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89 lines
1.9 KiB
89 lines
1.9 KiB
var Buffer = require('safe-buffer').Buffer
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var ZEROES = Buffer.alloc(16, 0)
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function toArray (buf) {
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return [
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buf.readUInt32BE(0),
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buf.readUInt32BE(4),
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buf.readUInt32BE(8),
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buf.readUInt32BE(12)
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]
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}
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function fromArray (out) {
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var buf = Buffer.allocUnsafe(16)
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buf.writeUInt32BE(out[0] >>> 0, 0)
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buf.writeUInt32BE(out[1] >>> 0, 4)
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buf.writeUInt32BE(out[2] >>> 0, 8)
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buf.writeUInt32BE(out[3] >>> 0, 12)
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return buf
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}
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function GHASH (key) {
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this.h = key
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this.state = Buffer.alloc(16, 0)
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this.cache = Buffer.allocUnsafe(0)
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}
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// from http://bitwiseshiftleft.github.io/sjcl/doc/symbols/src/core_gcm.js.html
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// by Juho Vähä-Herttua
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GHASH.prototype.ghash = function (block) {
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var i = -1
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while (++i < block.length) {
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this.state[i] ^= block[i]
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}
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this._multiply()
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}
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GHASH.prototype._multiply = function () {
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var Vi = toArray(this.h)
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var Zi = [0, 0, 0, 0]
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var j, xi, lsbVi
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var i = -1
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while (++i < 128) {
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xi = (this.state[~~(i / 8)] & (1 << (7 - (i % 8)))) !== 0
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if (xi) {
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// Z_i+1 = Z_i ^ V_i
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Zi[0] ^= Vi[0]
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Zi[1] ^= Vi[1]
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Zi[2] ^= Vi[2]
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Zi[3] ^= Vi[3]
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}
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// Store the value of LSB(V_i)
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lsbVi = (Vi[3] & 1) !== 0
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// V_i+1 = V_i >> 1
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for (j = 3; j > 0; j--) {
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Vi[j] = (Vi[j] >>> 1) | ((Vi[j - 1] & 1) << 31)
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}
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Vi[0] = Vi[0] >>> 1
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// If LSB(V_i) is 1, V_i+1 = (V_i >> 1) ^ R
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if (lsbVi) {
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Vi[0] = Vi[0] ^ (0xe1 << 24)
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}
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}
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this.state = fromArray(Zi)
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}
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GHASH.prototype.update = function (buf) {
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this.cache = Buffer.concat([this.cache, buf])
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var chunk
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while (this.cache.length >= 16) {
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chunk = this.cache.slice(0, 16)
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this.cache = this.cache.slice(16)
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this.ghash(chunk)
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}
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}
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GHASH.prototype.final = function (abl, bl) {
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if (this.cache.length) {
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this.ghash(Buffer.concat([this.cache, ZEROES], 16))
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}
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this.ghash(fromArray([0, abl, 0, bl]))
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return this.state
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}
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module.exports = GHASH
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