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var zeros = new Buffer(16)
zeros.fill(0)
module.exports = GHASH
function GHASH (key) {
this.h = key
this.state = new Buffer(16)
this.state.fill(0)
this.cache = new Buffer('')
}
// from http://bitwiseshiftleft.github.io/sjcl/doc/symbols/src/core_gcm.js.html
// by Juho Vähä-Herttua
GHASH.prototype.ghash = function (block) {
var i = -1
while (++i < block.length) {
this.state[i] ^= block[i]
}
this._multiply()
}
GHASH.prototype._multiply = function () {
var Vi = toArray(this.h)
var Zi = [0, 0, 0, 0]
var j, xi, lsb_Vi
var i = -1
while (++i < 128) {
xi = (this.state[~~(i / 8)] & (1 << (7 - i % 8))) !== 0
if (xi) {
// Z_i+1 = Z_i ^ V_i
Zi = xor(Zi, Vi)
}
// Store the value of LSB(V_i)
lsb_Vi = (Vi[3] & 1) !== 0
// V_i+1 = V_i >> 1
for (j = 3; j > 0; j--) {
Vi[j] = (Vi[j] >>> 1) | ((Vi[j - 1] & 1) << 31)
}
Vi[0] = Vi[0] >>> 1
// If LSB(V_i) is 1, V_i+1 = (V_i >> 1) ^ R
if (lsb_Vi) {
Vi[0] = Vi[0] ^ (0xe1 << 24)
}
}
this.state = fromArray(Zi)
}
GHASH.prototype.update = function (buf) {
this.cache = Buffer.concat([this.cache, buf])
var chunk
while (this.cache.length >= 16) {
chunk = this.cache.slice(0, 16)
this.cache = this.cache.slice(16)
this.ghash(chunk)
}
}
GHASH.prototype.final = function (abl, bl) {
if (this.cache.length) {
this.ghash(Buffer.concat([this.cache, zeros], 16))
}
this.ghash(fromArray([
0, abl,
0, bl
]))
return this.state
}
function toArray (buf) {
return [
buf.readUInt32BE(0),
buf.readUInt32BE(4),
buf.readUInt32BE(8),
buf.readUInt32BE(12)
]
}
function fromArray (out) {
out = out.map(fixup_uint32)
var buf = new Buffer(16)
buf.writeUInt32BE(out[0], 0)
buf.writeUInt32BE(out[1], 4)
buf.writeUInt32BE(out[2], 8)
buf.writeUInt32BE(out[3], 12)
return buf
}
var uint_max = Math.pow(2, 32)
function fixup_uint32 (x) {
var ret, x_pos
ret = x > uint_max || x < 0 ? (x_pos = Math.abs(x) % uint_max, x < 0 ? uint_max - x_pos : x_pos) : x
return ret
}
function xor (a, b) {
return [
a[0] ^ b[0],
a[1] ^ b[1],
a[2] ^ b[2],
a[3] ^ b[3]
]
}
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