Bring us closer to crypto/tls

[daenney]

As part of v2 I'd like us to take some time and see if there's more of crypto/tls we can reuse. Mostly want to ensure we don't diverge from interafces and behaviour in crypto/tls unless mandated by the DTLS RFCs. This should help newcomers to immediately get started with pion/dtls as it's hopefully just swapping out crypto/tls for pion/dtls.

[at-wat]

I have take a look around crypto/tls.
Followings are my suggestion to make pion/dtls closer to crypto/tls

Unexpose or move non-DTLS things

type Closer (#183) ✔️

It is a package internal utility. It would be better to be unexposed.

func GenerateSelfSigned(), func SelfSign() (#183) ✔️

They are for testing and not DTLS specific. It would be better to be unexposed or moved it to somewhere.

func Fingerprint() (#185) ✔️

It looks be a part of SDP more than DTLS. Moving it to pion/sdp would be better.
Not a part of DTLS. (not used in dtls package.)
It is currently used by:

webrtc/quictransport.go:		remoteValue, err := dtls.Fingerprint(remoteCert, hashAlgo)
webrtc/certificate.go:		value, err := dtls.Fingerprint(c.x509Cert, algo)
webrtc/dtlstransport.go:		remoteValue, err := dtls.Fingerprint(remoteCert, hashAlgo)

Interfacing

type Listener (#181) ✔️

type Listener would better be implement net.Listener.
Close(shutdownTimeout time.Duration) differs from net.Listener. Putting shutdownTimeout in Config struct looks better.

Misc.

Clean-up connection timeout config interface

In crypto/tls, TCP connection timeout is configured via Timeout field in net.Dialer. I think adding dtls.DialWithDialer() which is compatible with tls.DialWithDialer() and making default dialer having 30 seconds of default timeout would be clean and good at compatibility with crypto/tls.
It looks unsuitable at now as the package exports dtls.Server and dtls.Client, and DTLS requires timeout also in Server side inside Listener.Accpt() which don't receive Dialer.

[at-wat]

func Fingerprint()

Maybe better to move Fingerprint and also HashAlgorithm under pkg/crypto/?

---

ID of the hash algorithm is TLS specific.

dtls/hash_algorithm.go

Lines 11 to 13 in 0b80bd9

	// HashAlgorithm is used to indicate the hash algorithm used
	// https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-18
	type HashAlgorithm uint16

As a result of looking around the code, I think public APIs would be better to receive crypro.Hash and internally translate to hash ID.

[at-wat]

Behavior

type Listener (#181) ✔️

• Accepted connections should be available after Listener.Close().

type Conn (#184) ✔️

Pass nettest.ConnTest.

• Read should return already buffered data even after the connection is closed.
• SetDeadline should be implemented.

[at-wat]

@daenney @rumpelsepp @jkralik @Sean-Der I have created some PRs to make public APIs more closer to crypto/tls. Please add comments if you have any ideas on them.

[daenney]

I noticed something in the Go 1.14 releases:

• The new CipherSuites and InsecureCipherSuites functions return a list of currently implemented cipher suites
• The new CipherSuiteName function returns a name for a cipher suite ID

Might be nice if we provide these too. CipherSuiteName() can be implemented by calling dtls.cipherSuite.String(), since we already have that one.

CipherSuites and InsecureCipherSuites should return a []tls.CipherSuite which is a bit different from our dtls.cipherSuite. It should be easy to map to those though:

type CipherSuite struct {
    ID   uint16
    Name string

    // Supported versions is the list of TLS protocol versions that can
    // negotiate this cipher suite.
    SupportedVersions []uint16

    // Insecure is true if the cipher suite has known security issues
    // due to its primitives, design, or implementation.
    Insecure bool
}

type cipherSuite interface {
	String() string
	ID() CipherSuiteID
	certificateType() clientCertificateType
	hashFunc() func() hash.Hash
	isPSK() bool
	isInitialized() bool

	// Generate the internal encryption state
	init(masterSecret, clientRandom, serverRandom []byte, isClient bool) error

	encrypt(pkt *recordLayer, raw []byte) ([]byte, error)
	decrypt(in []byte) ([]byte, error)
}

[at-wat]

I think this has been landed, isn't it?

[daenney]

Sure looks like it 🎉.

[at-wat]

🎉