Code Examples
package main
import (
"crypto/tls"
"log"
"net/http"
"net/http/httptest"
"os"
)
// zeroSource is an io.Reader that returns an unlimited number of zero bytes.
type zeroSource struct{}
func (zeroSource) Read(b []byte) (n int, err error) {
for i := range b {
b[i] = 0
}
return len(b), nil
}
func main() {
// Debugging TLS applications by decrypting a network traffic capture.
// WARNING: Use of KeyLogWriter compromises security and should only be
// used for debugging.
// Dummy test HTTP server for the example with insecure random so output is
// reproducible.
server := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
server.TLS = &tls.Config{
Rand: zeroSource{}, // for example only; don't do this.
}
server.StartTLS()
defer server.Close()
// Typically the log would go to an open file:
// w, err := os.OpenFile("tls-secrets.txt", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
w := os.Stdout
client := &http.Client{
Transport: &http.Transport{
TLSClientConfig: &tls.Config{
KeyLogWriter: w,
Rand: zeroSource{}, // for reproducible output; don't do this.
InsecureSkipVerify: true, // test server certificate is not trusted.
},
},
}
resp, err := client.Get(server.URL)
if err != nil {
log.Fatalf("Failed to get URL: %v", err)
}
resp.Body.Close()
// The resulting file can be used with Wireshark to decrypt the TLS
// connection by setting (Pre)-Master-Secret log filename in SSL Protocol
// preferences.
}
package main
import (
"crypto/tls"
"crypto/x509"
)
func main() {
// VerifyConnection can be used to replace and customize connection
// verification. This example shows a VerifyConnection implementation that
// will be approximately equivalent to what crypto/tls does normally to
// verify the peer's certificate.
// Client side configuration.
_ = &tls.Config{
// Set InsecureSkipVerify to skip the default validation we are
// replacing. This will not disable VerifyConnection.
InsecureSkipVerify: true,
VerifyConnection: func(cs tls.ConnectionState) error {
opts := x509.VerifyOptions{
DNSName: cs.ServerName,
Intermediates: x509.NewCertPool(),
}
for _, cert := range cs.PeerCertificates[1:] {
opts.Intermediates.AddCert(cert)
}
_, err := cs.PeerCertificates[0].Verify(opts)
return err
},
}
// Server side configuration.
_ = &tls.Config{
// Require client certificates (or VerifyConnection will run anyway and
// panic accessing cs.PeerCertificates[0]) but don't verify them with the
// default verifier. This will not disable VerifyConnection.
ClientAuth: tls.RequireAnyClientCert,
VerifyConnection: func(cs tls.ConnectionState) error {
opts := x509.VerifyOptions{
DNSName: cs.ServerName,
Intermediates: x509.NewCertPool(),
KeyUsages: []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth},
}
for _, cert := range cs.PeerCertificates[1:] {
opts.Intermediates.AddCert(cert)
}
_, err := cs.PeerCertificates[0].Verify(opts)
return err
},
}
// Note that when certificates are not handled by the default verifier
// ConnectionState.VerifiedChains will be nil.
}
package main
import (
"crypto/tls"
"crypto/x509"
)
func main() {
// Connecting with a custom root-certificate set.
const rootPEM = `
-- GlobalSign Root R2, valid until Dec 15, 2021
-----BEGIN CERTIFICATE-----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==
-----END CERTIFICATE-----`
// First, create the set of root certificates. For this example we only
// have one. It's also possible to omit this in order to use the
// default root set of the current operating system.
roots := x509.NewCertPool()
ok := roots.AppendCertsFromPEM([]byte(rootPEM))
if !ok {
panic("failed to parse root certificate")
}
conn, err := tls.Dial("tcp", "mail.google.com:443", &tls.Config{
RootCAs: roots,
})
if err != nil {
panic("failed to connect: " + err.Error())
}
conn.Close()
}
package main
import (
"crypto/tls"
"log"
)
func main() {
cert, err := tls.LoadX509KeyPair("testdata/example-cert.pem", "testdata/example-key.pem")
if err != nil {
log.Fatal(err)
}
cfg := &tls.Config{Certificates: []tls.Certificate{cert}}
listener, err := tls.Listen("tcp", ":2000", cfg)
if err != nil {
log.Fatal(err)
}
_ = listener
}
package main
import (
"crypto/tls"
"log"
)
func main() {
certPem := []byte(`-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----`)
keyPem := []byte(`-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIIrYSSNQFaA2Hwf1duRSxKtLYX5CB04fSeQ6tF1aY/PuoAoGCCqGSM49
AwEHoUQDQgAEPR3tU2Fta9ktY+6P9G0cWO+0kETA6SFs38GecTyudlHz6xvCdz8q
EKTcWGekdmdDPsHloRNtsiCa697B2O9IFA==
-----END EC PRIVATE KEY-----`)
cert, err := tls.X509KeyPair(certPem, keyPem)
if err != nil {
log.Fatal(err)
}
cfg := &tls.Config{Certificates: []tls.Certificate{cert}}
listener, err := tls.Listen("tcp", ":2000", cfg)
if err != nil {
log.Fatal(err)
}
_ = listener
}
package main
import (
"crypto/tls"
"log"
"net/http"
"time"
)
func main() {
certPem := []byte(`-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----`)
keyPem := []byte(`-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIIrYSSNQFaA2Hwf1duRSxKtLYX5CB04fSeQ6tF1aY/PuoAoGCCqGSM49
AwEHoUQDQgAEPR3tU2Fta9ktY+6P9G0cWO+0kETA6SFs38GecTyudlHz6xvCdz8q
EKTcWGekdmdDPsHloRNtsiCa697B2O9IFA==
-----END EC PRIVATE KEY-----`)
cert, err := tls.X509KeyPair(certPem, keyPem)
if err != nil {
log.Fatal(err)
}
cfg := &tls.Config{Certificates: []tls.Certificate{cert}}
srv := &http.Server{
TLSConfig: cfg,
ReadTimeout: time.Minute,
WriteTimeout: time.Minute,
}
log.Fatal(srv.ListenAndServeTLS("", ""))
}
Package-Level Type Names (total 24)
/* sort by: | */
An AlertError is a TLS alert.
