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use cryptographic random for determining skipped packet numbers

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This commit is contained in:
Marten Seemann 2020-12-15 17:15:20 +07:00
parent 486738981f
commit 6b87198c10
2 changed files with 30 additions and 6 deletions
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31
internal/ackhandler/packet_number_generator.go
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@ -3,7 +3,6 @@ package ackhandler
import (
"crypto/rand"
"encoding/binary"
mrand "math/rand"
"github.com/lucas-clemente/quic-go/internal/protocol"
"github.com/lucas-clemente/quic-go/internal/utils"
@ -34,25 +33,45 @@ func (p *sequentialPacketNumberGenerator) Pop() protocol.PacketNumber {
return next
}
type rng struct {
buf [4]byte
}
func (r *rng) Int31() int32 {
rand.Read(r.buf[:])
return int32(binary.BigEndian.Uint32(r.buf[:]) & ^uint32(1<<31))
}
// copied from the standard library math/rand implementation of Int63n
func (r *rng) Int31n(n int32) int32 {
if n&(n-1) == 0 { // n is power of two, can mask
return r.Int31() & (n - 1)
}
max := int32((1 << 31) - 1 - (1<<31)%uint32(n))
v := r.Int31()
for v > max {
v = r.Int31()
}
return v % n
}
// The skippingPacketNumberGenerator generates the packet number for the next packet
// it randomly skips a packet number every averagePeriod packets (on average).
// It is guaranteed to never skip two consecutive packet numbers.
type skippingPacketNumberGenerator struct {
rand *mrand.Rand
period protocol.PacketNumber
maxPeriod protocol.PacketNumber
next protocol.PacketNumber
nextToSkip protocol.PacketNumber
rng rng
}
var _ packetNumberGenerator = &skippingPacketNumberGenerator{}
func newSkippingPacketNumberGenerator(initial, initialPeriod, maxPeriod protocol.PacketNumber) packetNumberGenerator {
b := make([]byte, 8)
rand.Read(b) // it's not the end of the world if we don't get perfect random here
g := &skippingPacketNumberGenerator{
rand: mrand.New(mrand.NewSource(int64(binary.LittleEndian.Uint64(b)))),
next: initial,
period: initialPeriod,
maxPeriod: maxPeriod,
@ -77,6 +96,6 @@ func (p *skippingPacketNumberGenerator) Pop() protocol.PacketNumber {
func (p *skippingPacketNumberGenerator) generateNewSkip() {
// make sure that there are never two consecutive packet numbers that are skipped
p.nextToSkip = p.next + 2 + protocol.PacketNumber(p.rand.Int63n(int64(2*p.period)))
p.nextToSkip = p.next + 2 + protocol.PacketNumber(p.rng.Int31n(int32(2*p.period)))
p.period = utils.MinPacketNumber(2*p.period, p.maxPeriod)
}