Use crypto/rand in randRange and downgrade go version

go.mod

@@ -1,6 +1,6 @@
 module github.com/theodorsm/covert-dtls
 
-go 1.22
+go 1.21
 
 require (
 	github.com/google/gopacket v1.1.19

go.sum

@@ -15,6 +15,7 @@ golang.org/x/mod v0.1.1-0.20191105210325-c90efee705ee/go.mod h1:QqPTAvyqsEbceGzB
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.27.0 h1:5K3Njcw06/l2y9vpGCSdcxWOYHOUk3dVNGDXN+FvAys=
+golang.org/x/net v0.27.0/go.mod h1:dDi0PyhWNoiUOrAS8uXv/vnScO4wnHQO4mj9fn/RytE=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=

pkg/randomize/util.go

@@ -1,11 +1,20 @@
 package randomize
 
 import (
-	"math/rand/v2"
+	"crypto/rand"
+	"math/big"
 )
 
 func randRange(min, max int) int {
-	return rand.IntN(max-min+1) + min
+	bigRandomNumber, err := rand.Int(rand.Reader, big.NewInt(int64(max+1)))
+	if err != nil {
+		panic(err)
+	}
+	randomNumber := int(bigRandomNumber.Int64())
+	if randomNumber < min {
+		return min
+	}
+	return randomNumber
 }
 
 var ALPNS = []string{"http/1.0", "http/1.1", "h2c", "h2", "h3", "stun.turn", "webrtc", "c-webrtc", "ftp", "pop3", "imap", "mqtt", "smb", "irc", "sip/2"}