When using a QUIC transport, QUICConn methods will return an error
which wraps AlertError rather than sending a TLS alert.( AlertError) Error() string
AlertError : error
A Certificate is a chain of one or more certificates, leaf first.Certificate[][]byte Leaf is the parsed form of the leaf certificate, which may be initialized
using x509.ParseCertificate to reduce per-handshake processing. If nil,
the leaf certificate will be parsed as needed. OCSPStaple contains an optional OCSP response which will be served
to clients that request it. PrivateKey contains the private key corresponding to the public key in
Leaf. This must implement crypto.Signer with an RSA, ECDSA or Ed25519 PublicKey.
For a server up to TLS 1.2, it can also implement crypto.Decrypter with
an RSA PublicKey. SignedCertificateTimestamps contains an optional list of Signed
Certificate Timestamps which will be served to clients that request it. SupportedSignatureAlgorithms is an optional list restricting what
signature algorithms the PrivateKey can be used for.
func LoadX509KeyPair(certFile, keyFile string) (Certificate, error)
func X509KeyPair(certPEMBlock, keyPEMBlock []byte) (Certificate, error)
func (*CertificateRequestInfo).SupportsCertificate(c *Certificate) error
func (*ClientHelloInfo).SupportsCertificate(c *Certificate) error
CertificateRequestInfo contains information from a server's
CertificateRequest message, which is used to demand a certificate and proof
of control from a client. AcceptableCAs contains zero or more, DER-encoded, X.501
Distinguished Names. These are the names of root or intermediate CAs
that the server wishes the returned certificate to be signed by. An
empty slice indicates that the server has no preference. SignatureSchemes lists the signature schemes that the server is
willing to verify. Version is the TLS version that was negotiated for this connection. Context returns the context of the handshake that is in progress.
This context is a child of the context passed to HandshakeContext,
if any, and is canceled when the handshake concludes. SupportsCertificate returns nil if the provided certificate is supported by
the server that sent the CertificateRequest. Otherwise, it returns an error
describing the reason for the incompatibility.
CertificateVerificationError is returned when certificate verification fails during the handshake.Errerror UnverifiedCertificates and its contents should not be modified.(*CertificateVerificationError) Error() string(*CertificateVerificationError) Unwrap() error
*CertificateVerificationError : error
CipherSuite is a TLS cipher suite. Note that most functions in this package
accept and expose cipher suite IDs instead of this type.IDuint16 Insecure is true if the cipher suite has known security issues
due to its primitives, design, or implementation.Namestring Supported versions is the list of TLS protocol versions that can
negotiate this cipher suite.
func CipherSuites() []*CipherSuite
func InsecureCipherSuites() []*CipherSuite
ClientHelloInfo contains information from a ClientHello message in order to
guide application logic in the GetCertificate and GetConfigForClient callbacks. CipherSuites lists the CipherSuites supported by the client (e.g.
TLS_AES_128_GCM_SHA256, TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256). Conn is the underlying net.Conn for the connection. Do not read
from, or write to, this connection; that will cause the TLS
connection to fail. ServerName indicates the name of the server requested by the client
in order to support virtual hosting. ServerName is only set if the
client is using SNI (see RFC 4366, Section 3.1). SignatureSchemes lists the signature and hash schemes that the client
is willing to verify. SignatureSchemes is set only if the Signature
Algorithms Extension is being used (see RFC 5246, Section 7.4.1.4.1). SupportedCurves lists the elliptic curves supported by the client.
SupportedCurves is set only if the Supported Elliptic Curves
Extension is being used (see RFC 4492, Section 5.1.1). SupportedPoints lists the point formats supported by the client.
