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68 lines
2.2 KiB
Go
68 lines
2.2 KiB
Go
/*
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* Copyright (c) 2015, Yawning Angel <yawning at schwanenlied dot me>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* * Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* * Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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package scramblesuit
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import (
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"crypto/hmac"
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"hash"
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)
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func hkdfExpand(hashFn func() hash.Hash, prk []byte, info []byte, l int) []byte {
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// Why, yes. golang.org/x/crypto/hkdf exists, and is a fine
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// implementation of HKDF. However it does both the extract
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// and expand, while ScrambleSuit only does extract, with no
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// way to separate the two steps.
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h := hmac.New(hashFn, prk)
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digestSz := h.Size()
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if l > 255*digestSz {
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panic("hkdf: requested OKM length > 255*HashLen")
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}
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var t []byte
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okm := make([]byte, 0, l)
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toAppend := l
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ctr := byte(1)
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for toAppend > 0 {
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h.Reset()
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_, _ = h.Write(t)
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_, _ = h.Write(info)
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_, _ = h.Write([]byte{ctr})
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t = h.Sum(nil)
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ctr++
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aLen := digestSz
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if toAppend < digestSz {
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aLen = toAppend
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}
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okm = append(okm, t[:aLen]...)
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toAppend -= aLen
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}
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return okm
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}
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