package util import ( "crypto/rand" "crypto/sha256" "fmt" "io" "math/big" "net" "golang.org/x/crypto/hkdf" ) // DeriveKey derives a key from a secret. // // TODO: decide on a secure key derivation function. func DeriveKey(secret, salt, info []byte, length uint) ([]byte, error) { hkdf := hkdf.New(sha256.New, secret, salt, info) key := make([]byte, length) if _, err := io.ReadFull(hkdf, key); err != nil { return nil, err } return key, nil } // GenerateCertificateSerialNumber generates a random serial number for an X.509 certificate. func GenerateCertificateSerialNumber() (*big.Int, error) { serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128) return rand.Int(rand.Reader, serialNumberLimit) } // GenerateRandomBytes reads length bytes from getrandom(2) if available, /dev/urandom otherwise. func GenerateRandomBytes(length int) ([]byte, error) { nonce := make([]byte, length) if _, err := rand.Read(nonce); err != nil { return nil, err } return nonce, nil } func GetIPAddr() (string, error) { conn, err := net.Dial("udp", "8.8.8.8:80") if err != nil { return "", err } defer conn.Close() localAddr := conn.LocalAddr().(*net.UDPAddr) return localAddr.IP.String(), nil } func GetInterfaceIP(netInterface string) (string, error) { netif, err := net.InterfaceByName(netInterface) if err != nil { return "", fmt.Errorf("could not find interface %s: %w", netInterface, err) } addrs, err := netif.Addrs() if err != nil { return "", fmt.Errorf("could not retrieve interface ip addresses %s: %w", netInterface, err) } for _, addr := range addrs { if ipn, ok := addr.(*net.IPNet); ok { if ip := ipn.IP.To4(); ip != nil { return ip.String(), nil } } } return "", fmt.Errorf("interface %s don't have an ipv4 address", netInterface) }