SupportedPoints is set only if the Supported Point Formats Extension
is being used (see RFC 4492, Section 5.1.2). SupportedProtos lists the application protocols supported by the client.
SupportedProtos is set only if the Application-Layer Protocol
Negotiation Extension is being used (see RFC 7301, Section 3.1).
Servers can select a protocol by setting Config.NextProtos in a
GetConfigForClient return value. SupportedVersions lists the TLS versions supported by the client.
For TLS versions less than 1.3, this is extrapolated from the max
version advertised by the client, so values other than the greatest
might be rejected if used. Context returns the context of the handshake that is in progress.
This context is a child of the context passed to HandshakeContext,
if any, and is canceled when the handshake concludes. SupportsCertificate returns nil if the provided certificate is supported by
the client that sent the ClientHello. Otherwise, it returns an error
describing the reason for the incompatibility.
If this [ClientHelloInfo] was passed to a GetConfigForClient or GetCertificate
callback, this method will take into account the associated [Config]. Note that
if GetConfigForClient returns a different [Config], the change can't be
accounted for by this method.
This function will call x509.ParseCertificate unless c.Leaf is set, which can
incur a significant performance cost.
ClientSessionCache is a cache of ClientSessionState objects that can be used
by a client to resume a TLS session with a given server. ClientSessionCache
implementations should expect to be called concurrently from different
goroutines. Up to TLS 1.2, only ticket-based resumption is supported, not
SessionID-based resumption. In TLS 1.3 they were merged into PSK modes, which
are supported via this interface. Get searches for a ClientSessionState associated with the given key.
On return, ok is true if one was found. Put adds the ClientSessionState to the cache with the given key. It might
get called multiple times in a connection if a TLS 1.3 server provides
more than one session ticket. If called with a nil *ClientSessionState,
it should remove the cache entry.
func NewLRUClientSessionCache(capacity int) ClientSessionCache
ClientSessionState contains the state needed by a client to
resume a previous TLS session. ResumptionState returns the session ticket sent by the server (also known as
the session's identity) and the state necessary to resume this session.
It can be called by [ClientSessionCache.Put] to serialize (with
[SessionState.Bytes]) and store the session.
func NewResumptionState(ticket []byte, state *SessionState) (*ClientSessionState, error)
func ClientSessionCache.Get(sessionKey string) (session *ClientSessionState, ok bool)
func ClientSessionCache.Put(sessionKey string, cs *ClientSessionState)
A Config structure is used to configure a TLS client or server.
After one has been passed to a TLS function it must not be
modified. A Config may be reused; the tls package will also not
modify it. Certificates contains one or more certificate chains to present to the
other side of the connection. The first certificate compatible with the
peer's requirements is selected automatically.
Server configurations must set one of Certificates, GetCertificate or
GetConfigForClient. Clients doing client-authentication may set either
Certificates or GetClientCertificate.
Note: if there are multiple Certificates, and they don't have the
optional field Leaf set, certificate selection will incur a significant
per-handshake performance cost. CipherSuites is a list of enabled TLS 1.0–1.2 cipher suites. The order of
the list is ignored. Note that TLS 1.3 ciphersuites are not configurable.
If CipherSuites is nil, a safe default list is used. The default cipher
suites might change over time. In Go 1.22 RSA key exchange based cipher
suites were removed from the default list, but can be re-added with the
GODEBUG setting tlsrsakex=1. ClientAuth determines the server's policy for
TLS Client Authentication. The default is NoClientCert. ClientCAs defines the set of root certificate authorities
that servers use if required to verify a client certificate
by the policy in ClientAuth. ClientSessionCache is a cache of ClientSessionState entries for TLS
session resumption. It is only used by clients. CurvePreferences contains the elliptic curves that will be used in
an ECDHE handshake, in preference order. If empty, the default will
be used. The client will use the first preference as the type for
its key share in TLS 1.3. This may change in the future. DynamicRecordSizingDisabled disables adaptive sizing of TLS records.
When true, the largest possible TLS record size is always used. When
false, the size of TLS records may be adjusted in an attempt to
improve latency. GetCertificate returns a Certificate based on the given
ClientHelloInfo. It will only be called if the client supplies SNI
information or if Certificates is empty.
If GetCertificate is nil or returns nil, then the certificate is
retrieved from NameToCertificate. If NameToCertificate is nil, the
best element of Certificates will be used.
Once a Certificate is returned it should not be modified. GetClientCertificate, if not nil, is called when a server requests a
certificate from a client. If set, the contents of Certificates will
be ignored.
If GetClientCertificate returns an error, the handshake will be
aborted and that error will be returned. Otherwise
GetClientCertificate must return a non-nil Certificate. If
Certificate.Certificate is empty then no certificate will be sent to
the server. If this is unacceptable to the server then it may abort
the handshake.
