github.com/karalabe/go-ethereum@v0.8.5/crypto/randentropy/rand_entropy.go (about)

     1  package randentropy
     2  
     3  import (
     4  	crand "crypto/rand"
     5  	"encoding/binary"
     6  	"github.com/ethereum/go-ethereum/crypto/sha3"
     7  	"io"
     8  	"os"
     9  	"strings"
    10  	"time"
    11  )
    12  
    13  var Reader io.Reader = &randEntropy{}
    14  
    15  type randEntropy struct {
    16  }
    17  
    18  func (*randEntropy) Read(bytes []byte) (n int, err error) {
    19  	readBytes := GetEntropyMixed(len(bytes))
    20  	copy(bytes, readBytes)
    21  	return len(bytes), nil
    22  }
    23  
    24  // TODO: copied from crypto.go , move to sha3 package?
    25  func Sha3(data []byte) []byte {
    26  	d := sha3.NewKeccak256()
    27  	d.Write(data)
    28  
    29  	return d.Sum(nil)
    30  }
    31  
    32  // TODO: verify. this needs to be audited
    33  // we start with crypt/rand, then XOR in additional entropy from OS
    34  func GetEntropyMixed(n int) []byte {
    35  	startTime := time.Now().UnixNano()
    36  	// for each source, we take SHA3 of the source and use it as seed to math/rand
    37  	// then read bytes from it and XOR them onto the bytes read from crypto/rand
    38  	mainBuff := GetEntropyCSPRNG(n)
    39  	// 1. OS entropy sources
    40  	startTimeBytes := make([]byte, 32)
    41  	binary.PutVarint(startTimeBytes, startTime)
    42  	startTimeHash := Sha3(startTimeBytes)
    43  	mixBytes(mainBuff, startTimeHash)
    44  
    45  	pid := os.Getpid()
    46  	pidBytes := make([]byte, 32)
    47  	binary.PutUvarint(pidBytes, uint64(pid))
    48  	pidHash := Sha3(pidBytes)
    49  	mixBytes(mainBuff, pidHash)
    50  
    51  	osEnv := os.Environ()
    52  	osEnvBytes := []byte(strings.Join(osEnv, ""))
    53  	osEnvHash := Sha3(osEnvBytes)
    54  	mixBytes(mainBuff, osEnvHash)
    55  
    56  	// not all OS have hostname in env variables
    57  	osHostName, err := os.Hostname()
    58  	if err != nil {
    59  		osHostNameBytes := []byte(osHostName)
    60  		osHostNameHash := Sha3(osHostNameBytes)
    61  		mixBytes(mainBuff, osHostNameHash)
    62  	}
    63  	return mainBuff
    64  }
    65  
    66  func GetEntropyCSPRNG(n int) []byte {
    67  	mainBuff := make([]byte, n)
    68  	_, err := io.ReadFull(crand.Reader, mainBuff)
    69  	if err != nil {
    70  		panic("reading from crypto/rand failed: " + err.Error())
    71  	}
    72  	return mainBuff
    73  }
    74  
    75  func mixBytes(buff []byte, mixBuff []byte) []byte {
    76  	bytesToMix := len(buff)
    77  	if bytesToMix > 32 {
    78  		bytesToMix = 32
    79  	}
    80  	for i := 0; i < bytesToMix; i++ {
    81  		buff[i] ^= mixBuff[i]
    82  	}
    83  	return buff
    84  }