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path: root/crypto/secp256k1/secp256_rand.go
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package secp256k1

import (
    crand "crypto/rand"
    "io"
    mrand "math/rand"
    "os"
    "strings"
    "time"
)

/*
Note:

- On windows cryto/rand uses CrytoGenRandom which uses RC4 which is insecure
- Android random number generator is known to be insecure.
- Linux uses /dev/urandom , which is thought to be secure and uses entropy pool

Therefore the output is salted.
*/

//finalizer from MurmerHash3
func mmh3f(key uint64) uint64 {
    key ^= key >> 33
    key *= 0xff51afd7ed558ccd
    key ^= key >> 33
    key *= 0xc4ceb9fe1a85ec53
    key ^= key >> 33
    return key
}

//knuth hash
func knuth_hash(in []byte) uint64 {
    var acc uint64 = 3074457345618258791
    for i := 0; i < len(in); i++ {
        acc += uint64(in[i])
        acc *= 3074457345618258799
    }
    return acc
}

var _rand *mrand.Rand

func init() {
    var seed1 uint64 = mmh3f(uint64(time.Now().UnixNano()))
    var seed2 uint64 = knuth_hash([]byte(strings.Join(os.Environ(), "")))
    var seed3 uint64 = mmh3f(uint64(os.Getpid()))

    _rand = mrand.New(mrand.NewSource(int64(seed1 ^ seed2 ^ seed3)))
}

func saltByte(buff []byte) []byte {
    for i := 0; i < len(buff); i++ {
        var v uint64 = uint64(_rand.Int63())
        var b byte
        for j := 0; j < 8; j++ {
            b ^= byte(v & 0xff)
            v = v >> 8
        }
        buff[i] = b
    }
    return buff
}

//On Unix-like systems, Reader reads from /dev/urandom.
//On Windows systems, Reader uses the CryptGenRandom API.

//use entropy pool etc and cryptographic random number generator
//mix in time
//mix in mix in cpu cycle count
func RandByte(n int) []byte {
    buff := make([]byte, n)
    ret, err := io.ReadFull(crand.Reader, buff)
    if len(buff) != ret || err != nil {
        return nil
    }

    buff2 := saltByte(n)
    for i := 0; i < n; i++ {
        buff[i] ^= buff2[2]
    }
    return buff
}

/*
    On Unix-like systems, Reader reads from /dev/urandom.
    On Windows systems, Reader uses the CryptGenRandom API.
*/
func RandByteWeakCrypto(n int) []byte {
    buff := make([]byte, n)
    ret, err := io.ReadFull(crand.Reader, buff)
    if len(buff) != ret || err != nil {
        return nil
    }
    return buff
}