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I am currently implementing the RSA-OAEP encryption on Javascript and decryption at Java.

My javascript code has the following

function stringToArrayBuffer(str){
        var buf = new ArrayBuffer(str.length);
        var bufView = new Uint8Array(buf);
        for (var i=0, strLen=str.length; i<strLen; i++) {
            bufView[i] = str.charCodeAt(i);
        return buf;
function arrayBufferToString(str){
    var byteArray = new Uint8Array(str);
    var byteString = '';
    for(var i=0; i < byteArray.byteLength; i++) {
        byteString += String.fromCodePoint(byteArray[i]);
    return byteString;
function encryptDataWithPublicKey(data, key) {
    data = stringToArrayBuffer(data);
    return window.crypto.subtle.encrypt(
            name: "RSA-OAEP",
            //label: Uint8Array([...]) //optional
        key, //from generateKey or importKey above
        data //ArrayBuffer of data you want to encrypt
var pem = Config.encryption.publicKey;
// fetch the part of the PEM string between header and footer
const pemHeader = "-----BEGIN PUBLIC KEY-----";
const pemFooter = "-----END PUBLIC KEY-----";
const pemContents = pem.substring(pemHeader.length, pem.length - pemFooter.length);               
// base64 decode the string to get the binary data
const binaryDerString = window.atob(pemContents);
// convert from a binary string to an ArrayBuffer
const binaryDer = stringToArrayBuffer(binaryDerString);
window.crypto.subtle.importKey(
                        "spki",
                        binaryDer,
                            name: "RSA-OAEP",
                            hash: { name: "SHA-256" }
                        true,
                        ["encrypt"]
                    ).then(function (publicKey) {
                        encryptDataWithPublicKey(text, publicKey).then((result) => {
                            var rdata = arrayBufferToString(result);
                            resolve(rdata);
                    }).catch(function (err) {
                        console.log(err);
                        reject(err);
I also have a Java function to decrypt the text. Assume "rsaOaepCipherText" is a string text.
Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPPadding");
OAEPParameterSpec oaepParams = new OAEPParameterSpec("SHA-256", "MGF1", new MGF1ParameterSpec("SHA-256"), PSource.PSpecified.DEFAULT);
cipher.init(Cipher.DECRYPT_MODE, getPrivateKey(), oaepParams);
return new String(cipher.doFinal(Base64.decodeBase64(rsaOaepCipherText)), "UTF-8");
However I keep getting decryption error on Java, and currently stuck at this portion, is there any error I have done on my encryption on Javascript?
                A good idea is always (even if you don't need it) to make a decryption-function on the same system/language to test of the provided credentials (password,key,ciphertext, algorithm...) get the original plaintext back. For your question here on SO: please provide a SAMPLE dataset (private/public key in PEM-format [with header/footer line], plaintext and encrypted ciphertext).
– Michael Fehr
                Jul 15, 2020 at 8:21
Ok found it. I forgot to include btoa on the string before send to backend.
it should be
encryptDataWithPublicKey(text, publicKey).then((result) => {
   var rdata = arrayBufferToString(result);
   var rResult = window.btoa(rdata);
   resolve(rResult);
        
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