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48 lines
1.4 KiB
Go
48 lines
1.4 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/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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var h io.Reader
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if info == "" {
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/*
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Only used during initial login
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Pseudorandom Key is provided by server and has not to be created
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*/
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h = hkdf.Expand(sha256.New, key, []byte(info))
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} else {
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/*
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Used every other time
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Pseudorandom Key is created during kdf.New
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This is the normal that crypto/hkdf is used
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*/
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h = hkdf.New(sha256.New, key, nil, []byte(info))
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}
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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, nil
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}
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