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Node.js diffieHellman.computeSecret() Method

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  • Last Updated : 10 Jun, 2021

The diffieHellman.computeSecret() method is an inbuilt application programming interface of class DiffieHellman within the crypto module which is used to compute the DiffieHellman (dh) secret key.

Syntax:

diffieHellman.computeSecret(otherPublicKey[, 
        inputEncoding][, outputEncoding])

Parameters: This method accepts the following parameters.

  • otherPublicKey: This method takes the other party’s public key as the first parameter.
  • inputEncoding: Specify the encoding of otherPublicKey. If it is not provided otherPublicKey expected to be Buffer, TypedArray, or DataView.
  • outputEncoding: If it is provided String is returned otherwise Buffer is returned.

Return Value: This method returns the diffieHellman shared secret key.

 

Example 1:

index.js




// Node.js program to demonstrate the
// diffieHellman.computeSecret() method
  
const crypto = require('crypto')
  
// Instance of diffieHellman class...
const alice = crypto.createDiffieHellman(512);
const bob = crypto.createDiffieHellman(
        alice.getPrime(), alice.getGenerator());
  
// Generate otherPublicKey
// Pass 'base64' as encoding parameter
const aliceKey = alice.generateKeys('base64');
const bobKey = bob.generateKeys('base64');
  
// Exchange and generate the secret...
// inputEncoding = 'base64' because otherPublicKey
// is 'base64' encoded
// Return value should be 'hex' encoded because 
// outputEncoding = 'hex' 
const aliceSecret = alice.computeSecret(bobKey, 'base64', 'hex');
const bobSecret = bob.computeSecret(aliceKey, 'base64', 'hex');
  
if( aliceSecret === bobSecret ) 
    console.log(`Symmetric key : ${ aliceSecret }`)

Run the index.js file using the following command:

node index.js

Output:

Symmetric key : da884ccb0e24bf7e748f66998550b
f21f96b887e1f936478cdbc63b7806bd2403fd3aa28e5dbf58
bbabeb6f829dd86453eb0985b5ff593fcf7a8e1da20256b2a

Example 2: Take another example without providing outputEncoding.

index.js




// Node.js program to demonstrate the
// diffieHellman.computeSecret() method
  
const crypto = require('crypto')
  
// Instances of diffieHellman class
const alice = crypto.createDiffieHellman('modp15');
const bob = crypto.createDiffieHellman('modp15');
  
// Pass 'base64' as encoding parameter
const aliceKey = alice.generateKeys('base64');
  
// Pass 'hex' as encoding parameter
const bobKey = bob.generateKeys('hex');
  
// Pass inputEncoding = 'hex' because Bob's key 
// 'hex' encocded
// No outputEncoding provided
// Return Buffer 
const aliceSecret = alice.computeSecret(bobKey, 'hex');
  
// Pass inputEncoding = 'base64' because Alice's
// key 'base64' encocded 
// No outputEncoding provided
// Return Buffer
const bobSecret = bob.computeSecret(aliceKey, 'base64');
  
const isSymmetric = aliceSecret.equals(bobSecret)
  
if ( isSymmetric )
    console.log('Symmetric key : ', aliceSecret)

Run the index.js file using the following command:

node index.js

 

Output:

Symmetric key :  <Buffer 6d 1a 6c 00 34 6c>

Example 3: Another example without providing inputEncoding. Pass inputEncoding as null.

Filename: index.js

Javascript




// Node.js program to demonstrate the
// diffieHellman.computeSecret() method
  
const crypto = require('crypto')
  
// Instances of diffieHellman class
const alice = crypto.createDiffieHellman('modp15');
const bob = crypto.createDiffieHellman('modp15');
  
// Generate Key
alice.generateKeys();
bob.generateKeys();
  
// Compute Secret
// inputEncoding is null
// otherPublicKey expected to be Buffer 
const aliceSecret = alice.computeSecret(
        bob.getPublicKey() , null, 'base64');
  
const bobSecret = bob.computeSecret(
        alice.getPublicKey(), null, 'base64');
  
if (aliceSecret === bobSecret)
    console.log(`Symmetric key : ${ aliceSecret }`)

Run the index.js file using the following command:

node index.js

Output: 

Symmetric key : abLoALX9

Reference:

https://nodejs.org/api/crypto.html#crypto_diffiehellman_computesecret_otherpublickey_inputencoding_outputencoding


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