hkdf.go

     1  // Copyright 2024 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package hkdf
     6  
     7  import (
     8  	"crypto/internal/fips140"
     9  	"crypto/internal/fips140/hmac"
    10  	"hash"
    11  )
    12  
    13  func Extract[H hash.Hash](h func() H, secret, salt []byte) []byte {
    14  	if len(secret) < 112/8 {
    15  		fips140.RecordNonApproved()
    16  	}
    17  	if salt == nil {
    18  		salt = make([]byte, h().Size())
    19  	}
    20  	extractor := hmac.New(h, salt)
    21  	hmac.MarkAsUsedInKDF(extractor)
    22  	extractor.Write(secret)
    23  
    24  	return extractor.Sum(nil)
    25  }
    26  
    27  func Expand[H hash.Hash](h func() H, pseudorandomKey []byte, info string, keyLen int) []byte {
    28  	out := make([]byte, 0, keyLen)
    29  	expander := hmac.New(h, pseudorandomKey)
    30  	hmac.MarkAsUsedInKDF(expander)
    31  	var counter uint8
    32  	var buf []byte
    33  
    34  	for len(out) < keyLen {
    35  		counter++
    36  		if counter == 0 {
    37  			panic("hkdf: counter overflow")
    38  		}
    39  		if counter > 1 {
    40  			expander.Reset()
    41  		}
    42  		expander.Write(buf)
    43  		expander.Write([]byte(info))
    44  		expander.Write([]byte{counter})
    45  		buf = expander.Sum(buf[:0])
    46  		remain := keyLen - len(out)
    47  		remain = min(remain, len(buf))
    48  		out = append(out, buf[:remain]...)
    49  	}
    50  
    51  	return out
    52  }
    53  
    54  func Key[H hash.Hash](h func() H, secret, salt []byte, info string, keyLen int) []byte {
    55  	prk := Extract(h, secret, salt)
    56  	return Expand(h, prk, info, keyLen)
    57  }
    58
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