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'use strict';
var createHash = require('create-hash/browser');
var inherits = require('inherits')
var Transform = require('stream').Transform
var ZEROS = new Buffer(128)
ZEROS.fill(0)
function Hmac(alg, key) {
Transform.call(this)
alg = alg.toLowerCase()
if (typeof key === 'string') {
key = new Buffer(key)
}
var blocksize = (alg === 'sha512' || alg === 'sha384') ? 128 : 64
this._alg = alg
this._key = key
if (key.length > blocksize) {
key = createHash(alg).update(key).digest()
} else if (key.length < blocksize) {
key = Buffer.concat([key, ZEROS], blocksize)
}
var ipad = this._ipad = new Buffer(blocksize)
var opad = this._opad = new Buffer(blocksize)
for (var i = 0; i < blocksize; i++) {
ipad[i] = key[i] ^ 0x36
opad[i] = key[i] ^ 0x5C
}
this._hash = createHash(alg).update(ipad)
}
inherits(Hmac, Transform)
Hmac.prototype.update = function (data, enc) {
this._hash.update(data, enc)
return this
}
Hmac.prototype._transform = function (data, _, next) {
this._hash.update(data)
next()
}
Hmac.prototype._flush = function (next) {
this.push(this.digest())
next()
}
Hmac.prototype.digest = function (enc) {
var h = this._hash.digest()
return createHash(this._alg).update(this._opad).update(h).digest(enc)
}
module.exports = function createHmac(alg, key) {
return new Hmac(alg, key)
}
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