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							- var Buffer = require('safe-buffer').Buffer
 
- var checkParameters = require('./precondition')
 
- var defaultEncoding = require('./default-encoding')
 
- var sync = require('./sync')
 
- var toBuffer = require('./to-buffer')
 
- var ZERO_BUF
 
- var subtle = global.crypto && global.crypto.subtle
 
- var toBrowser = {
 
-   sha: 'SHA-1',
 
-   'sha-1': 'SHA-1',
 
-   sha1: 'SHA-1',
 
-   sha256: 'SHA-256',
 
-   'sha-256': 'SHA-256',
 
-   sha384: 'SHA-384',
 
-   'sha-384': 'SHA-384',
 
-   'sha-512': 'SHA-512',
 
-   sha512: 'SHA-512'
 
- }
 
- var checks = []
 
- function checkNative (algo) {
 
-   if (global.process && !global.process.browser) {
 
-     return Promise.resolve(false)
 
-   }
 
-   if (!subtle || !subtle.importKey || !subtle.deriveBits) {
 
-     return Promise.resolve(false)
 
-   }
 
-   if (checks[algo] !== undefined) {
 
-     return checks[algo]
 
-   }
 
-   ZERO_BUF = ZERO_BUF || Buffer.alloc(8)
 
-   var prom = browserPbkdf2(ZERO_BUF, ZERO_BUF, 10, 128, algo)
 
-     .then(function () {
 
-       return true
 
-     }).catch(function () {
 
-       return false
 
-     })
 
-   checks[algo] = prom
 
-   return prom
 
- }
 
- var nextTick
 
- function getNextTick () {
 
-   if (nextTick) {
 
-     return nextTick
 
-   }
 
-   if (global.process && global.process.nextTick) {
 
-     nextTick = global.process.nextTick
 
-   } else if (global.queueMicrotask) {
 
-     nextTick = global.queueMicrotask
 
-   } else if (global.setImmediate) {
 
-     nextTick = global.setImmediate
 
-   } else {
 
-     nextTick = global.setTimeout
 
-   }
 
-   return nextTick
 
- }
 
- function browserPbkdf2 (password, salt, iterations, length, algo) {
 
-   return subtle.importKey(
 
-     'raw', password, { name: 'PBKDF2' }, false, ['deriveBits']
 
-   ).then(function (key) {
 
-     return subtle.deriveBits({
 
-       name: 'PBKDF2',
 
-       salt: salt,
 
-       iterations: iterations,
 
-       hash: {
 
-         name: algo
 
-       }
 
-     }, key, length << 3)
 
-   }).then(function (res) {
 
-     return Buffer.from(res)
 
-   })
 
- }
 
- function resolvePromise (promise, callback) {
 
-   promise.then(function (out) {
 
-     getNextTick()(function () {
 
-       callback(null, out)
 
-     })
 
-   }, function (e) {
 
-     getNextTick()(function () {
 
-       callback(e)
 
-     })
 
-   })
 
- }
 
- module.exports = function (password, salt, iterations, keylen, digest, callback) {
 
-   if (typeof digest === 'function') {
 
-     callback = digest
 
-     digest = undefined
 
-   }
 
-   digest = digest || 'sha1'
 
-   var algo = toBrowser[digest.toLowerCase()]
 
-   if (!algo || typeof global.Promise !== 'function') {
 
-     getNextTick()(function () {
 
-       var out
 
-       try {
 
-         out = sync(password, salt, iterations, keylen, digest)
 
-       } catch (e) {
 
-         return callback(e)
 
-       }
 
-       callback(null, out)
 
-     })
 
-     return
 
-   }
 
-   checkParameters(iterations, keylen)
 
-   password = toBuffer(password, defaultEncoding, 'Password')
 
-   salt = toBuffer(salt, defaultEncoding, 'Salt')
 
-   if (typeof callback !== 'function') throw new Error('No callback provided to pbkdf2')
 
-   resolvePromise(checkNative(algo).then(function (resp) {
 
-     if (resp) return browserPbkdf2(password, salt, iterations, keylen, algo)
 
-     return sync(password, salt, iterations, keylen, digest)
 
-   }), callback)
 
- }
 
 
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