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