privateDecrypt.js
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var parseKeys = require('parse-asn1');
var mgf = require('./mgf');
var xor = require('./xor');
var bn = require('bn.js');
var crt = require('browserify-rsa');
var createHash = require('create-hash');
var withPublic = require('./withPublic');
module.exports = function privateDecrypt(private_key, enc, reverse) {
var padding;
if (private_key.padding) {
padding = private_key.padding;
} else if (reverse) {
padding = 1;
} else {
padding = 4;
}
var key = parseKeys(private_key);
var k = key.modulus.byteLength();
if (enc.length > k || new bn(enc).cmp(key.modulus) >= 0) {
throw new Error('decryption error');
}
var msg;
if (reverse) {
msg = withPublic(new bn(enc), key);
} else {
msg = crt(enc, key);
}
var zBuffer = new Buffer(k - msg.length);
zBuffer.fill(0);
msg = Buffer.concat([zBuffer, msg], k);
if (padding === 4) {
return oaep(key, msg);
} else if (padding === 1) {
return pkcs1(key, msg, reverse);
} else if (padding === 3) {
return msg;
} else {
throw new Error('unknown padding');
}
};
function oaep(key, msg){
var n = key.modulus;
var k = key.modulus.byteLength();
var mLen = msg.length;
var iHash = createHash('sha1').update(new Buffer('')).digest();
var hLen = iHash.length;
var hLen2 = 2 * hLen;
if (msg[0] !== 0) {
throw new Error('decryption error');
}
var maskedSeed = msg.slice(1, hLen + 1);
var maskedDb = msg.slice(hLen + 1);
var seed = xor(maskedSeed, mgf(maskedDb, hLen));
var db = xor(maskedDb, mgf(seed, k - hLen - 1));
if (compare(iHash, db.slice(0, hLen))) {
throw new Error('decryption error');
}
var i = hLen;
while (db[i] === 0) {
i++;
}
if (db[i++] !== 1) {
throw new Error('decryption error');
}
return db.slice(i);
}
function pkcs1(key, msg, reverse){
var p1 = msg.slice(0, 2);
var i = 2;
var status = 0;
while (msg[i++] !== 0) {
if (i >= msg.length) {
status++;
break;
}
}
var ps = msg.slice(2, i - 1);
var p2 = msg.slice(i - 1, i);
if ((p1.toString('hex') !== '0002' && !reverse) || (p1.toString('hex') !== '0001' && reverse)){
status++;
}
if (ps.length < 8) {
status++;
}
if (status) {
throw new Error('decryption error');
}
return msg.slice(i);
}
function compare(a, b){
a = new Buffer(a);
b = new Buffer(b);
var dif = 0;
var len = a.length;
if (a.length !== b.length) {
dif++;
len = Math.min(a.length, b.length);
}
var i = -1;
while (++i < len) {
dif += (a[i] ^ b[i]);
}
return dif;
}