libgocryptfs/cryptfs/nonce.go

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package cryptfs
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import (
"bytes"
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"crypto/rand"
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"encoding/binary"
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"encoding/hex"
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"fmt"
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)
// Get "n" random bytes from /dev/urandom or panic
func RandBytes(n int) []byte {
b := make([]byte, n)
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_, err := rand.Read(b)
if err != nil {
panic("Failed to read random bytes: " + err.Error())
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}
return b
}
// Return a secure random uint64
func RandUint64() uint64 {
b := RandBytes(8)
return binary.BigEndian.Uint64(b)
}
type nonceGenerator struct {
lastNonce []byte
nonceLen int // bytes
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}
// Get a random 96 bit nonce
func (n *nonceGenerator) Get() []byte {
nonce := RandBytes(n.nonceLen)
Debug.Printf("nonceGenerator.Get(): %s\n", hex.EncodeToString(nonce))
if bytes.Equal(nonce, n.lastNonce) {
m := fmt.Sprintf("Got the same nonce twice: %s. This should never happen!", hex.EncodeToString(nonce))
panic(m)
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}
n.lastNonce = nonce
return nonce
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}