53 lines
1.5 KiB
Go
53 lines
1.5 KiB
Go
|
/*
|
||
|
|
HKDF is a simple key derivation function (KDF) based on
|
||
|
|
a hash-based message authentication code (HMAC). It was initially proposed by its authors as a building block in
|
||
|
|
various protocols and applications, as well as to discourage the proliferation of multiple KDF mechanisms.
|
||
|
|
The main approach HKDF follows is the "extract-then-expand" paradigm, where the KDF logically consists of two modules:
|
||
|
|
the first stage takes the input keying material and "extracts" from it a fixed-length pseudorandom key, and then the
|
||
|
|
second stage "expands" this key into several additional pseudorandom keys (the output of the KDF).
|
||
|
|
*/
|
||
|
|
package hkdf
|
||
|
|
|
||
|
|
import (
|
||
|
|
"crypto/hmac"
|
||
|
|
"crypto/sha256"
|
||
|
|
"fmt"
|
||
|
|
"golang.org/x/crypto/hkdf"
|
||
|
|
"io"
|
||
|
|
)
|
||
|
|
|
||
|
|
/*
|
||
|
|
Expand expands a given key with the HKDF algorithm.
|
||
|
|
*/
|
||
|
|
func Expand(key []byte, length int, info string) ([]byte, error) {
|
||
|
|
if info == "" {
|
||
|
|
keyBlock := hmac.New(sha256.New, key)
|
||
|
|
var out, last []byte
|
||
|
|
|
||
|
|
var blockIndex byte = 1
|
||
|
|
for i := 0; len(out) < length; i++ {
|
||
|
|
keyBlock.Reset()
|
||
|
|
//keyBlock.Write(append(append(last, []byte(info)...), blockIndex))
|
||
|
|
keyBlock.Write(last)
|
||
|
|
keyBlock.Write([]byte(info))
|
||
|
|
keyBlock.Write([]byte{blockIndex})
|
||
|
|
last = keyBlock.Sum(nil)
|
||
|
|
blockIndex += 1
|
||
|
|
out = append(out, last...)
|
||
|
|
}
|
||
|
|
return out[:length], nil
|
||
|
|
} else {
|
||
|
|
h := hkdf.New(sha256.New, key, nil, []byte(info))
|
||
|
|
out := make([]byte, length)
|
||
|
|
n, err := io.ReadAtLeast(h, out, length)
|
||
|
|
if err != nil {
|
||
|
|
return nil, err
|
||
|
|
}
|
||
|
|
if n != length {
|
||
|
|
return nil, fmt.Errorf("new key to short")
|
||
|
|
}
|
||
|
|
|
||
|
|
return out[:length], nil
|
||
|
|
}
|
||
|
|
}
|