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77 lines
2.4 KiB
77 lines
2.4 KiB
// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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/*
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Package pbkdf2 implements the key derivation function PBKDF2 as defined in RFC
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2898 / PKCS #5 v2.0.
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A key derivation function is useful when encrypting data based on a password
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or any other not-fully-random data. It uses a pseudorandom function to derive
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a secure encryption key based on the password.
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While v2.0 of the standard defines only one pseudorandom function to use,
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HMAC-SHA1, the drafted v2.1 specification allows use of all five FIPS Approved
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Hash Functions SHA-1, SHA-224, SHA-256, SHA-384 and SHA-512 for HMAC. To
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choose, you can pass the `New` functions from the different SHA packages to
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pbkdf2.Key.
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*/
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package pbkdf2 // import "golang.org/x/crypto/pbkdf2"
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import (
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"crypto/hmac"
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"hash"
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)
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// Key derives a key from the password, salt and iteration count, returning a
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// []byte of length keylen that can be used as cryptographic key. The key is
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// derived based on the method described as PBKDF2 with the HMAC variant using
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// the supplied hash function.
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//
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// For example, to use a HMAC-SHA-1 based PBKDF2 key derivation function, you
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// can get a derived key for e.g. AES-256 (which needs a 32-byte key) by
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// doing:
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//
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// dk := pbkdf2.Key([]byte("some password"), salt, 4096, 32, sha1.New)
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//
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// Remember to get a good random salt. At least 8 bytes is recommended by the
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// RFC.
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//
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// Using a higher iteration count will increase the cost of an exhaustive
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// search but will also make derivation proportionally slower.
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func Key(password, salt []byte, iter, keyLen int, h func() hash.Hash) []byte {
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prf := hmac.New(h, password)
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hashLen := prf.Size()
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numBlocks := (keyLen + hashLen - 1) / hashLen
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var buf [4]byte
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dk := make([]byte, 0, numBlocks*hashLen)
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U := make([]byte, hashLen)
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for block := 1; block <= numBlocks; block++ {
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// N.B.: || means concatenation, ^ means XOR
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// for each block T_i = U_1 ^ U_2 ^ ... ^ U_iter
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// U_1 = PRF(password, salt || uint(i))
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prf.Reset()
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prf.Write(salt)
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buf[0] = byte(block >> 24)
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buf[1] = byte(block >> 16)
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buf[2] = byte(block >> 8)
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buf[3] = byte(block)
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prf.Write(buf[:4])
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dk = prf.Sum(dk)
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T := dk[len(dk)-hashLen:]
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copy(U, T)
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// U_n = PRF(password, U_(n-1))
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for n := 2; n <= iter; n++ {
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prf.Reset()
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prf.Write(U)
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U = U[:0]
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U = prf.Sum(U)
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for x := range U {
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T[x] ^= U[x]
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}
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}
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}
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return dk[:keyLen]
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}
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