GetClientCertificate may be called multiple times for the same
connection if renegotiation occurs or if TLS 1.3 is in use.
Once a Certificate is returned it should not be modified. GetConfigForClient, if not nil, is called after a ClientHello is
received from a client. It may return a non-nil Config in order to
change the Config that will be used to handle this connection. If
the returned Config is nil, the original Config will be used. The
Config returned by this callback may not be subsequently modified.
If GetConfigForClient is nil, the Config passed to Server() will be
used for all connections.
If SessionTicketKey was explicitly set on the returned Config, or if
SetSessionTicketKeys was called on the returned Config, those keys will
be used. Otherwise, the original Config keys will be used (and possibly
rotated if they are automatically managed). InsecureSkipVerify controls whether a client verifies the server's
certificate chain and host name. If InsecureSkipVerify is true, crypto/tls
accepts any certificate presented by the server and any host name in that
certificate. In this mode, TLS is susceptible to machine-in-the-middle
attacks unless custom verification is used. This should be used only for
testing or in combination with VerifyConnection or VerifyPeerCertificate. KeyLogWriter optionally specifies a destination for TLS master secrets
in NSS key log format that can be used to allow external programs
such as Wireshark to decrypt TLS connections.
See https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Key_Log_Format.
Use of KeyLogWriter compromises security and should only be
used for debugging. MaxVersion contains the maximum TLS version that is acceptable.
By default, the maximum version supported by this package is used,
which is currently TLS 1.3. MinVersion contains the minimum TLS version that is acceptable.
By default, TLS 1.2 is currently used as the minimum. TLS 1.0 is the
minimum supported by this package.
The server-side default can be reverted to TLS 1.0 by including the value
"tls10server=1" in the GODEBUG environment variable. NameToCertificate maps from a certificate name to an element of
Certificates. Note that a certificate name can be of the form
'*.example.com' and so doesn't have to be a domain name as such.
Deprecated: NameToCertificate only allows associating a single
certificate with a given name. Leave this field nil to let the library
select the first compatible chain from Certificates. NextProtos is a list of supported application level protocols, in
order of preference. If both peers support ALPN, the selected
protocol will be one from this list, and the connection will fail
if there is no mutually supported protocol. If NextProtos is empty
or the peer doesn't support ALPN, the connection will succeed and
ConnectionState.NegotiatedProtocol will be empty. PreferServerCipherSuites is a legacy field and has no effect.
It used to control whether the server would follow the client's or the
server's preference. Servers now select the best mutually supported
cipher suite based on logic that takes into account inferred client
hardware, server hardware, and security.
Deprecated: PreferServerCipherSuites is ignored. Rand provides the source of entropy for nonces and RSA blinding.
If Rand is nil, TLS uses the cryptographic random reader in package
crypto/rand.
The Reader must be safe for use by multiple goroutines. Renegotiation controls what types of renegotiation are supported.
The default, none, is correct for the vast majority of applications. RootCAs defines the set of root certificate authorities
that clients use when verifying server certificates.
If RootCAs is nil, TLS uses the host's root CA set. ServerName is used to verify the hostname on the returned
certificates unless InsecureSkipVerify is given. It is also included
in the client's handshake to support virtual hosting unless it is
an IP address. SessionTicketKey is used by TLS servers to provide session resumption.
See RFC 5077 and the PSK mode of RFC 8446. If zero, it will be filled
with random data before the first server handshake.
Deprecated: if this field is left at zero, session ticket keys will be
automatically rotated every day and dropped after seven days. For
customizing the rotation schedule or synchronizing servers that are
terminating connections for the same host, use SetSessionTicketKeys. SessionTicketsDisabled may be set to true to disable session ticket and
PSK (resumption) support. Note that on clients, session ticket support is
also disabled if ClientSessionCache is nil. Time returns the current time as the number of seconds since the epoch.
If Time is nil, TLS uses time.Now. UnwrapSession is called on the server to turn a ticket/identity
previously produced by [WrapSession] into a usable session.
UnwrapSession will usually either decrypt a session state in the ticket
(for example with [Config.EncryptTicket]), or use the ticket as a handle
to recover a previously stored state. It must use [ParseSessionState] to
deserialize the session state.
If UnwrapSession returns an error, the connection is terminated. If it
returns (nil, nil), the session is ignored. crypto/tls may still choose
not to resume the returned session. VerifyConnection, if not nil, is called after normal certificate
verification and after VerifyPeerCertificate by either a TLS client
or server. If it returns a non-nil error, the handshake is aborted
and that error results.
If normal verification fails then the handshake will abort before
considering this callback. This callback will run for all connections,
including resumptions, regardless of InsecureSkipVerify or ClientAuth
settings. VerifyPeerCertificate, if not nil, is called after normal
certificate verification by either a TLS client or server. It
receives the raw ASN.1 certificates provided by the peer and also
any verified chains that normal processing found. If it returns a
non-nil error, the handshake is aborted and that error results.
