Move attachment/websocket [en|de]cryption to libtextsecure
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/* vim: ts=4:sw=4:expandtab
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 *
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 * This program is free software: you can redistribute it and/or modify
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 * it under the terms of the GNU Lesser General Public License as published by
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 * the Free Software Foundation, either version 3 of the License, or
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 * (at your option) any later version.
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 *
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 * This program is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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 * GNU Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public License
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 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
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 */
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;(function(){
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    'use strict';
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    // Various wrappers around low-level crypto operation for specific functions
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    var verifyMAC = function(data, key, mac) {
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        return axolotl.crypto.sign(key, data).then(function(calculated_mac) {
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            if (!isEqual(calculated_mac, mac, true))
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                throw new Error("Bad MAC");
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        });
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    }
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    window.textsecure = window.textsecure || {};
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    window.textsecure.crypto = {
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        // Decrypts message into a raw string
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        decryptWebsocketMessage: function(message) {
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            var signaling_key = axolotl.api.storage.get("signaling_key"); //TODO: in crypto_storage
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            var aes_key = toArrayBuffer(signaling_key.substring(0, 32));
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            var mac_key = toArrayBuffer(signaling_key.substring(32, 32 + 20));
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            var decodedMessage = message.toArrayBuffer();
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            if (new Uint8Array(decodedMessage)[0] != 1)
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                throw new Error("Got bad version number: " + decodedMessage[0]);
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            var iv = decodedMessage.slice(1, 1 + 16);
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            var ciphertext = decodedMessage.slice(1 + 16, decodedMessage.byteLength - 10);
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            var ivAndCiphertext = decodedMessage.slice(0, decodedMessage.byteLength - 10);
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            var mac = decodedMessage.slice(decodedMessage.byteLength - 10, decodedMessage.byteLength);
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            return verifyMAC(ivAndCiphertext, mac_key, mac).then(function() {
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                return window.axolotl.crypto.decrypt(aes_key, ciphertext, iv);
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            });
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        },
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        decryptAttachment: function(encryptedBin, keys) {
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            var aes_key = keys.slice(0, 32);
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            var mac_key = keys.slice(32, 64);
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            var iv = encryptedBin.slice(0, 16);
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            var ciphertext = encryptedBin.slice(16, encryptedBin.byteLength - 32);
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            var ivAndCiphertext = encryptedBin.slice(0, encryptedBin.byteLength - 32);
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            var mac = encryptedBin.slice(encryptedBin.byteLength - 32, encryptedBin.byteLength);
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            return verifyMAC(ivAndCiphertext, mac_key, mac).then(function() {
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                return window.axolotl.crypto.decrypt(aes_key, ciphertext, iv);
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            });
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        },
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        encryptAttachment: function(plaintext, keys, iv) {
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            var aes_key = keys.slice(0, 32);
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            var mac_key = keys.slice(32, 64);
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            return window.axolotl.crypto.encrypt(aes_key, plaintext, iv).then(function(ciphertext) {
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                var ivAndCiphertext = new Uint8Array(16 + ciphertext.byteLength);
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                ivAndCiphertext.set(new Uint8Array(iv));
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                ivAndCiphertext.set(new Uint8Array(ciphertext), 16);
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                return axolotl.crypto.sign(mac_key, ivAndCiphertext.buffer).then(function(mac) {
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                    var encryptedBin = new Uint8Array(16 + ciphertext.byteLength + 32);
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                    encryptedBin.set(ivAndCiphertext);
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                    encryptedBin.set(new Uint8Array(mac), 16 + ciphertext.byteLength);
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                    return encryptedBin.buffer;
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                });
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            });
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        }
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    };
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})();
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