Node.js crypto.publicDecrypt() Method

The crypto.publicDecrypt() method is used to decrypt the content of the buffer with a key which was previously encrypted using the corresponding private key, i.e. crypto.privateEncrypt() method.

Syntax:

crypto.publicDecrypt( key, buffer )

Parameters: This method accepts two parameters as mentioned above and described below:

• key: It is of type Object, string, Buffer, or KeyObject and contains two parameters which are as follows:
  1. passphrase: It is optional for the private key and it is of type either string or buffer.
  2. padding: It is an optional padding value that is defined in crypto.constants, which can be crypto.constants.RSA_NO_PADDING, or crypto.constants.RSA_PKCS1_PADDING. It is of type crypto.constants.
• buffer It is of type Buffer, TypedArray, or DataView.

Return Type: It returns a new Buffer with the decrypted content.

The below examples illustrate the use of crypto.publicDecrypt() method in Node.js: 

Example 1:

javascript

// Node.js program to demonstrate the
// crypto.publicDecrypt() method

// Including crypto, path, and fs module
const crypto = require('crypto');
const fs = require('fs');
const path = require('path');

// Generating key files
function generateKeyFiles() {

    const keyPair = crypto.generateKeyPairSync('rsa', {
        modulusLength: 520,
        publicKeyEncoding: {
            type: 'spki',
            format: 'pem'
        },
        privateKeyEncoding: {
            type: 'pkcs8',
            format: 'pem',
            cipher: 'aes-256-cbc',
            passphrase: ''
        }
    });

    // Creating public and private key file
    fs.writeFileSync("public_key", keyPair.publicKey);
    fs.writeFileSync("private_key", keyPair.privateKey);
}

// Generate keys
generateKeyFiles();

// Reading private key file
let PRIVKEY = fs.readFileSync(path.join(__dirname,
    'private_key'), 'utf8');

// Reading public key file
let PUBKEY = fs.readFileSync(path.join(__dirname,
    'public_key'), 'utf8');

// Defining my msg
myMSG = "GeeksforGeeks!";
console.log("Original msg is : " + myMSG);

// RSA PRIVATE ENCRYPT -> PUBLIC DECRYPT
function privENC_pubDEC(originMSG) {

    // Encrypting msg with privateEncrypt method
    encmsg = crypto.privateEncrypt(PRIVKEY,
        Buffer.from(originMSG, 'utf8'))
        .toString('base64');

    // Decrypting msg with publicDecrypt method
    msg = crypto.publicDecrypt(PUBKEY,
        Buffer.from(encmsg, 'base64'));

    console.log();

    // Prints encrypted msg
    console.log("Encrypted with private key: "
        + encmsg);

    console.log();

    // Prints decrypted msg
    console.log("Decrypted with public key: "
        + msg.toString());
}

// Calling privENC_pubDEC() method
privENC_pubDEC(myMSG);

Output:

Original msg is : GeeksforGeeks!

Encrypted with private key:
knwqke0ZrpJj1sLtL978OyqBMnJUEAEgTy1qJbyEnJyWbjoQ6hO7f
2FPnVhJnZwpZlxLbFQZCV1GMmr6WWJenFo=

Decrypted with public key: GeeksforGeeks!

Example 2:

javascript

// Node.js program to demonstrate the
// crypto.publicDecrypt() method

// Including the fs and crypto modules
const crypto = require('crypto');
const fs = require('fs');

// Reading the Private Key
privK = fs.readFileSync('priv.key').toString();

// Passing the text to be encrypted
// using private key
let buf = Buffer.from('rishabh', 'utf8');

// Encrypting the text
secretData = crypto.privateEncrypt(privK, buf);

// Printing the encrypted text
console.log(secretData);

// Reading the Public key
pubK = fs.readFileSync('pub.key').toString();

// Decrypting the text using public key
origData = crypto.publicDecrypt(pubK, secretData);

// Printing the original content
console.log(origData);

Output:

// Buffer 27 62 a1 2a 53 8d 0d 52 c7 3f e8 cc 89 42 c6
3e 8e 60 cd d3 57 06 d4 c9 1e 31 ba e6 23 8b 2c 10 be 
c1 fc ed 53 a4 9f f9 e0 5b da 74 d7 c2ca d0 98 f4 ... 
// Buffer 72 69 73 68 61 62 68

Reference: https://nodejs.org/api/crypto.html#crypto_crypto_publicdecrypt_key_buffer