If normal verification fails then the handshake will abort before
considering this callback. If normal verification is disabled (on the
client when InsecureSkipVerify is set, or on a server when ClientAuth is
RequestClientCert or RequireAnyClientCert), then this callback will be
considered but the verifiedChains argument will always be nil. When
ClientAuth is NoClientCert, this callback is not called on the server.
rawCerts may be empty on the server if ClientAuth is RequestClientCert or
VerifyClientCertIfGiven.
This callback is not invoked on resumed connections, as certificates are
not re-verified on resumption.
verifiedChains and its contents should not be modified. WrapSession is called on the server to produce a session ticket/identity.
WrapSession must serialize the session state with [SessionState.Bytes].
It may then encrypt the serialized state (for example with
[Config.DecryptTicket]) and use it as the ticket, or store the state and
return a handle for it.
If WrapSession returns an error, the connection is terminated.
Warning: the return value will be exposed on the wire and to clients in
plaintext. The application is in charge of encrypting and authenticating
it (and rotating keys) or returning high-entropy identifiers. Failing to
do so correctly can compromise current, previous, and future connections
depending on the protocol version. BuildNameToCertificate parses c.Certificates and builds c.NameToCertificate
from the CommonName and SubjectAlternateName fields of each of the leaf
certificates.
Deprecated: NameToCertificate only allows associating a single certificate
with a given name. Leave that field nil to let the library select the first
compatible chain from Certificates. Clone returns a shallow clone of c or nil if c is nil. It is safe to clone a [Config] that is
being used concurrently by a TLS client or server. DecryptTicket decrypts a ticket encrypted by [Config.EncryptTicket]. It can
be used as a [Config.UnwrapSession] implementation.
If the ticket can't be decrypted or parsed, DecryptTicket returns (nil, nil). EncryptTicket encrypts a ticket with the [Config]'s configured (or default)
session ticket keys. It can be used as a [Config.WrapSession] implementation. SetSessionTicketKeys updates the session ticket keys for a server.
The first key will be used when creating new tickets, while all keys can be
used for decrypting tickets. It is safe to call this function while the
server is running in order to rotate the session ticket keys. The function
will panic if keys is empty.
Calling this function will turn off automatic session ticket key rotation.
If multiple servers are terminating connections for the same host they should
all have the same session ticket keys. If the session ticket keys leaks,
previously recorded and future TLS connections using those keys might be
compromised.
func (*Config).Clone() *Config
func Client(conn net.Conn, config *Config) *Conn
func Dial(network, addr string, config *Config) (*Conn, error)
func DialWithDialer(dialer *net.Dialer, network, addr string, config *Config) (*Conn, error)
func Listen(network, laddr string, config *Config) (net.Listener, error)
func NewListener(inner net.Listener, config *Config) net.Listener
func Server(conn net.Conn, config *Config) *Conn
func net/smtp.(*Client).StartTLS(config *Config) error
A Conn represents a secured connection.
It implements the net.Conn interface. Close closes the connection. CloseWrite shuts down the writing side of the connection. It should only be
called once the handshake has completed and does not call CloseWrite on the
underlying connection. Most callers should just use [Conn.Close]. ConnectionState returns basic TLS details about the connection. Handshake runs the client or server handshake
protocol if it has not yet been run.
Most uses of this package need not call Handshake explicitly: the
first [Conn.Read] or [Conn.Write] will call it automatically.
For control over canceling or setting a timeout on a handshake, use
[Conn.HandshakeContext] or the [Dialer]'s DialContext method instead.
In order to avoid denial of service attacks, the maximum RSA key size allowed
in certificates sent by either the TLS server or client is limited to 8192
bits. This limit can be overridden by setting tlsmaxrsasize in the GODEBUG
environment variable (e.g. GODEBUG=tlsmaxrsasize=4096). HandshakeContext runs the client or server handshake
protocol if it has not yet been run.
The provided Context must be non-nil. If the context is canceled before
the handshake is complete, the handshake is interrupted and an error is returned.
Once the handshake has completed, cancellation of the context will not affect the
connection.
Most uses of this package need not call HandshakeContext explicitly: the
first [Conn.Read] or [Conn.Write] will call it automatically. LocalAddr returns the local network address. NetConn returns the underlying connection that is wrapped by c.
Note that writing to or reading from this connection directly will corrupt the
TLS session. OCSPResponse returns the stapled OCSP response from the TLS server, if
any. (Only valid for client connections.) Read reads data from the connection.
As Read calls [Conn.Handshake], in order to prevent indefinite blocking a deadline
must be set for both Read and [Conn.Write] before Read is called when the handshake
has not yet completed. See [Conn.SetDeadline], [Conn.SetReadDeadline], and
[Conn.SetWriteDeadline]. RemoteAddr returns the remote network address. SetDeadline sets the read and write deadlines associated with the connection.
