Exporting a random RSA PublicKey from Java and importing it in JavaScript using Web Crypto

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I am able to transfer a byte array from a Java server to a JavaScript server (is received as an Int32Array). With this, I want to be able to transfer a PublicKey generated in Java and receive it as a CryptoKey in JavaScript.

The RSA Public key is generated in Java like so:

SecureRandom sr = new SecureRandom();
KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");
generator.initialize(2048, sr);
KeyPair kp = generator.generateKeyPair();
PublicKey pKey = kp.getPublic();

What I have tried is to use Key#getEncoded() to get the public key as a byte array, transfer it to JavaScript using the aformenetioned method, and then import it like so:

const subtle = window.crypto.subtle;
await subtle.importKey("spki", array, { name: "RSA-OAEP", hash: "SHA-256" }, false, [ "encrypt" ])

Where "array" is the Int32Array received from the Java server. This does not work however, and I always get a non-descript DOMException stating "Data provided to an operation does not meet requirements". I have done the obvious troubleshooting, checking that the array is the same before and after sending, turning the TypedArray into an ArrayBuffer, encoding and decoding in base64 as a byte sanity check, and trying different algorithms but to no avail.

Some resources:

Here is a sample key#getEncoded() byte array as reported by Java before sending (after sending is Int32Array([...]) with the same contents)

[48, -126, 1, 32, 48, 11, 6, 9, 42, -122, 72, -122, -9, 13, 1, 1, 10, 3, -126, 1, 15, 0, 48, -126, 1, 10, 2, -126, 1, 1, 0, -44, -97, 125, 40, -104, -77, -56, 30, 64, -51, -44, 35, -91, 83, 43, -92, 1, 104, -7, -71, 61, -111, 74, -17, -43, 96, 47, 5, 71, 57, -23, -80, 12, 23, -89, -5, 18, 56, 32, -125, -48, 115, -126, 45, 71, 73, -53, -68, -104, -95, 18, -76, 21, 22, 122, 26, -89, -128, -118, 99, -65, 89, -81, -120, 72, -85, 20, 44, -119, -38, 4, -1, -69, -105, -70, -52, 126, 58, 86, -9, 4, -55, 104, -81, 21, -91, -128, -101, -82, -15, -1, -4, -13, -116, 48, -91, -60, 81, 111, 53, 126, 91, -46, 16, -5, -99, 73, -40, -99, -24, -46, -75, -99, 48, -67, 92, -92, -78, -115, 76, -35, -51, 75, -56, 70, 56, -10, 13, -108, 56, 79, 34, -22, -123, -91, -12, 9, -21, -32, 22, -88, -79, -13, -35, 61, 24, -115, -93, 40, 46, -88, 5, -105, -69, 82, -57, 10, -15, -91, 21, 53, -60, -31, -102, -63, -35, 71, -72, 50, 2, 37, 93, -70, -87, -110, -69, -10, 88, 51, 118, 30, 45, -11, 74, -92, -109, -10, 102, 79, -128, 14, 61, 94, -100, 69, 97, 56, 38, -14, 29, -85, -78, 2, 31, -127, -107, 86, -16, -114, -7, -83, 31, 77, -120, 77, 73, 114, 38, -124, 31, 116, -83, 39, -36, 85, 92, 86, 52, 22, -90, -47, 101, 16, 94, -16, -95, -33, 68, 112, 88, 94, -47, 121, -83, 3, -80, 111, 21, -42, 65, -101, 72, -126, 4, -83, -11, 2, 3, 1, 0, 1]

The same data expressed in hexadecimal

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

Thank you to anybody who takes time to help or reply!

webcrypto-api rsa websocket javascript java
1 Answers

First of all a working solution: The DER encoded X.509/SPKI key generated with Key#getEncoded() is Base64 encoded and then imported to the JavaScript side as follows:

(async () => {
    const subtle = window.crypto.subtle;
    var keyAB = b642ab("MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAuuKRgspvg47d4I3pAzCIWKSim2Rs1QeTVE1Hs+P099PkiuMt5dq5GIaIT1DZTYwJrwtUpxnMcr1TNdWGGfovDLJuIRXUFeST1xOD9+rA4FhVZPO/x6ts2TYKiueEq/qPlXREXw8aVq+msw0nYhHFIAAyrtmj7UR6gD3xxl1ghviIycKqUf7rL98b1d6YkYoNW62aIP/u3cJ5v3Fhnth02Cb02M/fX5gvFKJ3Nj2ARbLygZWbO3U09Vs/hnElxE2k1sKxYRqImJdQM04oQOXVVpafZP7eF9/T+YYDxMLcEKAwH9z0fTt9HaL4gyiDWUT02r6qWF7vI85I1jrPLn71mQIDAQAB")

    var key = await subtle.importKey("spki", new Uint8Array(keyAB), { name: "RSA-OAEP", hash: "SHA-256" }, false, [ "encrypt" ])   
    console.log(key)
})();

function b642ab(base64string){
    return Uint8Array.from(atob(base64string), c => c.charCodeAt(0)).buffer;
}

The problem is caused by the Int32Array type you used. A typed array is an array-like view of an underlying ArrayBuffer. In an Int32Array each element corresponds to 4 bytes.
Since your Int32Array contains the same values as your Key#getEncoded(), the underlying ArrayBuffer contains 4 times as many values and therefore no longer corresponds to the original key.

user_90140970
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