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  )
    11  
    12  func Extract[H fips140.Hash](h func() H, secret, salt []byte) []byte {
    13  	if len(secret) < 112/8 {
    14  		fips140.RecordNonApproved()
    15  	}
    16  	if salt == nil {
    17  		salt = make([]byte, h().Size())
    18  	}
    19  	extractor := hmac.New(h, salt)
    20  	hmac.MarkAsUsedInKDF(extractor)
    21  	extractor.Write(secret)
    22  
    23  	return extractor.Sum(nil)
    24  }
    25  
    26  func Expand[H fips140.Hash](h func() H, pseudorandomKey []byte, info string, keyLen int) []byte {
    27  	out := make([]byte, 0, keyLen)
    28  	expander := hmac.New(h, pseudorandomKey)
    29  	hmac.MarkAsUsedInKDF(expander)
    30  	var counter uint8
    31  	var buf []byte
    32  
    33  	for len(out) < keyLen {
    34  		counter++
    35  		if counter == 0 {
    36  			panic("hkdf: counter overflow")
    37  		}
    38  		if counter > 1 {
    39  			expander.Reset()
    40  		}
    41  		expander.Write(buf)
    42  		expander.Write([]byte(info))
    43  		expander.Write([]byte{counter})
    44  		buf = expander.Sum(buf[:0])
    45  		remain := keyLen - len(out)
    46  		remain = min(remain, len(buf))
    47  		out = append(out, buf[:remain]...)
    48  	}
    49  
    50  	return out
    51  }
    52  
    53  func Key[H fips140.Hash](h func() H, secret, salt []byte, info string, keyLen int) []byte {
    54  	prk := Extract(h, secret, salt)
    55  	return Expand(h, prk, info, keyLen)
    56  }
    57
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