Encrypt(r.seed[0:], r.seed[0:])
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m := copy(b, r.dst[0:])
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b = b[m:]
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}
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return n, nil
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}
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