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encrypt-then-mac support

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This commit is contained in:
Kyle Spearrin 2016-12-08 22:21:46 -05:00
parent 264759cfa0
commit 908dc4727c
1 changed files with 65 additions and 9 deletions
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74
src/app/services/cryptoService.js
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@ -5,7 +5,8 @@ angular
var _service = {},
_key,
_b64Key,
_aes;
_aes,
_aesWithMac;
sjcl.beware["CBC mode is dangerous because it doesn't protect message integrity."]();
@ -34,6 +35,16 @@ angular
return _key;
};
_service.getEncKey = function (key) {
key = key || _service.getKey();
return key.slice(0, 4);
};
_service.getMacKey = function (key) {
key = key || _service.getKey();
return key.slice(4);
};
_service.clearKey = function () {
_key = _b64Key = _aes = null;
delete $sessionStorage.key;
@ -70,45 +81,90 @@ angular
return _aes;
};
_service.getAesWithMac = function () {
if (!_aesWithMac && _service.getKey()) {
_aesWithMac = new sjcl.cipher.aes(_service.getEncKey());
}
return _aesWithMac;
};
_service.encrypt = function (plaintextValue, key) {
if (!_service.getKey() && !key) {
throw 'Encryption key unavailable.';
}
if (!key) {
key = _service.getKey();
// TODO: Turn on whenever ready to support encrypt-then-mac
var encKey = null;
if (false) {
encKey = _service.getEncKey(key);
}
else {
encKey = key || _service.getKey();
}
var response = {};
var params = {
mode: "cbc",
mode: 'cbc',
iv: sjcl.random.randomWords(4, 10)
};
var ctJson = sjcl.encrypt(key, plaintextValue, params, response);
var ctJson = sjcl.encrypt(encKey, plaintextValue, params, response);
var ct = ctJson.match(/"ct":"([^"]*)"/)[1];
var iv = sjcl.codec.base64.fromBits(response.iv);
return iv + "|" + ct;
var cipherString = iv + '|' + ct;
// TODO: Turn on whenever ready to support encrypt-then-mac
if (false) {
var mac = computeMac(ct, response.iv);
cipherString = cipherString + '|' + mac;
}
return cipherString;
};
_service.decrypt = function (encValue) {
if (!_service.getAes()) {
if (!_service.getAes() || !_service.getAesWithMac()) {
throw 'AES encryption unavailable.';
}
var encPieces = encValue.split('|');
if (encPieces.length !== 2) {
if (encPieces.length !== 2 && encPieces.length !== 3) {
return '';
}
var ivBits = sjcl.codec.base64.toBits(encPieces[0]);
var ctBits = sjcl.codec.base64.toBits(encPieces[1]);
var decBits = sjcl.mode.cbc.decrypt(_service.getAes(), ctBits, ivBits, null);
var computedMac = null;
if (encPieces.length === 3) {
computedMac = computeMac(ctBits, ivBits);
if (computedMac !== encPieces[2]) {
console.error('MAC failed.');
return '';
}
}
var decBits = sjcl.mode.cbc.decrypt(computedMac ? _service.getAesWithMac() : _service.getAes(), ctBits, ivBits, null);
return sjcl.codec.utf8String.fromBits(decBits);
};
function computeMac(ct, iv) {
if (typeof ct === 'string') {
ct = sjcl.codec.base64.toBits(ct);
}
if (typeof iv === 'string') {
iv = sjcl.codec.base64.toBits(iv);
}
var macKey = _service.getMacKey();
var hmac = new sjcl.misc.hmac(macKey, sjcl.hash.sha256);
var bits = iv.concat(ct);
var mac = hmac.encrypt(bits);
return sjcl.codec.base64.fromBits(mac);
}
return _service;
});