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