// setInitialSeed sets the initial seed for the Generator. An
// attempt is made to obtain seeds which differ between machines and
// between reboots. To achieve this, the following information is
// incorporated into the seed: the current time of day, account
// information for the current user, and information about the
// installed network interfaces. In addition, if available, random
// bytes from the random number generator in the crypto/rand package
// are used.
func (gen *Generator) setInitialSeed() {
// source 1: system random number generator
buffer := make([]byte, keySize)
n, _ := io.ReadFull(rand.Reader, buffer)
if n > 0 {
trace.T("fortuna/seed", trace.PrioInfo,
"mixing %d bytes from crypto/rand into the seed", n)
gen.Reseed(buffer)
}
// source 2: current time of day
now := time.Now()
trace.T("fortuna/seed", trace.PrioInfo,
"mixing the current time into the seed")
gen.Reseed(int64ToBytes(now.UnixNano()))
// source 3: try different files with timer information, interrupt
// counts, etc.
for _, fname := range []string{"/proc/timer_list", "/proc/stat"} {
buffer, _ = ioutil.ReadFile(fname)
if len(buffer) > 0 {
trace.T("fortuna/seed", trace.PrioInfo,
"mixing %d bytes from %q into the seed", len(buffer), fname)
gen.Reseed(buffer)
}
}
// source 4: user name and login details
user, _ := user.Current()
if user != nil {
trace.T("fortuna/seed", trace.PrioInfo,
"mixing information about the current user into the seed")
gen.Reseed([]byte(user.Uid))
gen.Reseed([]byte(user.Gid))
gen.Reseed([]byte(user.Username))
gen.Reseed([]byte(user.Name))
gen.Reseed([]byte(user.HomeDir))
}
// source 5: network interfaces
ifaces, _ := net.Interfaces()
if ifaces != nil {
trace.T("fortuna/seed", trace.PrioInfo,
"mixing network interface information into the seed")
for _, iface := range ifaces {
gen.ReseedInt64(int64(iface.MTU))
gen.Reseed([]byte(iface.Name))
gen.Reseed(iface.HardwareAddr)
gen.ReseedInt64(int64(iface.Flags))
}
}
}
func (acc *Accumulator) tryReseeding() []byte {
now := time.Now()
acc.poolMutex.Lock()
defer acc.poolMutex.Unlock()
if acc.poolZeroSize >= minPoolSize && now.After(acc.nextReseed) {
acc.nextReseed = now.Add(minReseedInterval)
acc.poolZeroSize = 0
acc.reseedCount++
seed := make([]byte, 0, numPools*sha256d.Size)
pools := []string{}
for i := uint(0); i < numPools; i++ {
x := 1 << i
if acc.reseedCount%x != 0 {
break
}
seed = acc.pool[i].Sum(seed)
acc.pool[i].Reset()
pools = append(pools, strconv.Itoa(int(i)))
}
trace.T("fortuna/seed", trace.PrioInfo,
"reseeding from pools %s", strings.Join(pools, " "))
return seed
}
return nil
}
// NewEntropyTimeStampSink returns a channel through which timing data
// can be submitted to the Accumulator's entropy pools. The current
// time should be written to the returned channel regularly to add
// entropy to the state of the random number generator. The submitted
// times should be chosen such that they cannot be (completely) known
// to an attacker. Typical sources of randomness include the arrival
// times of network packets or the times of key-presses by the user.
//
// The channel can be closed by the caller to indicate that no more
// entropy will be sent via this channel.
func (acc *Accumulator) NewEntropyTimeStampSink() chan<- time.Time {
source := acc.allocateSource()
c := make(chan time.Time, channelBufferSize)
acc.sources.Add(1)
go func() {
defer acc.sources.Done()
seq := uint(0)
lastRequest := time.Now()
loop:
for {
select {
case now, ok := <-c:
if !ok {
break loop
}
dt := now.Sub(lastRequest)
lastRequest = now
trace.T("fortuna/entropy", trace.PrioDebug,
"adding time stamp data from source %d to pool %d",
source, seq%numPools)
acc.addRandomEvent(source, seq, int64ToBytes(int64(dt)))
seq++
case <-acc.stopSources:
break loop
}
}
}()
return c
}
// Reseed uses the current generator state and the given seed value to
// update the generator state. Care is taken to make sure that
// knowledge of the new state after a reseed does not allow to
// reconstruct previous output values of the generator.
//
// This is like the ReseedInt64() method, but the seed is given as a
// byte slice instead of as an int64.
func (gen *Generator) Reseed(seed []byte) {
hash := sha256d.New()
hash.Write(gen.key)
hash.Write(seed)
gen.setKey(hash.Sum(nil))
gen.inc()
trace.T("fortuna/generator", trace.PrioVerbose, "seed updated")
}
// Read and update the seed file.
