I'm trying to sign data using the WebCrypto API, but instead of creating a private/public key and exporting it to pkcs#1 or 8, I would really like to use a user's PKCS#12 to sign data. I've read the W3C spec, but cannot make much of it and can't find any good material on how to do this. Right now I want to leave ActiveX and Java Applets aside. Is there a way to tweak the following:
var buffer = encode(prompt("Please enter your password"));
//TODO:
//implement a prompt for a pfx or cert
return crypto.subtle.importKey("raw", buffer, "PBKDF2", false, usages);
//TODO:
//instead of importing it, ask for the certificate's pass to sign data
//with crypto.subtle.sign
Any pointers?
UPDATE Here's the code I've been working
<script src="forge.min.js"></script>
<script>
var errorsReportedByVerifier;
errorsReportedByVerifier = checkStorage() && checkBrowserAPIs();
if (!errorsReportedByVerifier){
console.log("adding click event");
document.getElementById('btnPfx').addEventListener('click', handlePFXFile, false);
storeVariables();
getVariables();
}
function handlePFXFile(evnt) {
console.log("handling pfx")
//alert(document.getElementById('pfx').value);
//error happens in 1st line
//error object does not accept property replace
//forge.min.js Line 1, Column: 17823
var p12Der = forge.util.decode64(document.getElementById('pfx').valueOf());
//var pkcs12Asn1 = forge.asn1.fromDer(p12Der);
//var pkcs12 = forge.pkcs12.pkcs12FromAsn1(pkcs12Asn1, false, 'pss');
console.log("pkcs12");
}
</script>
Web cryptography api does not support PKCS # 12. You can use a third party library to decode the p12 as forge https://github.com/digitalbazaar/forge#pkcs12 and load privateKey in webcrypto
Reading the PKCS#12 certificate
PKCS#12 is stored in DER, so first read it from a File or use a pre-stored base64
//Reading certificate from a 'file' form field
var reader = new FileReader();
reader.onload = function(e) {
var contents = e.target.result;
var pkcs12Der = arrayBufferToString(contents)
var pkcs12B64 = forge.util.encode64(pkcs12Der);
//do something else...
}
reader.readAsArrayBuffer(file);
function arrayBufferToString( buffer ) {
var binary = '';
var bytes = new Uint8Array( buffer );
var len = bytes.byteLength;
for (var i = 0; i < len; i++) {
binary += String.fromCharCode( bytes[ i ] );
}
return binary;
}
//p12 certificate stored in Base64 format
var pkcs12Der= forge.util.decode64(pkcs12B64);
Decode PKCS#12 with forge and extract private key
Then decode DER format to ASN1, and let forge reads the content
var pkcs12Asn1 = forge.asn1.fromDer(pkcs12Der);
var pkcs12 = forge.pkcs12.pkcs12FromAsn1(pkcs12Asn1, false, password);
Then get the private key from pkcs12
of the desired certificate (see forge doc) and convert to PKCS # 8 to be imported with webcrypto
// load keypair and cert chain from safe content(s)
for(var sci = 0; sci < pkcs12.safeContents.length; ++sci) {
var safeContents = pkcs12.safeContents[sci];
for(var sbi = 0; sbi < safeContents.safeBags.length; ++sbi) {
var safeBag = safeContents.safeBags[sbi];
// this bag has a private key
if(safeBag.type === forge.pki.oids.keyBag) {
//Found plain private key
privateKey = safeBag.key;
} else if(safeBag.type === forge.pki.oids.pkcs8ShroudedKeyBag) {
// found encrypted private key
privateKey = safeBag.key;
} else if(safeBag.type === forge.pki.oids.certBag) {
// this bag has a certificate...
}
}
}
Convert to PKCS#8
function _privateKeyToPkcs8(privateKey) {
var rsaPrivateKey = forge.pki.privateKeyToAsn1(privateKey);
var privateKeyInfo = forge.pki.wrapRsaPrivateKey(rsaPrivateKey);
var privateKeyInfoDer = forge.asn1.toDer(privateKeyInfo).getBytes();
var privateKeyInfoDerBuff = stringToArrayBuffer(privateKeyInfoDer);
return privateKeyInfoDerBuff;
}
function stringToArrayBuffer(data){
var arrBuff = new ArrayBuffer(data.length);
var writer = new Uint8Array(arrBuff);
for (var i = 0, len = data.length; i < len; i++) {
writer[i] = data.charCodeAt(i);
}
return arrBuff;
}
Import key in Webcrypto
And finally import the key in webcrypto
function _importCryptoKeyPkcs8(privateKey,extractable) {
var privateKeyInfoDerBuff = _privateKeyToPkcs8(privateKey);
//Import the webcrypto key
return crypto.subtle.importKey(
'pkcs8',
privateKeyInfoDerBuff,
{ name: "RSASSA-PKCS1-v1_5", hash:{name:"SHA-256"}},
extractable,
["sign"]);
}
_importCryptoKeyPkcs8(entry.privateKey,extractable).
then(function(cryptoKey) {
//your cryptokey is here!!!
});
Digital signature
With the imported cryptoKey returned from the above method you can sign with webcrypto.
var digestToSign = forge.util.decode64(digestToSignB64);
var digestToSignBuf = stringToArrayBuffer(digestToSign);
crypto.subtle.sign(
{name: "RSASSA-PKCS1-v1_5"},
cryptoKey,
digestToSignBuf)
.then(function(signature){
signatureB64 = forge.util.encode64(arrayBufferToString(signature))
});
I include coding from base64 because data conversions are not trivial
In pkc12 you also have the certification chain if you need to build advanced formats like AdES