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reduce buffer creation for ctr mode #48

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merged 1 commit into from
Aug 18, 2017
Merged

reduce buffer creation for ctr mode #48

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8 changes: 6 additions & 2 deletions aes.js
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Original file line number Diff line number Diff line change
Expand Up @@ -187,9 +187,13 @@ AES.prototype._reset = function () {
this._invKeySchedule = invKeySchedule
}

AES.prototype.encryptBlock = function (M) {
AES.prototype.encryptBlockRaw = function (M) {
M = asUInt32Array(M)
var out = cryptBlock(M, this._keySchedule, G.SUB_MIX, G.SBOX, this._nRounds)
return cryptBlock(M, this._keySchedule, G.SUB_MIX, G.SBOX, this._nRounds)
}

AES.prototype.encryptBlock = function (M) {
var out = this.encryptBlockRaw(M)
var buf = Buffer.allocUnsafe(16)
buf.writeUInt32BE(out[0], 0)
buf.writeUInt32BE(out[1], 4)
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2 changes: 1 addition & 1 deletion bench/index.js
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Expand Up @@ -5,7 +5,7 @@ let key = Buffer.alloc(16, 0xff)
let iv = Buffer.alloc(16, 0x01)

function test (mod, message) {
let cipher = mod.createCipheriv('aes-128-cbc', key, iv)
let cipher = mod.createCipheriv('aes-128-ctr', key, iv)
let b = cipher.update(message)
return Buffer.concat([b, cipher.final()])
}
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18 changes: 15 additions & 3 deletions modes/ctr.js
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Original file line number Diff line number Diff line change
Expand Up @@ -16,14 +16,26 @@ function incr32 (iv) {
}

function getBlock (self) {
var out = self._cipher.encryptBlock(self._prev)
var out = self._cipher.encryptBlockRaw(self._prev)
incr32(self._prev)
return out
}

var blockSize = 16
exports.encrypt = function (self, chunk) {
while (self._cache.length < chunk.length) {
self._cache = Buffer.concat([self._cache, getBlock(self)])
var chunkNum = Math.ceil(chunk.length / blockSize)
var start = self._cache.length
self._cache = Buffer.concat([
self._cache,
Buffer.allocUnsafe(chunkNum * blockSize)
])
for (var i = 0; i < chunkNum; i++) {
var out = getBlock(self)
var offset = start + i * blockSize
self._cache.writeUInt32BE(out[0], offset + 0)
self._cache.writeUInt32BE(out[1], offset + 4)
self._cache.writeUInt32BE(out[2], offset + 8)
self._cache.writeUInt32BE(out[3], offset + 12)
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Is this really better than a copy?

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The writeUint is not better, but the reason I am doing this is that it avoids creating intermediary buffers. Before encryptBlock creates a new buffer, fills it with those four values, just so that the buffer can be copied in here. By using the array directly there is now one less buffer allocation in the loop and together with the preallocation, no buffer allocations are in the loop.

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Nevermind, my mistake, I thought out was a Buffer.
ACK :)

}
var pad = self._cache.slice(0, chunk.length)
self._cache = self._cache.slice(chunk.length)
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