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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')
var Buffer = require('safe-buffer').Buffer
module.exports = function privateDecrypt (privateKey, enc, reverse) {
var padding
if (privateKey.padding) {
padding = privateKey.padding
} else if (reverse) {
padding = 1
} else {
padding = 4
}
var key = parseKeys(privateKey)
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 = Buffer.alloc(k - msg.length)
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 k = key.modulus.byteLength()
var iHash = createHash('sha1').update(Buffer.alloc(0)).digest()
var hLen = iHash.length
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)
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 = Buffer.from(a)
b = Buffer.from(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
}