Node.js x509.checkPrivateKey() Function

The x509.checkPrivateKey() is  an inbuilt application programming interface of class X509Certificate within crypto module which is used to check if the public key for this certificate is consistent with the given private key.

Syntax:

const x509.checkPrivateKey(privateKey)

Parameters: This function takes the private key object as a parameter.

Return Value: This function returns Boolean value true if and only if the public key for this certificate is consistent with the given private key.

How to generate a Public certificate?

Public certificate: Open notepad and copy-paste the following key and save the file as public-cert.pem

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

Example 1:

index.js

// Node.js program to demonstrate the
// x509.checkPrivateKey() function

// Importing crypto module
const {X509Certificate,createPrivateKey} = require('crypto')

// Importing fs module
const fs = require('fs')

// getting object of a PEM encoded X509 Certificate.
const x509 = new X509Certificate
             (fs.readFileSync('public-cert.pem'));

// getting private key object
const key = createPrivateKey
            (fs.readFileSync('private-key.pem'))

// checking if the public key is consistent or not
// by using x509.checkPrivateKey() function
const value = x509.checkPrivateKey(key)

// display the result
if(value)
console.log("public key is consistant")
else
console.log("public key is not consitant")

Run the index.js file using the following command:

node index.js

Output:

public key is consistant

Example 2:

index.js

// Node.js program to demonstrate the
// x509.checkPrivateKey() function

// Importing crypto module
const {X509Certificate,createPrivateKey} = require('crypto')

// Importing fs module
const fs = require('fs')

// display the result
if((new X509Certificate(fs.readFileSync('public-cert.pem')))
    .checkPrivateKey(createPrivateKey(fs.readFileSync('private-key.pem'))))

console.log("public key is consistant")
else
console.log("public key is not consitant")

Run the index.js file using the following command:

node index.js

Output:

public key is consistant

Reference: https://nodejs.org/dist/latest-v15.x/docs/api/crypto.html#crypto_x509_checkprivatekey_privatekey