gtsocial-umbx

pbkdf2.go (2483B)

---

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