83 lines
2.4 KiB
Go
83 lines
2.4 KiB
Go
// This package is used to implement Key Derivation Functions (KDF)
|
|
// based on the recommendations of NIST SP 800-108. These are useful
|
|
// for generating unique-per-transaction keys, or situations in which
|
|
// a key hierarchy may be useful.
|
|
package kdf
|
|
|
|
import (
|
|
"crypto/hmac"
|
|
"crypto/sha256"
|
|
"encoding/binary"
|
|
"fmt"
|
|
"math"
|
|
)
|
|
|
|
// PRF is a pseudo-random function that takes a key or seed,
|
|
// as well as additional binary data and generates output that is
|
|
// indistinguishable from random. Examples are cryptographic hash
|
|
// functions or block ciphers.
|
|
type PRF func([]byte, []byte) ([]byte, error)
|
|
|
|
// CounterMode implements the counter mode KDF that uses a pseudo-random-function (PRF)
|
|
// along with a counter to generate derived keys. The KDF takes a base key
|
|
// a derivation context, and the required number of output bits.
|
|
func CounterMode(prf PRF, prfLen uint32, key []byte, context []byte, bits uint32) ([]byte, error) {
|
|
// Ensure the PRF is byte aligned
|
|
if prfLen%8 != 0 {
|
|
return nil, fmt.Errorf("PRF must be byte aligned")
|
|
}
|
|
|
|
// Ensure the bits required are byte aligned
|
|
if bits%8 != 0 {
|
|
return nil, fmt.Errorf("bits required must be byte aligned")
|
|
}
|
|
|
|
// Determine the number of rounds required
|
|
rounds := bits / prfLen
|
|
if bits%prfLen != 0 {
|
|
rounds++
|
|
}
|
|
|
|
if len(context) > math.MaxInt-8 {
|
|
return nil, fmt.Errorf("too much context specified; would overflow: %d bytes", len(context))
|
|
}
|
|
|
|
// Allocate and setup the input
|
|
input := make([]byte, 4+len(context)+4)
|
|
copy(input[4:], context)
|
|
binary.BigEndian.PutUint32(input[4+len(context):], bits)
|
|
|
|
// Iteratively generate more key material
|
|
var out []byte
|
|
var i uint32
|
|
for i = 0; i < rounds; i++ {
|
|
// Update the counter in the input string
|
|
binary.BigEndian.PutUint32(input[:4], i)
|
|
|
|
// Compute more key material
|
|
part, err := prf(key, input)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
if uint32(len(part)*8) != prfLen {
|
|
return nil, fmt.Errorf("PRF length mis-match (%d vs %d)", len(part)*8, prfLen)
|
|
}
|
|
out = append(out, part...)
|
|
}
|
|
|
|
// Return the desired number of output bytes
|
|
return out[:bits/8], nil
|
|
}
|
|
|
|
const (
|
|
// HMACSHA256PRFLen is the length of output from HMACSHA256PRF
|
|
HMACSHA256PRFLen uint32 = 256
|
|
)
|
|
|
|
// HMACSHA256PRF is a pseudo-random-function (PRF) that uses an HMAC-SHA256
|
|
func HMACSHA256PRF(key []byte, data []byte) ([]byte, error) {
|
|
hash := hmac.New(sha256.New, key)
|
|
hash.Write(data)
|
|
return hash.Sum(nil), nil
|
|
}
|