Web Crypto API RSASSA-PKCS1-v1_5 Generate Keys Sign & verify Message

by Anish

Posted on Monday september 24, 2018

This sample chapter extracted from the book, Cryptography for JavaScript Developers.

The Web crypto api RSASSA-PKCS1-v1_5 algorithm identifier is used to perform signing and verification using the RSASSA-PKCS1-v1_5 algorithm specified in [RFC3447] and using the SHA hash functions defined in this specification.

  • Sign: Perform the signature generation operation
  • Verify: Perform the signature verification operation
  • Generate Key: Generate an RSA key pair, with RSA modulus length equal to the modulusLength attribute of normalizedAlgorithm and RSA public exponent equal to the publicExponent attribute of normalizedAlgorithm

RSASSA-PKCS1-v1_5 Demo

This is the web cryptography api example of performing RSASSA-PKCS1-v1_5 message signing and verifying the signature, for the demo purpose the RSASSA-PKCS1-v1_5 keys are extracted in JWK format

Input Text to Signed
Signature Output (Hex)
RSASSA-PKCS1-v1_5 Public Key (JWK) :
RSASSA-PKCS1-v1_5 Private Key (JWK):

RSASSA-PKCS1-v1_5 Javascript example of using webcrypto api

Generate RSASSA-PKCS1-v1_5 Keys for the signing and verifying purpose, message signing is done through

            name: "RSASSA-PKCS1-v1_5",
            modulusLength: 2048, //can be 1024, 2048, or 4096
            publicExponent: new Uint8Array([0x01, 0x00, 0x01]),
            hash: {name: "SHA-256"}, //can be "SHA-1", "SHA-256", "SHA-384", or "SHA-512"
        true, //whether the key is extractable (i.e. can be used in exportKey)
        ["sign", "verify"] //can be any combination of "sign" and "verify"
    .then(function(key) {

        publicKey = key.publicKey;
        privateKey = key.privateKey;
        // For Demo Purpos Only Exported in JWK format
        window.crypto.subtle.exportKey("jwk", key.publicKey).then(
            function(keydata) {
                publicKeyhold = keydata;
                publicKeyJson = JSON.stringify(publicKeyhold);
                document.getElementById("rsapublic").value = publicKeyJson;

        window.crypto.subtle.exportKey("jwk", key.privateKey).then(
            function(keydata) {
                privateKeyhold = keydata;
                privateKeyJson = JSON.stringify(privateKeyhold);
                document.getElementById("rsaprivate").value = privateKeyJson;

The sign process using the user private key.

                    name: "RSASSA-PKCS1-v1_5",
                privateKey, //from generateKey or importKey above
                asciiToUint8Array(plainText) //ArrayBuffer of data you want to sign
            .then(function(signature) {
                //returns an ArrayBuffer containing the signature
                document.getElementById("cipherText").value = bytesToHexString(signature);
            .catch(function(err) {

    .catch(function(err) {

RSASSA-PKCS1-v1_5 Verify the message signature using the public key

            name: "RSASSA-PKCS1-v1_5",
        publicKey, //from generateKey or importKey above
        hexStringToUint8Array(cipherText), //ArrayBuffer of the data
    .then(function(decrypted) {
        alert("Verified   " + decrypted);
    .catch(function(err) {

Download the sample code here
Next Reading RSA-OAEP generateKey/Encrypt/Decrypt

Thanku for reading !!! Give a Share for Support

Your Support Matters!

Instead of directly asking for donations, I'm thrilled to offer you all nine of my books for just $9 on leanpub By grabbing this bundle you not only help cover my coffee, beer, and Amazon bills but also play a crucial role in advancing and refining this project. Your contribution is indispensable, and I'm genuinely grateful for your involvement in this journey!

Any private key value that you enter or we generate is not stored on this site, this tool is provided via an HTTPS URL to ensure that private keys cannot be stolen, for extra security run this software on your network, no cloud dependency

python Cryptography Topics
For Coffee/ Beer/ Amazon Bill and further development of the project Support by Purchasing, The Modern Cryptography CookBook for Just $9 Coupon Price

Kubernetes for DevOps

Hello Dockerfile

Cryptography for Python Developers

Cryptography for JavaScript Developers

Go lang ryptography for Developers