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pbkdf.go
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pbkdf.go
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package pbkdf
import (
"hash"
"bytes"
"math/big"
)
// implementation of https://tools.ietf.org/html/rfc7292#appendix-B.2 , RFC text verbatim in comments
// Let H be a hash function built around a compression function f:
// Z_2^u x Z_2^v -> Z_2^u
// (that is, H has a chaining variable and output of length u bits, and
// the message input to the compression function of H is v bits). The
// values for u and v are as follows:
// HASH FUNCTION VALUE u VALUE v
// MD2, MD5 128 512
// SHA-1 160 512
// SHA-224 224 512
// SHA-256 256 512
// SHA-384 384 1024
// SHA-512 512 1024
// SHA-512/224 224 1024
// SHA-512/256 256 1024
// Furthermore, let r be the iteration count.
// We assume here that u and v are both multiples of 8, as are the
// lengths of the password and salt strings (which we denote by p and s,
// respectively) and the number n of pseudorandom bits required. In
// addition, u and v are of course non-zero.
// For information on security considerations for MD5 [19], see [25] and
// [1], and on those for MD2, see [18].
// The following procedure can be used to produce pseudorandom bits for
// a particular "purpose" that is identified by a byte called "ID".
// This standard specifies 3 different values for the ID byte:
// 1. If ID=1, then the pseudorandom bits being produced are to be used
// as key material for performing encryption or decryption.
// 2. If ID=2, then the pseudorandom bits being produced are to be used
// as an IV (Initial Value) for encryption or decryption.
// 3. If ID=3, then the pseudorandom bits being produced are to be used
// as an integrity key for MACing.
// 1. Construct a string, D (the "diversifier"), by concatenating v/8
// copies of ID.
var one = big.NewInt(1)
func Key(h func() hash.Hash, u, v int, salt, password []byte, r int, ID byte, size int) (key []byte) {
var D []byte
for i := 0; i < v; i++ {
D = append(D, ID)
}
S := fillWithRepeats(salt, v)
P := fillWithRepeats(password, v)
I := append(S, P...)
c := (size + u - 1) / u
A := make([]byte, c*u)
var IjBuf []byte
for i := 0; i < c; i++ {
Ai := hashFunc(h, append(D, I...))
for j := 1; j < r; j++ {
Ai = hashFunc(h, Ai)
}
copy(A[i*u:], Ai[:])
if i < c-1 {
var B []byte
for len(B) < v {
B = append(B, Ai[:]...)
}
B = B[:v]
{
Bbi := new(big.Int).SetBytes(B)
Ij := new(big.Int)
for j := 0; j < len(I)/v; j++ {
Ij.SetBytes(I[j*v : (j+1)*v])
Ij.Add(Ij, Bbi)
Ij.Add(Ij, one)
Ijb := Ij.Bytes()
if len(Ijb) > v {
Ijb = Ijb[len(Ijb)-v:]
}
if len(Ijb) < v {
if IjBuf == nil {
IjBuf = make([]byte, v)
}
bytesShort := v - len(Ijb)
for i := 0; i < bytesShort; i++ {
IjBuf[i] = 0
}
copy(IjBuf[bytesShort:], Ijb)
Ijb = IjBuf
}
copy(I[j*v:(j+1)*v], Ijb)
}
}
}
}
return A[:size]
}
// 单个加密
func hashFunc(h func() hash.Hash, key []byte) []byte {
fn := h()
fn.Write(key)
data := fn.Sum(nil)
return data
}
func fillWithRepeats(pattern []byte, v int) []byte {
if len(pattern) == 0 {
return nil
}
outputLen := v * ((len(pattern) + v - 1) / v)
return bytes.Repeat(pattern, (outputLen+len(pattern)-1)/len(pattern))[:outputLen]
}