/
dedupe.go
66 lines (56 loc) · 2.12 KB
/
dedupe.go
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package api
import (
"crypto/sha1"
"encoding/binary"
)
// Data is a pretty good source of entropy, since
// the LoRaWAN frames are encrypted and therefore each
// message is unique.
//
// However this requires the frames to correctly advance
// the frame counter after every transmission. If mote is
// bugys however, this ID will not change, so we need additional
// entropy. The following fields are also the same on every
// transmission:
//
// 1. Frequency
// 2. Modulation, Coding Rate and Data Rate
// 3. Transmission time window
func ComputeUniqueIdUp(up *AnalyticsUplink, fullPayload []byte) {
var extra []byte
extra = []byte{0, 0, 0, 0, 0, 0}
binary.LittleEndian.PutUint32(extra[0:], uint32(up.Frequency))
binary.LittleEndian.PutUint16(extra[4:], uint16(up.CodingRate))
switch dr := up.DataRate.(type) {
case *AnalyticsUplink_DataRateLoRa:
extraDr := []byte{1, 0, 0, 0, 0}
binary.LittleEndian.PutUint16(extraDr[1:], uint16(dr.DataRateLoRa.Bandwidth))
binary.LittleEndian.PutUint16(extraDr[3:], uint16(dr.DataRateLoRa.SpreadingFactor))
extra = append(extra, extraDr...)
case *AnalyticsUplink_DataRateFSK:
extraDr := []byte{2, 0, 0, 0, 0}
binary.LittleEndian.PutUint32(extraDr[1:], uint32(dr.DataRateFSK))
extra = append(extra, extraDr...)
}
csum := sha1.Sum(append(fullPayload, extra...))
up.UniqueId = csum[:]
}
func ComputeUniqueIdDown(up *AnalyticsDownlink, fullPayload []byte) {
var extra []byte
extra = []byte{0, 0, 0, 0, 0, 0}
binary.LittleEndian.PutUint32(extra[0:], uint32(up.Frequency))
binary.LittleEndian.PutUint16(extra[4:], uint16(up.CodingRate))
switch dr := up.DataRate.(type) {
case *AnalyticsDownlink_DataRateLoRa:
extraDr := []byte{1, 0, 0, 0, 0}
binary.LittleEndian.PutUint16(extraDr[1:], uint16(dr.DataRateLoRa.Bandwidth))
binary.LittleEndian.PutUint16(extraDr[3:], uint16(dr.DataRateLoRa.SpreadingFactor))
extra = append(extra, extraDr...)
case *AnalyticsDownlink_DataRateFSK:
extraDr := []byte{2, 0, 0, 0, 0}
binary.LittleEndian.PutUint32(extraDr[1:], uint32(dr.DataRateFSK))
extra = append(extra, extraDr...)
}
csum := sha1.Sum(append(fullPayload, extra...))
up.UniqueId = csum[:]
}