Web Crypto Api fails to verify signature after converting from string

Question

I am storing my data, including the signature in string format, and after converting the signature to and from strings following the MDN Documentation the verification process fails every time. The relevant code bits are:

const publicKey: CryptoKey = await window.crypto.subtle.importKey("spki", str2ab(window.atob(publicKeyStr)), { name: "RSA-PSS", hash: { name: "SHA-256" } }, false, ["verify"]);
const privateKey: CryptoKey = await window.crypto.subtle.importKey("pkcs8", str2ab(window.atob(privateKeyStr)), { name: "RSA-PSS", hash: { name: "SHA-256" } }, false, ["sign"])
    
if(privateKey && publicKey) {
    try {
        const sign = await window.crypto.subtle.sign({name: "RSA-PSS", saltLength: 32}, privateKey, encodedMessage);
        const signature = window.btoa(String.fromCharCode.apply(null, [...new Uint8Array(sign)])); //the way said signature is stored and I can load it
        const res = await window.crypto.subtle.verify({name: "RSA-PSS", saltLength: 32}, publicKey, str2ab(signature), encodedMessage);
        console.log("Verifying:", signature, publicKey, res);
        return res;
        } catch (error) {
            console.error(error);
            return false;
        }
    }
    return false;

With the str2ab(str) function being:

export function str2ab(str: string): ArrayBuffer {
    const buf = new ArrayBuffer(str.length);
    const bufView = new Uint8Array(buf);
    for (let i = 0, strLen = str.length; i < strLen; i++) {
      bufView[i] = str.charCodeAt(i);
    }
    return buf;
}

And encoded message is new TextEncoder.encode(messageString)

user_9014097 · Answer

You store the Base64 encoded signature, but do not perform a Base64 decoding before verification, i.e. the Base64 decoding must be added. For this, in:

const res = await window.crypto.subtle.verify({name: "RSA-PSS", saltLength: 32}, publicKey, str2ab(signature), encodedMessage);

replace str2ab(signature) with b642ab(signature), where b642ab() performs the Base64 decoding:

(async () => {

    var messageString = "The quick brown fox jumps over the lazy dog";
    var encodedMessage = new TextEncoder().encode(messageString);

