Wrap and unwrap keys with WebCrypto API

Question

I am using Webcrypto API for some cryptographic work on client-side. Although I cannot wrap and unwrap keys, the browser always returned the following error.

DOMException [OperationError: "The operation failed for an operation-specific reason"

You and I cannot do much with this error, so I pasted my code.

function wrapPrivateKey(privateKey, wrappingKey) {
    var iv = window.crypto.getRandomValues(new Uint8Array(12));
    return window.crypto.subtle.wrapKey(
        "jwk",
        privateKey,
        wrappingKey,
        {
            name: "AES-GCM",
            length: 256,
            iv: iv,
        }
        )
        .then(function (key) {
            return {
                "key": StringToB64(arrayBufferToString(key)),
                "iv": StringToB64(arrayBufferToString(iv))
            };
        })
        .catch(function (err) {
            console.error(err);
            return false;
        });
}

function unwrapPrivateKey(wrappedPrivateKey, unwrappingKey) {
    var obj = JSON.parse(B64ToString(wrappedPrivateKey));
    var key = stringToArrayBuffer(B64ToString(obj["key"]));
    var iv = stringToArrayBuffer(B64ToString(obj["iv"]));
    return window.crypto.subtle.unwrapKey(
        "jwk",
        key,
        unwrappingKey,
        {
            name: "AES-GCM",
            length: 256,
            iv: iv,
        },
        {
            name: "RSA-OAEP",
            hash: {name: "SHA-256"},
        },
        true,
        ["encrypt", "decrypt"]
        )
        .then(function (key) {
            return key;
        })
        .catch(function (err) {
            console.error(err);
            return false;
        });
}

I do not know if the problem is related to converting the key objects to strings. Unfortunately, I need to convert it to a string to persist it in a database.

Answer 1

Here is simple example of key wrapping/unwrapping. This code works in Chrome/Mozilla

const rsaAlg = {
    name: "RSA-OAEP",
    hash: "SHA-256",
    publicExponent: new Uint8Array([1, 0, 1]),
    modulusLength: 2048
};
const aesAlg = {
    name: "AES-GCM",
    length: 256,
    iv: crypto.getRandomValues(new Uint8Array(12)),
};

crypto.subtle.generateKey(rsaAlg, true, ["encrypt", "decrypt"])
    .then((rsaKeys) => {
        return crypto.subtle.generateKey(aesAlg, true, ["encrypt", "decrypt", "wrapKey", "unwrapKey"])
            .then((aesKey) => {
                return crypto.subtle.wrapKey("jwk", rsaKeys.privateKey, aesKey, aesAlg)
                    .then((wrappedKey) => {
                        console.log(wrappedKey); // ArrayBuffer

                        // Unwrap key
                        return crypto.subtle.unwrapKey("jwk", wrappedKey, aesKey, aesAlg, rsaAlg, true, ["decrypt"])
                    })
                    .then((unwrappedKey) => {
                        console.log(unwrappedKey);
                    })
            })
    })
    .catch((err) => {
        console.error(err);
    })

WebCrypto API is different from one browser to another. It would be better to use some modules which allows to fix it webcrypto-shim, webcrypto-liner

Also I see you use var key = stringToArrayBuffer(B64ToString(obj["key"]));. But key must be CryptoKey. If you have raw of symmetric key you have to use importKey function to create CryptoKey from raw