A zero value for t means [Conn.Read] and [Conn.Write] will not time out.
After a Write has timed out, the TLS state is corrupt and all future writes will return the same error. SetReadDeadline sets the read deadline on the underlying connection.
A zero value for t means [Conn.Read] will not time out. SetWriteDeadline sets the write deadline on the underlying connection.
A zero value for t means [Conn.Write] will not time out.
After a [Conn.Write] has timed out, the TLS state is corrupt and all future writes will return the same error. VerifyHostname checks that the peer certificate chain is valid for
connecting to host. If so, it returns nil; if not, it returns an error
describing the problem. Write writes data to the connection.
As Write calls [Conn.Handshake], in order to prevent indefinite blocking a deadline
must be set for both [Conn.Read] and Write before Write is called when the handshake
has not yet completed. See [Conn.SetDeadline], [Conn.SetReadDeadline], and
[Conn.SetWriteDeadline].
*Conn : internal/bisect.Writer
*Conn : io.Closer
*Conn : io.ReadCloser
*Conn : io.Reader
*Conn : io.ReadWriteCloser
*Conn : io.ReadWriter
*Conn : io.WriteCloser
*Conn : io.Writer
*Conn : net.Conn
func Client(conn net.Conn, config *Config) *Conn
func Dial(network, addr string, config *Config) (*Conn, error)
func DialWithDialer(dialer *net.Dialer, network, addr string, config *Config) (*Conn, error)
func Server(conn net.Conn, config *Config) *Conn
ConnectionState records basic TLS details about the connection. CipherSuite is the cipher suite negotiated for the connection (e.g.
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, TLS_AES_128_GCM_SHA256). DidResume is true if this connection was successfully resumed from a
previous session with a session ticket or similar mechanism. HandshakeComplete is true if the handshake has concluded. NegotiatedProtocol is the application protocol negotiated with ALPN. NegotiatedProtocolIsMutual used to indicate a mutual NPN negotiation.
Deprecated: this value is always true. OCSPResponse is a stapled Online Certificate Status Protocol (OCSP)
response provided by the peer for the leaf certificate, if any. PeerCertificates are the parsed certificates sent by the peer, in the
order in which they were sent. The first element is the leaf certificate
that the connection is verified against.
On the client side, it can't be empty. On the server side, it can be
empty if Config.ClientAuth is not RequireAnyClientCert or
RequireAndVerifyClientCert.
PeerCertificates and its contents should not be modified. ServerName is the value of the Server Name Indication extension sent by
the client. It's available both on the server and on the client side. SignedCertificateTimestamps is a list of SCTs provided by the peer
through the TLS handshake for the leaf certificate, if any. TLSUnique contains the "tls-unique" channel binding value (see RFC 5929,
Section 3). This value will be nil for TLS 1.3 connections and for
resumed connections that don't support Extended Master Secret (RFC 7627). VerifiedChains is a list of one or more chains where the first element is
PeerCertificates[0] and the last element is from Config.RootCAs (on the
client side) or Config.ClientCAs (on the server side).
On the client side, it's set if Config.InsecureSkipVerify is false. On
the server side, it's set if Config.ClientAuth is VerifyClientCertIfGiven
(and the peer provided a certificate) or RequireAndVerifyClientCert.
VerifiedChains and its contents should not be modified. Version is the TLS version used by the connection (e.g. VersionTLS12). ExportKeyingMaterial returns length bytes of exported key material in a new
slice as defined in RFC 5705. If context is nil, it is not used as part of
the seed. If the connection was set to allow renegotiation via
Config.Renegotiation, or if the connections supports neither TLS 1.3 nor
Extended Master Secret, this function will return an error.
Exporting key material without Extended Master Secret or TLS 1.3 was disabled
in Go 1.22 due to security issues (see the Security Considerations sections
of RFC 5705 and RFC 7627), but can be re-enabled with the GODEBUG setting
tlsunsafeekm=1.
func (*Conn).ConnectionState() ConnectionState
func (*QUICConn).ConnectionState() ConnectionState
func net/smtp.(*Client).TLSConnectionState() (state ConnectionState, ok bool)
func (*Config).DecryptTicket(identity []byte, cs ConnectionState) (*SessionState, error)
func (*Config).EncryptTicket(cs ConnectionState, ss *SessionState) ([]byte, error)
Dialer dials TLS connections given a configuration and a Dialer for the
underlying connection. Config is the TLS configuration to use for new connections.
A nil configuration is equivalent to the zero
configuration; see the documentation of Config for the
defaults. NetDialer is the optional dialer to use for the TLS connections'
underlying TCP connections.
A nil NetDialer is equivalent to the net.Dialer zero value. Dial connects to the given network address and initiates a TLS
handshake, returning the resulting TLS connection.
The returned [Conn], if any, will always be of type *[Conn].
Dial uses context.Background internally; to specify the context,
use [Dialer.DialContext]. DialContext connects to the given network address and initiates a TLS
handshake, returning the resulting TLS connection.
