SSL/TLS version and ciphers

To support testing specific client configurations, you can 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:

import http from 'k6/http';

export const options = {
  tlsVersion: http.TLS_1_2,
};

export default function () {
  http.get('https://badssl.com');
}

You can also accept a range of SSL/TLS versions:

import http from 'k6/http';

export const options = {
  tlsVersion: {
    min: http.SSL_3_0,
    max: http.TLS_1_2,
  },
};

export default function () {
  http.get('https://badssl.com');
}

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
http.TLS_1_3

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:

import http from 'k6/http';

export const options = {
  tlsCipherSuites: ['TLS_RSA_WITH_RC4_128_SHA', 'TLS_RSA_WITH_AES_128_GCM_SHA256'],
};

export default function () {
  http.get('https://badssl.com');
}

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.

import http from 'k6/http';
import { check } from 'k6';

export default function () {
  const res = http.get('https://sha256.badssl.com');
  check(res, {
    'is TLSv1.2': (r) => r.tls_version === http.TLS_1_2,
    'is sha256 cipher suite': (r) => r.tls_cipher_suite === 'TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256',
  });
}

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.