CryptoKey ArrayBuffer to base64 and Back

Question

I was wondering how do I solve this problem. I generate RSA-OAEP keypair using WebCrypto API, then I export private key in pkcs8 from the keypair which exports as ArrayBuffer and I want to encode this ArrayBuffer into base64 so I can store it as a PEM.

In this testing example I am exporting key as pkcs8 and importing this pkcs8 back to CryptoKey. The problem is that sometimes it works and sometimes it does not.

These are results of the code: NOTE: Only happens one of these states not all at once. NOTE2: This example does not contain -----BEGIN PRIVATE KEY----- prefix and suffix I am only encoding the key.

Case1: Uncaught (in promise) URIError: URI malformed(…)b64DecodeUnicode @ try.php:20b64toab @ try.php:70wayBack @ try.php:66(anonymous function) @ try.php:56

Case2: undefined:1 Uncaught (in promise) DOMException

Case3: OK - works all the way back.

I don't know what causes the errors but I think it has something to do with base64 encoding. As I said sometimes private key generates OK and sometimes not.

Thank you very much for every help in advance.

function b64EncodeUnicode(str) {
    return btoa(encodeURIComponent(str).replace(/%([0-9A-F]{2})/g, function(match, p1) {
        return String.fromCharCode('0x' + p1);
    }));
}

function b64DecodeUnicode(str) {
    return decodeURIComponent(Array.prototype.map.call(atob(str), function(c) {
        return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
    }).join(''));
}

function addNewLines(str) {
    var finalString = '';
    for(var i=0; i < str.length; i++) {
        finalString += str.substring(0, 64) + '\n';
        str = str.substring(64);
    }

     return finalString;
}

window.crypto.subtle.generateKey(
    {
        name: "RSA-OAEP",
        modulusLength: 2048,
        publicExponent: new Uint8Array([0x01, 0x00, 0x01]),
        hash: {name: "SHA-256"}
    },
    true,
    ["encrypt", "decrypt"]
).then(function(keyPair) {
    window.crypto.subtle.exportKey(
        "pkcs8",
        keyPair.privateKey
    ).then(function(exportedPrivateKey) {
        var byteArray = new Uint8Array(exportedPrivateKey);
        console.log(byteArray);
        var byteString = '';
        for(var i=0; i < byteArray.byteLength; i++) {
            byteString += String.fromCodePoint(byteArray[i]);
        }

        wayBack(addNewLines(b64EncodeUnicode(byteString)));
    });
});

function wayBack(pem) {
    var lines = pem.split('\n');
    var encodedString = '';
    for(var i=0; i < lines.length; i++) {
        encodedString += lines[i].trim();
    }
    b64toab(encodedString);
}

function b64toab(b64) {
    var byteString = b64DecodeUnicode(b64);
    console.log(byteString);
    var byteArray = new Uint8Array(byteString.length);
    for(var i=0; i < byteString.length; i++) {
        byteArray[i] = byteString.codePointAt(i);
    }
    console.log(byteArray);

    window.crypto.subtle.importKey(
        "pkcs8",
        byteArray,
        {
            name: "RSA-OAEP",
            hash: {name: "SHA-256"}
        },
        true,
        ["decrypt"]
    ).then(function(importedPrivateKey) {
        console.log(importedPrivateKey);
    });
}

pedrofb · Accepted Answer · 2016-08-02T08:11:02.107

You forgot to include the last part of PEM when you split the string in blocks of 64 characters. Just add finalString += str; to addNewLines

function addNewLines(str) {
    var finalString = '';
    for(var i=0; i < str.length; i++) {
        finalString += str.substring(0, 64) + '\n';
        str = str.substring(64);
    }
    finalString += str;

    return finalString;
}

I have refactorized your example to see what is happening. Use the below code if you consider it useful

function b64EncodeUnicode(str) {
    return btoa(encodeURIComponent(str).replace(/%([0-9A-F]{2})/g, function(match, p1) {
        return String.fromCharCode('0x' + p1);
    }));
}

function b64DecodeUnicode(str) {
    return decodeURIComponent(Array.prototype.map.call(atob(str), function(c) {
        return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
    }).join(''));
}

function addNewLines(str) {
    var finalString = '';
    for(var i=0; i < str.length; i++) {
        finalString += str.substring(0, 64) + '\n';
        str = str.substring(64);
    }
    finalString += str;

    return finalString;
}

function removeLines(pem) {
    var lines = pem.split('\n');
    var encodedString = '';
    for(var i=0; i < lines.length; i++) {
        encodedString += lines[i].trim();
    }
    return encodedString;
}

function stringToArrayBuffer(byteString){
    var byteArray = new Uint8Array(byteString.length);
    for(var i=0; i < byteString.length; i++) {
        byteArray[i] = byteString.codePointAt(i);
    }
    return byteArray;
}

function  arrayBufferToString(exportedPrivateKey){
    var byteArray = new Uint8Array(exportedPrivateKey);
    var byteString = '';
    for(var i=0; i < byteArray.byteLength; i++) {
        byteString += String.fromCodePoint(byteArray[i]);
    }
    return byteString;
}

