117 lines
4.2 KiB
Go
117 lines
4.2 KiB
Go
package udp
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import (
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"crypto/hmac"
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"encoding/binary"
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"hash"
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"net"
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"time"
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sha256 "github.com/minio/sha256-simd"
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"github.com/chihaya/chihaya/pkg/log"
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)
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// ttl is the duration a connection ID should be valid according to BEP 15.
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const ttl = 2 * time.Minute
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// NewConnectionID creates an 8-byte connection identifier for UDP packets as
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// described by BEP 15.
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// This is a wrapper around creating a new ConnectionIDGenerator and generating
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// an ID. It is recommended to use the generator for performance.
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func NewConnectionID(ip net.IP, now time.Time, key string) []byte {
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return NewConnectionIDGenerator(key).Generate(ip, now)
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}
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// ValidConnectionID determines whether a connection identifier is legitimate.
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// This is a wrapper around creating a new ConnectionIDGenerator and validating
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// the ID. It is recommended to use the generator for performance.
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func ValidConnectionID(connectionID []byte, ip net.IP, now time.Time, maxClockSkew time.Duration, key string) bool {
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return NewConnectionIDGenerator(key).Validate(connectionID, ip, now, maxClockSkew)
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}
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// A ConnectionIDGenerator is a reusable generator and validator for connection
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// IDs as described in BEP 15.
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// It is not thread safe, but is safe to be pooled and reused by other
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// goroutines. It manages its state itself, so it can be taken from and returned
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// to a pool without any cleanup.
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// After initial creation, it can generate connection IDs without allocating.
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// See Generate and Validate for usage notes and guarantees.
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type ConnectionIDGenerator struct {
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// mac is a keyed HMAC that can be reused for subsequent connection ID
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// generations.
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mac hash.Hash
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// connID is an 8-byte slice that holds the generated connection ID after a
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// call to Generate.
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// It must not be referenced after the generator is returned to a pool.
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// It will be overwritten by subsequent calls to Generate.
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connID []byte
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// scratch is a 32-byte slice that is used as a scratchpad for the generated
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// HMACs.
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scratch []byte
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}
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// NewConnectionIDGenerator creates a new connection ID generator.
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func NewConnectionIDGenerator(key string) *ConnectionIDGenerator {
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return &ConnectionIDGenerator{
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mac: hmac.New(sha256.New, []byte(key)),
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connID: make([]byte, 8),
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scratch: make([]byte, 32),
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}
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}
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// reset resets the generator.
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// This is called by other methods of the generator, it's not necessary to call
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// it after getting a generator from a pool.
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func (g *ConnectionIDGenerator) reset() {
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g.mac.Reset()
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g.connID = g.connID[:8]
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g.scratch = g.scratch[:0]
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}
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// Generate generates an 8-byte connection ID as described in BEP 15 for the
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// given IP and the current time.
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//
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// The first 4 bytes of the connection identifier is a unix timestamp and the
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// last 4 bytes are a truncated HMAC token created from the aforementioned
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// unix timestamp and the source IP address of the UDP packet.
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//
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// Truncated HMAC is known to be safe for 2^(-n) where n is the size in bits
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// of the truncated HMAC token. In this use case we have 32 bits, thus a
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// forgery probability of approximately 1 in 4 billion.
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//
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// The generated ID is written to g.connID, which is also returned. g.connID
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// will be reused, so it must not be referenced after returning the generator
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// to a pool and will be overwritten be subsequent calls to Generate!
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func (g *ConnectionIDGenerator) Generate(ip net.IP, now time.Time) []byte {
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g.reset()
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binary.BigEndian.PutUint32(g.connID, uint32(now.Unix()))
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g.mac.Write(g.connID[:4])
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g.mac.Write(ip)
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g.scratch = g.mac.Sum(g.scratch)
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copy(g.connID[4:8], g.scratch[:4])
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log.Debug("generated connection ID", log.Fields{"ip": ip, "now": now, "connID": g.connID})
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return g.connID
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}
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// Validate validates the given connection ID for an IP and the current time.
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func (g *ConnectionIDGenerator) Validate(connectionID []byte, ip net.IP, now time.Time, maxClockSkew time.Duration) bool {
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ts := time.Unix(int64(binary.BigEndian.Uint32(connectionID[:4])), 0)
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log.Debug("validating connection ID", log.Fields{"connID": connectionID, "ip": ip, "ts": ts, "now": now})
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if now.After(ts.Add(ttl)) || ts.After(now.Add(maxClockSkew)) {
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return false
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}
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g.reset()
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g.mac.Write(connectionID[:4])
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g.mac.Write(ip)
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g.scratch = g.mac.Sum(g.scratch)
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return hmac.Equal(g.scratch[:4], connectionID[4:])
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}
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