Subversion Repositories openrisc

// Copyright 2010 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// +build darwin freebsd linux netbsd openbsd

// Unix cryptographically secure pseudorandom number
// generator.

package rand

import (
        "bufio"
        "crypto/aes"
        "io"
        "os"
        "sync"
        "time"
)

// Easy implementation: read from /dev/urandom.
// This is sufficient on Linux, OS X, and FreeBSD.

func init() { Reader = &devReader{name: "/dev/urandom"} }

// A devReader satisfies reads by reading the file named name.
type devReader struct {
        name string
        f    io.Reader
        mu   sync.Mutex
}

func (r *devReader) Read(b []byte) (n int, err error) {
        r.mu.Lock()
        defer r.mu.Unlock()
        if r.f == nil {
                f, err := os.Open(r.name)
                if f == nil {
                        return 0, err
                }
                r.f = bufio.NewReader(f)
        }
        return r.f.Read(b)
}

// Alternate pseudo-random implementation for use on
// systems without a reliable /dev/urandom.  So far we
// haven't needed it.

// newReader returns a new pseudorandom generator that
// seeds itself by reading from entropy.  If entropy == nil,
// the generator seeds itself by reading from the system's
// random number generator, typically /dev/random.
// The Read method on the returned reader always returns
// the full amount asked for, or else it returns an error.
//
// The generator uses the X9.31 algorithm with AES-128,
// reseeding after every 1 MB of generated data.
func newReader(entropy io.Reader) io.Reader {
        if entropy == nil {
                entropy = &devReader{name: "/dev/random"}
        }
        return &reader{entropy: entropy}
}

type reader struct {
        mu                   sync.Mutex
        budget               int // number of bytes that can be generated
        cipher               *aes.Cipher
        entropy              io.Reader
        time, seed, dst, key [aes.BlockSize]byte
}

func (r *reader) Read(b []byte) (n int, err error) {
        r.mu.Lock()
        defer r.mu.Unlock()
        n = len(b)

        for len(b) > 0 {
                if r.budget == 0 {
                        _, err := io.ReadFull(r.entropy, r.seed[0:])
                        if err != nil {
                                return n - len(b), err
                        }
                        _, err = io.ReadFull(r.entropy, r.key[0:])
                        if err != nil {
                                return n - len(b), err
                        }
                        r.cipher, err = aes.NewCipher(r.key[0:])
                        if err != nil {
                                return n - len(b), err
                        }
                        r.budget = 1 << 20 // reseed after generating 1MB
                }
                r.budget -= aes.BlockSize

                // ANSI X9.31 (== X9.17) algorithm, but using AES in place of 3DES.
                //
                // single block:
                // t = encrypt(time)
                // dst = encrypt(t^seed)
                // seed = encrypt(t^dst)
                ns := time.Now().UnixNano()
                r.time[0] = byte(ns >> 56)
                r.time[1] = byte(ns >> 48)
                r.time[2] = byte(ns >> 40)
                r.time[3] = byte(ns >> 32)
                r.time[4] = byte(ns >> 24)
                r.time[5] = byte(ns >> 16)
                r.time[6] = byte(ns >> 8)
                r.time[7] = byte(ns)
                r.cipher.Encrypt(r.time[0:], r.time[0:])
                for i := 0; i < aes.BlockSize; i++ {
                        r.dst[i] = r.time[i] ^ r.seed[i]
                }
                r.cipher.Encrypt(r.dst[0:], r.dst[0:])
                for i := 0; i < aes.BlockSize; i++ {
                        r.seed[i] = r.time[i] ^ r.dst[i]
                }
                r.cipher.Encrypt(r.seed[0:], r.seed[0:])

                m := copy(b, r.dst[0:])
                b = b[m:]
        }

        return n, nil
}