58 lines
1.7 KiB
Go
58 lines
1.7 KiB
Go
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// Copyright (c) 2016, Google Inc.
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice appear in all copies.
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//
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// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
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package runner
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import (
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"crypto/hmac"
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"hash"
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)
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// hkdfExtract implements HKDF-Extract from RFC 5869.
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func hkdfExtract(hash func() hash.Hash, salt, ikm []byte) []byte {
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if salt == nil {
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salt = make([]byte, hash().Size())
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}
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hmac := hmac.New(hash, salt)
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hmac.Write(ikm)
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return hmac.Sum(nil)
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}
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// hkdfExpand implements HKDF-Expand from RFC 5869.
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func hkdfExpand(hash func() hash.Hash, prk, info []byte, length int) []byte {
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hashSize := hash().Size()
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if length > 255*hashSize {
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panic("hkdfExpand: length too long")
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}
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if len(prk) < hashSize {
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panic("hkdfExpand: prk too short")
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}
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var lastBlock []byte
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counter := byte(0)
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okm := make([]byte, length)
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hmac := hmac.New(hash, prk)
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for length > 0 {
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hmac.Reset()
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counter++
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hmac.Write(lastBlock)
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hmac.Write(info)
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hmac.Write([]byte{counter})
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block := hmac.Sum(nil)
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lastBlock = block
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copy(okm[(int(counter)-1)*hashSize:], block)
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length -= hashSize
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}
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return okm
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}
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