//
// If the seed file is empty, reading the seed file is omitted. After
// (potentially) reading the contents of the seed file, new seed data
// is written to the file. In case the seed file is corrupted or has
// insecure file permissions, an error is returned.
func (acc *Accumulator) updateSeedFile() error {
fi, err := acc.seedFile.Stat()
if err != nil {
return err
} else if fi.Mode()&os.FileMode(0077) != 0 {
trace.T("fortuna/seed", trace.PrioError,
"seed file %q has insecure permissions, aborted",
acc.seedFile.Name())
return ErrInsecureSeed
}
_, err = acc.seedFile.Seek(0, os.SEEK_SET)
if err != nil {
return err
}
acc.genMutex.Lock()
// To prevent attacks we keep the PRNG locked until the new seed
// file is safely written to disk.
defer acc.genMutex.Unlock()
n := fi.Size()
if n == seedFileSize {
seed := make([]byte, seedFileSize)
_, err := io.ReadFull(acc.seedFile, seed)
if err != nil || isZero(seed) {
trace.T("fortuna/seed", trace.PrioError,
"seed file %q is corrupted, not used: %s",
acc.seedFile.Name(), err)
return ErrCorruptedSeed
}
trace.T("fortuna/seed", trace.PrioInfo,
"mixing %q into the seed", acc.seedFile.Name())
acc.gen.Reseed(seed)
} else if n != 0 {
trace.T("fortuna/seed", trace.PrioError,
"seed file %q has invalid length %d, aborted",
acc.seedFile.Name(), n)
return ErrCorruptedSeed
}
seed := acc.randomDataUnlocked(seedFileSize)
return doWriteSeed(acc.seedFile, seed)
}
func main() {
trace.Register(printTrace, "", trace.PrioDebug)
rng, err := fortuna.NewRNG(seedFileName)
if err != nil {
panic("cannot initialise the RNG: " + err.Error())
}
defer rng.Close()
// entropy source 1: submit some randomness from crypto/rand once a minute
go func() {
sink1 := rng.NewEntropyDataSink()
for _ = range time.Tick(time.Minute) {
buffer := make([]byte, 4)
n, _ := rand.Read(buffer)
sink1 <- buffer[:n]
}
}()
// entropy source 2: submit time between requests
sink2 := rng.NewEntropyTimeStampSink()
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
sink2 <- time.Now()
sizeStr := r.URL.Query().Get("len")
size, _ := strconv.ParseInt(sizeStr, 0, 32)
if size <= 0 {
size = 16
}
w.Header().Set("Content-Length", fmt.Sprintf("%d", size))
io.CopyN(w, rng, size)
trace.T("main", trace.PrioInfo,
"sent %d random bytes for %q", size, r.RequestURI)
})
listenAddr := ":8080"
trace.T("main", trace.PrioInfo,
"listening on http://localhost%s/", listenAddr)
err = http.ListenAndServe(listenAddr, nil)
if err != nil {
trace.T("main", trace.PrioCritical, "%s", err.Error())
}
}
// PseudoRandomData returns a slice of n pseudo-random bytes. The
// result can be used as a replacement for a sequence of n uniformly
// distributed and independent bytes.
func (gen *Generator) PseudoRandomData(n uint) []byte {
numBlocks := gen.numBlocks(n)
res := make([]byte, 0, numBlocks*uint(len(gen.counter)))
for numBlocks > 0 {
count := numBlocks
if count > maxBlocks {
count = maxBlocks
}
res = gen.generateBlocks(res, count)
numBlocks -= count
newKey := gen.generateBlocks(nil, gen.numBlocks(keySize))
gen.setKey(newKey[:keySize])
}
trace.T("fortuna/generator", trace.PrioVerbose,
"generated %d pseudo-random bytes", n)
return res[:n]
}
func doWriteSeed(f *os.File, seed []byte) error {
_, err := f.Seek(0, os.SEEK_SET)
if err != nil {
return err
}
n, err := f.Write(seed)
if err != nil || n != len(seed) {
if err == nil {
err = &os.PathError{Op: "write", Path: f.Name(), Err: nil}
}
return err
}
err = f.Sync()
if err != nil {
return err
}
trace.T("fortuna/seed", trace.PrioInfo,
"writing new seed data to %q", f.Name())
return nil
}
// NewEntropyDataSink returns a channel through which data can be
// submitted to the Accumulator's entropy pools. Data should be
// written to the returned channel periodically to add entropy to the
// state of the random number generator. The written data should be
// derived from quantities which change between calls and which cannot
// be (completely) known to an attacker. Typical sources of
// randomness include noise from a microphone/camera, CPU cycle
// counters, or the number of processes running on the system.
//
// If the data written to the channel is longer than 32 bytes, the
// data is hashed internally and the hash is submitted to the entropy
// pools instead of the data itself.
//
// The channel can be closed by the caller to indicate that no more
// entropy will be sent via this channel.
func (acc *Accumulator) NewEntropyDataSink() chan<- []byte {
source := acc.allocateSource()
c := make(chan []byte, channelBufferSize)
acc.sources.Add(1)
go func() {
defer acc.sources.Done()
seq := uint(0)
loop:
for {
select {
case data, ok := <-c:
if !ok {
break loop
}
if len(data) > 32 {
hash := sha256.New()
hash.Write(data)
data = hash.Sum(nil)
}
trace.T("fortuna/entropy", trace.PrioDebug,
"adding %d bytes from source %d to pool %d",
len(data), source, seq%numPools)
acc.addRandomEvent(source, seq, data)
seq++
case <-acc.stopSources:
break loop
}
}
}()
return c
}