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SSL/TLS version and ciphers

To support testing specific client configurations, k6 allows you to specify a version or range of versions of SSL/TLS that are allowed for a connection. You can as also specify which cipher suites are allowed for that connection.

⚠️ Reg. ciphers and TLS 1.3

Due to limitations in the underlying go implementation, changing the ciphers for TLS 1.3 is not supported and will do nothing.

Limiting SSL/TLS version

To limit the k6 to a specific SSL/TLS version, use a global configuration option:

Limiting to a specific SSL/TLS version
1import http from 'k6/http';
2
3export const options = {
4 tlsVersion: http.TLS_1_2,
5};
6
7export default function () {
8 http.get('https://badssl.com');
9}
You can also accept a range of SSL/TLS versions:
Limiting to a range of SSL/TLS versions
1import http from 'k6/http';
2
3export const options = {
4 tlsVersion: {
5 min: http.SSL_3_0,
6 max: http.TLS_1_2,
7 },
8};
9
10export default function () {
11 http.get('https://badssl.com');
12}

Versions available to choose from

Here's the list of available SSL/TLS versions that you can choose from, ordered from oldest version to latest.

  • http.SSL_3_0
  • http.TLS_1_0
  • http.TLS_1_1
  • http.TLS_1_2

Limiting cipher suites

To limit the cipher suites that k6 is allowed to use, there's a global configuration option. You choose a list of allowed ciphers:

Limiting cipher suites
1import http from 'k6/http';
2
3export const options = {
4 tlsCipherSuites: ['TLS_RSA_WITH_RC4_128_SHA', 'TLS_RSA_WITH_AES_128_GCM_SHA256'],
5};
6
7export default function () {
8 http.get('https://badssl.com');
9}

Checking SSL/TLS version and cipher suite used in requests

You can also check which SSL/TLS version and ciphers were used. To do so, look at the tls_version and tls_cipher_suite response object properties.

Check SSL/TLS version and cipher suite
1import http from 'k6/http';
2import { check } from 'k6';
3
4export default function () {
5 const res = http.get('https://sha256.badssl.com');
6 check(res, {
7 'is TLSv1.2': (r) => r.tls_version === http.TLS_1_2,
8 'is sha256 cipher suite': (r) => r.tls_cipher_suite === 'TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256',
9 });
10}

Cipher suites available to choose from

Here's a list of available SSL/TLS cipher suites:

  • TLS_RSA_WITH_RC4_128_SHA
  • TLS_RSA_WITH_3DES_EDE_CBC_SHA
  • TLS_RSA_WITH_AES_128_CBC_SHA
  • TLS_RSA_WITH_AES_256_CBC_SHA
  • TLS_RSA_WITH_AES_128_GCM_SHA256
  • TLS_RSA_WITH_AES_256_GCM_SHA384
  • TLS_ECDHE_ECDSA_WITH_RC4_128_SHA
  • TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA
  • TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA
  • TLS_ECDHE_RSA_WITH_RC4_128_SHA
  • TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA
  • TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
  • TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA
  • TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
  • TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
  • TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
  • TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384

⚠️ Differences depending on k6 build

This list reflects the available cipher suites in the latest official build. If you are using a custom-built k6, the available cipher suites will depend on the Go version you compiled it with, see https://golang.org/pkg/crypto/tls/#pkg-constants.