    var publicKeyStr = "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAunF5aDa6HCfLMMI/MZLT5hDk304CU+ypFMFiBjowQdUMQKYHZ+fklB7GpLxCatxYJ/hZ7rjfHH3Klq20/Y1EbYDRopyTSfkrTzPzwsX4Ur/l25CtdQldhHCTMgwf/Ev/buBNobfzdZE+Dhdv5lQwKtjI43lDKvAi5kEet2TFwfJcJrBiRJeEcLfVgWTXGRQn7gngWKykUu5rS83eAU1xH9FLojQfyia89/EykiOO7/3UWwd+MATZ9HLjSx2/Lf3g2jr81eifEmYDlri/OZp4OhZu+0Bo1LXloCTe+vmIQ2YCX7EatUOuyQMt2Vwx4uV+d/A3DP6PtMGBKpF8St4iGwIDAQAB";
    var privateKeyStr = "MIIEvgIBADANBgkqhkiG9w0BAQEFAASCBKgwggSkAgEAAoIBAQC6cXloNrocJ8swwj8xktPmEOTfTgJT7KkUwWIGOjBB1QxApgdn5+SUHsakvEJq3Fgn+FnuuN8cfcqWrbT9jURtgNGinJNJ+StPM/PCxfhSv+XbkK11CV2EcJMyDB/8S/9u4E2ht/N1kT4OF2/mVDAq2MjjeUMq8CLmQR63ZMXB8lwmsGJEl4Rwt9WBZNcZFCfuCeBYrKRS7mtLzd4BTXEf0UuiNB/KJrz38TKSI47v/dRbB34wBNn0cuNLHb8t/eDaOvzV6J8SZgOWuL85mng6Fm77QGjUteWgJN76+YhDZgJfsRq1Q67JAy3ZXDHi5X538DcM/o+0wYEqkXxK3iIbAgMBAAECggEASlJj0ExIomKmmBhG8q8SM1s2sWG6gdQMjs6MEeluRT/1c2v79cq2Dum5y/+UBl8x8TUKPKSLpCLs+GXkiVKgHXrFlqoN+OYQArG2EUWzuODwczdYPhhupBXwR3oX4g41k/BsYfQfZBVzBFEJdWrIDLyAUFWNlfdGIj2BTiAoySfyqmamvmW8bsvc8coiGlZ28UC85/Xqx9wOzjeGoRkCH7PcTMlc9F7SxSthwX/k1VBXmNOHa+HzGOgO/W3k1LDqJbq2wKjZTW3iVEg2VodjxgBLMm0MueSGoI6IuaZSPMyFEM3gGvC2+cDBI2SL/amhiTUa/VDlTVw/IKbSuar9uQKBgQDd76M0Po5Lqh8ZhQ3obhFqkfO5EBXy7HUL15cw51kVtwF6Gf/J2HNHjwsg9Nb0eJETTS6bbuVd9bn884JoRS986nVTFNZ4dnjEgKjjQ8GjfzdkpbUxsRLWiIxuOQSpIUZGdMi2ctTTtspvMsDsjRRYdYIQCe/SDsdHGT3vcUCybwKBgQDXDz6iVnY84Fh5iDDVrQOR4lYoxCL/ikCDJjC6y1mjR0eVFdBPQ4j1dDSPU9lahBLby0VyagQCDp/kxQOl0z2zBLRI4I8jUtz9/9KW6ze7U7dQJ7OTfumd5I97OyQOG9XZwKUkRgfyb/PAMBSUSLgosi38f+OC3IN3qlvHFzvxFQKBgQCITpUDEmSczih5qQGIvolN1cRF5j5Ey7t7gXbnXz+Umah7kJpMIvdyfMVOAXJABgi8PQwiBLM0ySXo2LpARjXLV8ilNUggBktYDNktc8DrJMgltayaj3HNd2IglD5rjfc2cKWRgOd7/GlKcHaTEnbreYhfR2sWrWLxJOyoMfuVWwKBgFalCbMV6qU0LfEo8aPlBN8ttVDPVNpntP4h0NgxPXgPK8Pg+gA1UWSy4MouGg/hzkdHaj9ifyLlCX598a5JoT4S0x/ZeVHd/LNI8mtjcRzD6cMde7gdFbpLb5NSjIAyrsIAX4hxvpnqiOYRePkVIz0iLGziiaMbfMwlkrxvm/LRAoGBALPRbtSbE2pPgvOHKHTGPr7gKbmsWVbOcQA8rG801T38W/UPe1XtynMEjzzQ29OaVeQwvUN9+DxFXJ6Yvwj6ih4Wdq109i7Oo1fDnMczOQN9DKch2eNAHrNSOMyLDCBm++wbyHAsS2T0VO8+gzLABviZm5AFCQWfke4LZo5mOS10";

    const publicKey = await window.crypto.subtle.importKey("spki", str2ab(window.atob(publicKeyStr)), { name: "RSA-PSS", hash: { name: "SHA-256" } }, false, ["verify"]);
    const privateKey = await window.crypto.subtle.importKey("pkcs8", str2ab(window.atob(privateKeyStr)), { name: "RSA-PSS", hash: { name: "SHA-256" } }, false, ["sign"]);

    if(privateKey && publicKey) {
        const sign = await window.crypto.subtle.sign({name: "RSA-PSS", saltLength: 32}, privateKey, encodedMessage);
        const signature = window.btoa(String.fromCharCode.apply(null, [...new Uint8Array(sign)])); //the way said signature is stored and I can load it
        const res = await window.crypto.subtle.verify({name: "RSA-PSS", saltLength: 32}, publicKey, b642ab(signature), encodedMessage);
        console.log("Verifying:", /*signature, publicKey,*/ res);
    }
})();

function b642ab(base64_string){
    return Uint8Array.from(window.atob(base64_string), c => c.charCodeAt(0));
}

function str2ab(str) {
    const buf = new ArrayBuffer(str.length);
    const bufView = new Uint8Array(buf);
    for (let i = 0, strLen = str.length; i < strLen; i++) {
      bufView[i] = str.charCodeAt(i);
    }
    return buf;
}

After this bug is fixed, verification is successfully performed.

Web Crypto Api fails to verify signature after converting from string

1 Answers