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package randentropy
import (
crand "crypto/rand"
"encoding/binary"
"github.com/ethereum/go-ethereum/crypto/sha3"
"io"
"os"
"strings"
"time"
)
var Reader io.Reader = &randEntropy{}
type randEntropy struct {
}
func (*randEntropy) Read(bytes []byte) (n int, err error) {
readBytes := GetEntropyMixed(len(bytes))
copy(bytes, readBytes)
return len(bytes), nil
}
// TODO: copied from crypto.go , move to sha3 package?
func Sha3(data []byte) []byte {
d := sha3.NewKeccak256()
d.Write(data)
return d.Sum(nil)
}
// TODO: verify. this needs to be audited
// we start with crypt/rand, then XOR in additional entropy from OS
func GetEntropyMixed(n int) []byte {
startTime := time.Now().UnixNano()
// for each source, we take SHA3 of the source and use it as seed to math/rand
// then read bytes from it and XOR them onto the bytes read from crypto/rand
mainBuff := GetEntropyCSPRNG(n)
// 1. OS entropy sources
startTimeBytes := make([]byte, 32)
binary.PutVarint(startTimeBytes, startTime)
startTimeHash := Sha3(startTimeBytes)
mixBytes(mainBuff, startTimeHash)
pid := os.Getpid()
pidBytes := make([]byte, 32)
binary.PutUvarint(pidBytes, uint64(pid))
pidHash := Sha3(pidBytes)
mixBytes(mainBuff, pidHash)
osEnv := os.Environ()
osEnvBytes := []byte(strings.Join(osEnv, ""))
osEnvHash := Sha3(osEnvBytes)
mixBytes(mainBuff, osEnvHash)
// not all OS have hostname in env variables
osHostName, err := os.Hostname()
if err != nil {
osHostNameBytes := []byte(osHostName)
osHostNameHash := Sha3(osHostNameBytes)
mixBytes(mainBuff, osHostNameHash)
}
return mainBuff
}
func GetEntropyCSPRNG(n int) []byte {
mainBuff := make([]byte, n)
_, err := io.ReadFull(crand.Reader, mainBuff)
if err != nil {
panic("reading from crypto/rand failed: " + err.Error())
}
return mainBuff
}
func mixBytes(buff []byte, mixBuff []byte) []byte {
bytesToMix := len(buff)
if bytesToMix > 32 {
bytesToMix = 32
}
for i := 0; i < bytesToMix; i++ {
buff[i] ^= mixBuff[i]
}
return buff
}
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