The provided Context must be non-nil. If the context expires before
the connection is complete, an error is returned. Once successfully
connected, any expiration of the context will not affect the
connection.
The returned [Conn], if any, will always be of type *[Conn].
A QUICConn represents a connection which uses a QUIC implementation as the underlying
transport as described in RFC 9001.
Methods of QUICConn are not safe for concurrent use. Close closes the connection and stops any in-progress handshake. ConnectionState returns basic TLS details about the connection. HandleData handles handshake bytes received from the peer.
It may produce connection events, which may be read with [QUICConn.NextEvent]. NextEvent returns the next event occurring on the connection.
It returns an event with a Kind of [QUICNoEvent] when no events are available. SendSessionTicket sends a session ticket to the client.
It produces connection events, which may be read with [QUICConn.NextEvent].
Currently, it can only be called once. SetTransportParameters sets the transport parameters to send to the peer.
Server connections may delay setting the transport parameters until after
receiving the client's transport parameters. See [QUICTransportParametersRequired]. Start starts the client or server handshake protocol.
It may produce connection events, which may be read with [QUICConn.NextEvent].
Start must be called at most once.
*QUICConn : io.Closer
func QUICClient(config *QUICConfig) *QUICConn
func QUICServer(config *QUICConfig) *QUICConn
A QUICEvent is an event occurring on a QUIC connection.
The type of event is specified by the Kind field.
The contents of the other fields are kind-specific. Set for QUICTransportParameters, QUICSetReadSecret, QUICSetWriteSecret, and QUICWriteData.
The contents are owned by crypto/tls, and are valid until the next NextEvent call.KindQUICEventKind Set for QUICSetReadSecret, QUICSetWriteSecret, and QUICWriteData. Set for QUICSetReadSecret and QUICSetWriteSecret.
func (*QUICConn).NextEvent() QUICEvent
EarlyData specifies whether the ticket may be used for 0-RTT.
func (*QUICConn).SendSessionTicket(opts QUICSessionTicketOptions) error
RecordHeaderError is returned when a TLS record header is invalid. Conn provides the underlying net.Conn in the case that a client
sent an initial handshake that didn't look like TLS.
It is nil if there's already been a handshake or a TLS alert has
been written to the connection. Msg contains a human readable string that describes the error. RecordHeader contains the five bytes of TLS record header that
triggered the error.( RecordHeaderError) Error() string
RecordHeaderError : error
RenegotiationSupport enumerates the different levels of support for TLS
renegotiation. TLS renegotiation is the act of performing subsequent
handshakes on a connection after the first. This significantly complicates
the state machine and has been the source of numerous, subtle security
issues. Initiating a renegotiation is not supported, but support for
accepting renegotiation requests may be enabled.
Even when enabled, the server may not change its identity between handshakes
(i.e. the leaf certificate must be the same). Additionally, concurrent
handshake and application data flow is not permitted so renegotiation can
only be used with protocols that synchronise with the renegotiation, such as
HTTPS.
Renegotiation is not defined in TLS 1.3.
const RenegotiateFreelyAsClient
const RenegotiateNever
const RenegotiateOnceAsClient
A SessionState is a resumable session. EarlyData indicates whether the ticket can be used for 0-RTT in a QUIC
connection. The application may set this to false if it is true to
decline to offer 0-RTT even if supported. Extra is ignored by crypto/tls, but is encoded by [SessionState.Bytes]
and parsed by [ParseSessionState].
This allows [Config.UnwrapSession]/[Config.WrapSession] and
[ClientSessionCache] implementations to store and retrieve additional
data alongside this session.
To allow different layers in a protocol stack to share this field,
applications must only append to it, not replace it, and must use entries
that can be recognized even if out of order (for example, by starting
with an id and version prefix). Bytes encodes the session, including any private fields, so that it can be
parsed by [ParseSessionState]. The encoding contains secret values critical
to the security of future and possibly past sessions.
The specific encoding should be considered opaque and may change incompatibly
between Go versions.
func ParseSessionState(data []byte) (*SessionState, error)
func (*ClientSessionState).ResumptionState() (ticket []byte, state *SessionState, err error)
func (*Config).DecryptTicket(identity []byte, cs ConnectionState) (*SessionState, error)
func NewResumptionState(ticket []byte, state *SessionState) (*ClientSessionState, error)
func (*Config).EncryptTicket(cs ConnectionState, ss *SessionState) ([]byte, error)
CipherSuiteName returns the standard name for the passed cipher suite ID
(e.g. "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256"), or a fallback representation
of the ID value if the cipher suite is not implemented by this package.
CipherSuites returns a list of cipher suites currently implemented by this
package, excluding those with security issues, which are returned by
[InsecureCipherSuites].
The list is sorted by ID. Note that the default cipher suites selected by
this package might depend on logic that can't be captured by a static list,
and might not match those returned by this function.
