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//
// Copyright (c) 2017 anygone contributors (see AUTHORS file)
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright notice, this
// list of conditions and the following disclaimer.
//
// * Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
// and/or other materials provided with the distribution.
//
// * Neither the name of anygone nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
package satp
import (
"crypto/aes"
"crypto/cipher"
"crypto/subtle"
"encoding/binary"
"errors"
"strconv"
)
const (
AES_CTR_KD_SALT_LENGTH = aes.BlockSize - 2 // two bytes spare for counter
)
type AESCTRKeyDerivation struct {
cipher cipher.Block
salt []byte
role KDRole
}
func (kd *AESCTRKeyDerivation) generateCTR(dir Direction, usage KeyUsage, sequenceNumber uint32, ctr []byte) {
ctr[aes.BlockSize-1] = 0
ctr[aes.BlockSize-2] = 0
subtle.ConstantTimeCopy(1, ctr[:len(kd.salt)], kd.salt)
keyID := [8]byte{}
binary.BigEndian.PutUint32(keyID[:4], getKDLabel(kd.role, dir, usage))
binary.BigEndian.PutUint32(keyID[4:], sequenceNumber)
// unfortunately crypto.xorBytes is not exported...
offset := len(kd.salt) - len(keyID)
n := len(keyID)
for i := 0; i < n; i++ {
ctr[offset+i] = ctr[offset+i] ^ keyID[i]
}
}
func (kd *AESCTRKeyDerivation) Generate(dir Direction, usage KeyUsage, sequenceNumber uint32, out []byte) error {
// this needs to stay in this function so that the go compiler can detect that it doesn't escape
// from this function and whence will get allocated on the stack
ctr := [aes.BlockSize]byte{}
kd.generateCTR(dir, usage, sequenceNumber, ctr[:])
for i := range out { // unfortunately there is no memset-style function in go...
out[i] = 0
}
c := cipher.NewCTR(kd.cipher, ctr[:])
c.XORKeyStream(out, out)
return nil
}
func NewAESCTRKeyDerivation(key, salt []byte, role KDRole) (KeyDerivation, error) {
if len(salt) != AES_CTR_KD_SALT_LENGTH {
return nil, errors.New("invalid salt size: " + strconv.Itoa(len(salt)))
}
kd := &AESCTRKeyDerivation{salt: salt, role: role}
var err error
if kd.cipher, err = aes.NewCipher(key); err != nil {
return nil, err
}
return kd, nil
}
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