Web Crypto API RSA-OAEP Generate Keys and Perform Encryption/Decryption

by Anish

Posted on Friday september 21, 2018

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

The Web crypto api RSA-OAEP algorithm identifier is used to perform encryption and decryption ordering to the RSAES-OAEP algorithm , using the SHA hash functions defined in this specification and using the mask generation function MGF1.

The Demo

This is the web cryptography api example of performing rsa oaep encryption decryption

webcrypto api RSA-OAEP Javascript example

Generate the RSA-OAEP 2048 bit Keys using SHA-256 Algorithms

window.crypto.subtle.generateKey({
                    name: "RSA-OAEP",
                    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)
                ["encrypt", "decrypt"] //must be ["encrypt", "decrypt"] or ["wrapKey", "unwrapKey"]
            )

Sample Export keys to display the RSA public private key in JWK format (You can skip this step) This is for demo purpose, which i showed in UI.

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;
                    }
                );

RSA-OAEP Encryption Example

window.crypto.subtle.encrypt({
                            name: "RSA-OAEP",
                            iv: iv,
                        },
                        publicKey, //from generateKey or importKey above
                        asciiToUint8Array(plainText) //ArrayBuffer of data you want to encrypt
                    )
                    .then(function(encrypted) {
                        //returns an ArrayBuffer containing the encrypted data
                        document.getElementById("cipherText").value = bytesToHexString(encrypted);
                        document.getElementById("salt").value = bytesToHexString(iv);
                    })
                    .catch(function(err) {
                        console.error(err);
                    });

RSA-OAEP decryption Example

var cipherText = document.getElementById("cipherText").value;
    window.crypto.subtle.decrypt({
                name: "RSA-OAEP",
                iv: iv
            },
            privateKey, //from generateKey or importKey above
            hexStringToUint8Array(cipherText) //ArrayBuffer of the data
        )
        .then(function(decrypted) {
            alert(bytesToASCIIString(decrypted));
        })
        .catch(function(err) {
            console.error(err);
        });

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