Node.js crypto.privateEncrypt() Method

The crypto.privateEncrypt() method is used to encrypt the stated content of the buffer with the parameter ‘privateKey’.

Syntax:

crypto.privateEncrypt( privateKey, buffer )

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

• privateKey: It can hold Object, string, Buffer, or KeyObject type of data.
  1. key: It is a ‘PEM’ encoded private key. It is of type string, Buffer, and KeyObject.
  2. passphrase: It is an optional passphrase for the private key which is either string or buffer.
  3. padding It is an optional padding value which 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 contains Buffer, TypedArray, or DataView type of data.

Return Value: It returns a new Buffer with the encrypted content.

Below example illustrate the use of crypto.privateEncrypt() method in Node.js:

Example 1:

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

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

// Using a function generateKeyFiles
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 private key file
    fs.writeFileSync("private_key", keyPair.privateKey);
}

// Generate keys
generateKeyFiles();

// Creating a function to encrypt string
function encryptString (plaintext, privateKeyFile) {
    const privateKey = fs.readFileSync(privateKeyFile, "utf8");

    // privateEncrypt() method with its parameters
    const encrypted = crypto.privateEncrypt(
          privateKey, Buffer.from(plaintext));

    return encrypted.toString("base64");
}

// Defining a text to be encrypted
const plainText = "GfG";

// Defining encrypted text
const encrypted = encryptString(plainText, "./private_key");

// Prints plain text
console.log("Plaintext:", plainText);

// Prints encrypted text
console.log("Encrypted: ", encrypted);

Output:

Plaintext: GfG
Encrypted:  c60eR17GTQFkTI1ipTq5qFbYS58lIQqpDiou2UlYeOUE+u7agbtHvvwKaBpzBx4SvTCh5abpaqmyXCyGcUpGc7s=

Example 2:

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

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

// Using a function generateKeyFiles
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 private key file
    fs.writeFileSync("private_key", keyPair.privateKey);
}

// Generate keys
generateKeyFiles();

// Creating a function to encrypt string
function encryptString (plaintext, privateKeyFile) {
    const privateKey = fs.readFileSync(privateKeyFile, "utf8");

    // privateEncrypt() method with its parameters
    const encrypted = crypto.privateEncrypt(
         privateKey, Buffer.from(plaintext));

    // Returns buffer as its not encoded
    return encrypted;
}

// Defining a text to be encrypted
const plainText = "GfG";

// Defining encrypted text
const encrypted = encryptString(plainText, "./private_key");

// Prints plain text
console.log("Plaintext:", plainText);

// Prints encrypted text
console.log("Encrypted buffer: ", encrypted);

Output:

Plaintext: GfG
Encrypted buffer:  <Buffer 14 e5 84 05 2f b5 59 64
22 d2 19 99 f9 66 e5 18 50 76 27 df 0b e6 9f 50 1d a2
51 6a 93 21 04 7b 8f 50 ba 11 82 fd 3c 6e c0 81 be 58
f9 d6 a6 c7 19 da ... >

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