Web Crypto API AES-GCM - generateKey/Encrypt/Decrypt

by Anish

Posted on Monday september 17, 2018

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

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The Crypto interface represents an interface to general purpose cryptographic functionality including a cryptographically strong pseudo-random number generator seeded with truly random values.

The SubtleCrypto.generateKey() method returns a Promise of a newly generated CryptoKey

The Syntax

var result = crypto.subtle.generateKey(algo, extractable, keyUsages);

• algo: Supported algo are: AES-CBC, AES-CTR, AES-GCM, RSA-OAEP, AES-KW, HMAC, RSASSA-PKCS1-v1_5, ECDSA, ECDH, and DH.

• extractable is a Boolean indicating if the key can be extracted from the CryptoKey object at a later stage

• keyUsages is an Array indicating what can be done with the newly generated key. Possible values of the array are for AES encryption:

  • encrypt, allowing the key to be used for encrypting messages.
  • decrypt, allowing the key to be used for decrypting messages.
  • wrapKey, allowing the key to wrap a symmetric key for usage (transfer, storage) in unsecure environments.
  • unwrapKey, allowing the key to unwrap a symmetric key for usage (transfer, storage) in unsecure environments.

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The Demo

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The webcrypto api java script example AES-GCM generateKey Encryption and Decryption

 var iv = crypto.getRandomValues(new Uint8Array(16));
 var secretKey;

window.crypto.subtle.generateKey({
            name: "AES-GCM",
            length: 256, //can be  128, 192, or 256
        },
        false, //whether the key is extractable (i.e. can be used in exportKey)
        ["encrypt", "decrypt"] //can "encrypt", "decrypt" or  "wrapKey", or "unwrapKey"
    ).then(function(key) {
        secretKey = key;
    })
    .catch(function(err) {
        console.error(err);
    });


function AES256_GCM_ENCRYPT() {

    if (secretKey == null) {
        alert("Failed to Generate AES Keys Check The browser Comptabilty ")
        return;
    }

    var plainText = document.getElementById("plainTextGCM").value;

    return crypto.subtle.encrypt({
        name: "aes-gcm",
        iv: iv,
        tagLength: 128 //can be 32, 64, 96, 104, 112, 120 or 128 (default)
    }, secretKey, asciiToUint8Array(plainText)).then(function(cipherText) {
        document.getElementById("cipherTextGCM").value = bytesToHexString(cipherText);
    }, failAndLog);

}

function AES256_GCM_decrypt() {

    if (secretKey == null) {
        alert("Failed to Generate AES Keys Check The browser Comptabilty ")
        return;
    }

    var cipherText = document.getElementById("cipherTextGCM").value;
    crypto.subtle.decrypt({
            name: "aes-gcm",
            iv: iv,
            tagLength: 128 //can be 32, 64, 96, 104, 112, 120 or 128 (default)
        },
        secretKey,
        hexStringToUint8Array(cipherText)
    ).then(
        function(plainText) {
            document.getElementById("resultGCM").innerHTML = "Result: " + bytesToASCIIString(plainText);
        },
        function(result) {
            document.getElementById("resultGCM").innerHTML = "Result: " + result;
        });
}

The HTML

 <div>
    Plain Text: <input type="text" id="plainTextGCM" value="Hello 8gwifi.org">
    <button type="button" onclick="AES256_GCM_ENCRYPT()">AES256-GCM-ENCRYPT</button>
</div>
<div>
    Cipher Text: <input type="text" id="cipherTextGCM" size="50">
    <button type="button" onclick="AES256_GCM_decrypt()">AES256_GCM_decrypt</button>
</div>
<div id="resultGCM">
    Result:
</div>

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Download the sample code here

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Next Reading Perform AES Encryption Using importKey Method

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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

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