window.crypto.subtle.generateKey(
    {
        name: "RSA-OAEP",
        modulusLength: 2048,
        publicExponent: new Uint8Array([0x01, 0x00, 0x01]),
        hash: {name: "SHA-256"}
    },
    true,
    ["encrypt", "decrypt"]
).then(function(keyPair) {
    window.crypto.subtle.exportKey(
        "pkcs8",
        keyPair.privateKey
    ).then(function(exportedPrivateKey) {

        var privateKeyDer = arrayBufferToString(exportedPrivateKey); //pkcs#8 to DER
        var privateKeyB64 = b64EncodeUnicode(privateKeyDer); //btoa(privateKeyDer);
        var privateKeyPEMwithLines = addNewLines(privateKeyB64);  //split PEM into 64 character strings
        var privateKeyPEMwithoutLines = removeLines(privateKeyPEMwithLines);  //join PEM
        var privateKeyDerDecoded = b64DecodeUnicode(privateKeyPEMwithoutLines);  // atob(privateKeyB64);
        var privateKeyArrayBuffer = stringToArrayBuffer(privateKeyDerDecoded);  //DER to arrayBuffer
        window.crypto.subtle.importKey(  //importKEy
            "pkcs8",
            privateKeyArrayBuffer,
            {
                name: "RSA-OAEP",
                hash: {name: "SHA-256"}
            },
            true,
            ["decrypt"]
        ).then(function(importedPrivateKey) {
            console.log(importedPrivateKey);
        });
    });
});

Pedro I was wondering if you could review my code, I actually make it working before you posted answer but I am not sure if the solution is correct. I did not include encodeUnicode functions and just used window.btoa & window.atob, I'll post the code as additional answer. I refreshed the page for like 50 times and it worked 100% — Peter Bielak, Aug 02 '16 at 11:06
because I am not sure if it will work all the time for every possible private key that could ever be generated. if .fromCharCode and .charCodeAt will catch everything or if I do have to use .fromCodePoint and .codePointAt and also if unicode encoding is a problem but as far as I know this unicode fix is needed only if you want to display the characters it does not have any effect if I just invisibly encoding it. — Peter Bielak, Aug 02 '16 at 11:16

Peter Bielak · Answer 2 · 2017-02-09T17:47:53.363

I am posting additional working code: (NOTE: Code is without -----BEGIN PRIVATE KEY----- and ----- END PRIVATE KEY ----- base64 only)

function addNewLines(str) {
    var finalString = '';
    while(str.length > 0) {
        finalString += str.substring(0, 64) + '\n';
        str = str.substring(64);
    }

    return finalString;
}

function removeLines(str) {
    return str.replace("\n", "");
}

function arrayBufferToBase64(arrayBuffer) {
    var byteArray = new Uint8Array(arrayBuffer);
    var byteString = '';
    for(var i=0; i < byteArray.byteLength; i++) {
        byteString += String.fromCharCode(byteArray[i]);
    }
    var b64 = window.btoa(byteString);

    return b64;
}

function base64ToArrayBuffer(b64) {
    var byteString = window.atob(b64);
    var byteArray = new Uint8Array(byteString.length);
    for(var i=0; i < byteString.length; i++) {
        byteArray[i] = byteString.charCodeAt(i);
    }

    return byteArray;
}

window.crypto.subtle.generateKey(
    {
        name: "RSA-OAEP",
        modulusLength: 2048,
        publicExponent: new Uint8Array([0x01, 0x00, 0x01]),
        hash: {name: "SHA-256"}
    },
    true,
    ["encrypt", "decrypt"]
).then(function(keyPair) {
    window.crypto.subtle.exportKey(
        "pkcs8",
        keyPair.privateKey
    ).then(function(exportedPrivateKey) {
        var pem = addNewLines(arrayBufferToBase64(exportedPrivateKey));
        importKey(pem);
    });
});

function importKey(b64) {
    b64 = removeLines(b64);
    arrayBuffer = base64ToArrayBuffer(b64);

    window.crypto.subtle.importKey(
        "pkcs8",
        arrayBuffer,
        {
            name: "RSA-OAEP",
            hash: {name: "SHA-256"}
        },
        true,
        ["decrypt"]
    ).then(function(importedPrivateKey) {
        console.log(importedPrivateKey);
    });
}

UPDATE: I wrote a little crypto library that you can use for PEM converting and many more. https://github.com/PeterBielak/OpenCrypto

Usage example:

var crypt = new OpenCrypto();

crypt.getKeyPair().then(function(keyPair) {
    crypt.cryptoPrivateToPem(keyPair.privateKey).then(function(pemPrivateKey) {
        console.log(pemPrivateKey);
    });
});

Hi Peter, this code is simpler, so usually is better. To generate a valid PEM you have to use base64 (without replacing characters). `.atob()` and `.btoa()` works fine except in older IE versions. I usually use `.fromCharCode()` and .`charCodeAt()`. Really I do not know the difference with .fromCodePoint and .codePointAt — pedrofb, Aug 02 '16 at 11:59
Pedro thank you for your review! I'll go with .fromCharCode() and .charCodeAt() functions. http://stackoverflow.com/questions/34680898/can-you-use-string-fromcodepoint-just-like-string-fromcharcode — Peter Bielak, Aug 02 '16 at 12:52

CryptoKey ArrayBuffer to base64 and Back

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