Client returns a new TLS client side connection
using conn as the underlying transport.
The config cannot be nil: users must set either ServerName or
InsecureSkipVerify in the config.
Dial connects to the given network address using net.Dial
and then initiates a TLS handshake, returning the resulting
TLS connection.
Dial interprets a nil configuration as equivalent to
the zero configuration; see the documentation of Config
for the defaults.
DialWithDialer connects to the given network address using dialer.Dial and
then initiates a TLS handshake, returning the resulting TLS connection. Any
timeout or deadline given in the dialer apply to connection and TLS
handshake as a whole.
DialWithDialer interprets a nil configuration as equivalent to the zero
configuration; see the documentation of [Config] for the defaults.
DialWithDialer uses context.Background internally; to specify the context,
use [Dialer.DialContext] with NetDialer set to the desired dialer.
InsecureCipherSuites returns a list of cipher suites currently implemented by
this package and which have security issues.
Most applications should not use the cipher suites in this list, and should
only use those returned by [CipherSuites].
Listen creates a TLS listener accepting connections on the
given network address using net.Listen.
The configuration config must be non-nil and must include
at least one certificate or else set GetCertificate.
LoadX509KeyPair reads and parses a public/private key pair from a pair
of files. The files must contain PEM encoded data. The certificate file
may contain intermediate certificates following the leaf certificate to
form a certificate chain. On successful return, Certificate.Leaf will
be nil because the parsed form of the certificate is not retained.
NewListener creates a Listener which accepts connections from an inner
Listener and wraps each connection with [Server].
The configuration config must be non-nil and must include
at least one certificate or else set GetCertificate.
NewLRUClientSessionCache returns a [ClientSessionCache] with the given
capacity that uses an LRU strategy. If capacity is < 1, a default capacity
is used instead.
QUICClient returns a new TLS client side connection using QUICTransport as the
underlying transport. The config cannot be nil.
The config's MinVersion must be at least TLS 1.3.
QUICServer returns a new TLS server side connection using QUICTransport as the
underlying transport. The config cannot be nil.
The config's MinVersion must be at least TLS 1.3.
Server returns a new TLS server side connection
using conn as the underlying transport.
The configuration config must be non-nil and must include
at least one certificate or else set GetCertificate.
VersionName returns the name for the provided TLS version number
(e.g. "TLS 1.3"), or a fallback representation of the value if the
version is not implemented by this package.
X509KeyPair parses a public/private key pair from a pair of
PEM encoded data. On successful return, Certificate.Leaf will be nil because
the parsed form of the certificate is not retained.
NoClientCert indicates that no client certificate should be requested
during the handshake, and if any certificates are sent they will not
be verified.
QUICHandshakeDone indicates that the TLS handshake has completed.
QUICNoEvent indicates that there are no events available.
QUICRejectedEarlyData indicates that the server rejected 0-RTT data even
if we offered it. It's returned before QUICEncryptionLevelApplication
keys are returned.
QUICSetReadSecret and QUICSetWriteSecret provide the read and write
secrets for a given encryption level.
QUICEvent.Level, QUICEvent.Data, and QUICEvent.Suite are set.
Secrets for the Initial encryption level are derived from the initial
destination connection ID, and are not provided by the QUICConn.
QUICTransportParameters provides the peer's QUIC transport parameters.
QUICEvent.Data is set.
QUICTransportParametersRequired indicates that the caller must provide
QUIC transport parameters to send to the peer. The caller should set
the transport parameters with QUICConn.SetTransportParameters and call
QUICConn.NextEvent again.
If transport parameters are set before calling QUICConn.Start, the
connection will never generate a QUICTransportParametersRequired event.
QUICWriteData provides data to send to the peer in CRYPTO frames.
QUICEvent.Data is set.
RenegotiateFreelyAsClient allows a remote server to repeatedly
request renegotiation.
RenegotiateNever disables renegotiation.
RenegotiateOnceAsClient allows a remote server to request
renegotiation once per connection.
RequestClientCert indicates that a client certificate should be requested
during the handshake, but does not require that the client send any
certificates.
RequireAndVerifyClientCert indicates that a client certificate should be requested
during the handshake, and that at least one valid certificate is required
to be sent by the client.
RequireAnyClientCert indicates that a client certificate should be requested
during the handshake, and that at least one certificate is required to be
sent by the client, but that certificate is not required to be valid.
VerifyClientCertIfGiven indicates that a client certificate should be requested
during the handshake, but does not require that the client sends a
certificate. If the client does send a certificate it is required to be
valid.
Deprecated: SSLv3 is cryptographically broken, and is no longer
supported by this package. See golang.org/issue/32716.
The pages are generated with Goldsv0.6.9-preview. (GOOS=linux GOARCH=amd64)
Golds is a Go 101 project developed by Tapir Liu.
PR and bug reports are welcome and can be submitted to the issue list.
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