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29 lines
693 B
Go
29 lines
693 B
Go
// Package kdf implements ShangMi(SM) used Key Derivation Function, compliances with GB/T 32918.4-2016 5.4.3.
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package kdf
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import (
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"encoding/binary"
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"hash"
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)
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// Kdf key derivation function, compliance with GB/T 32918.4-2016 5.4.3.
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// ANSI-X9.63-KDF
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func Kdf(md hash.Hash, z []byte, len int) []byte {
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limit := uint64(len+md.Size()-1) / uint64(md.Size())
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if limit >= uint64(1<<32)-1 {
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panic("kdf: key length too long")
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}
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var countBytes [4]byte
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var ct uint32 = 1
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var k []byte
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for i := 0; i < int(limit); i++ {
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binary.BigEndian.PutUint32(countBytes[:], ct)
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md.Write(z)
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md.Write(countBytes[:])
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k = md.Sum(k)
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ct++
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md.Reset()
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}
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return k[:len]
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}
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