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// Copyright 2014 Matthew Endsley
// All rights reserved
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted providing that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// 2. 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.
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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 keywrap is an implementation of the RFC 3394 AES key wrapping
// algorithm. This is used in OpenPGP with elliptic curve keys.
package keywrap
import (
"crypto/aes"
"encoding/binary"
"errors"
)
var (
// ErrWrapPlaintext is returned if the plaintext is not a multiple
// of 64 bits.
ErrWrapPlaintext = errors.New("keywrap: plainText must be a multiple of 64 bits")
// ErrUnwrapCiphertext is returned if the ciphertext is not a
// multiple of 64 bits.
ErrUnwrapCiphertext = errors.New("keywrap: cipherText must by a multiple of 64 bits")
// ErrUnwrapFailed is returned if unwrapping a key fails.
ErrUnwrapFailed = errors.New("keywrap: failed to unwrap key")
// NB: the AES NewCipher call only fails if the key is an invalid length.
// ErrInvalidKey is returned when the AES key is invalid.
ErrInvalidKey = errors.New("keywrap: invalid AES key")
)
// Wrap a key using the RFC 3394 AES Key Wrap Algorithm.
func Wrap(key, plainText []byte) ([]byte, error) {
if len(plainText)%8 != 0 {
return nil, ErrWrapPlaintext
}
c, err := aes.NewCipher(key)
if err != nil {
return nil, ErrInvalidKey
}
nblocks := len(plainText) / 8
// 1) Initialize variables.
var block [aes.BlockSize]byte
// - Set A = IV, an initial value (see 2.2.3)
for ii := 0; ii < 8; ii++ {
block[ii] = 0xA6
}
// - For i = 1 to n
// - Set R[i] = P[i]
intermediate := make([]byte, len(plainText))
copy(intermediate, plainText)
// 2) Calculate intermediate values.
for ii := 0; ii < 6; ii++ {
for jj := 0; jj < nblocks; jj++ {
// - B = AES(K, A | R[i])
copy(block[8:], intermediate[jj*8:jj*8+8])
c.Encrypt(block[:], block[:])
// - A = MSB(64, B) ^ t where t = (n*j)+1
t := uint64(ii*nblocks + jj + 1)
val := binary.BigEndian.Uint64(block[:8]) ^ t
binary.BigEndian.PutUint64(block[:8], val)
// - R[i] = LSB(64, B)
copy(intermediate[jj*8:jj*8+8], block[8:])
}
}
// 3) Output results.
// - Set C[0] = A
// - For i = 1 to n
// - C[i] = R[i]
return append(block[:8], intermediate...), nil
}
// Unwrap a key using the RFC 3394 AES Key Wrap Algorithm.
func Unwrap(key, cipherText []byte) ([]byte, error) {
if len(cipherText)%8 != 0 {
return nil, ErrUnwrapCiphertext
}
c, err := aes.NewCipher(key)
if err != nil {
return nil, ErrInvalidKey
}
nblocks := len(cipherText)/8 - 1
// 1) Initialize variables.
var block [aes.BlockSize]byte
// - Set A = C[0]
copy(block[:8], cipherText[:8])
// - For i = 1 to n
// - Set R[i] = C[i]
intermediate := make([]byte, len(cipherText)-8)
copy(intermediate, cipherText[8:])
// 2) Compute intermediate values.
for jj := 5; jj >= 0; jj-- {
for ii := nblocks - 1; ii >= 0; ii-- {
// - B = AES-1(K, (A ^ t) | R[i]) where t = n*j+1
// - A = MSB(64, B)
t := uint64(jj*nblocks + ii + 1)
val := binary.BigEndian.Uint64(block[:8]) ^ t
binary.BigEndian.PutUint64(block[:8], val)
copy(block[8:], intermediate[ii*8:ii*8+8])
c.Decrypt(block[:], block[:])
// - R[i] = LSB(B, 64)
copy(intermediate[ii*8:ii*8+8], block[8:])
}
}
// 3) Output results.
// - If A is an appropriate initial value (see 2.2.3),
for ii := 0; ii < 8; ii++ {
if block[ii] != 0xA6 {
return nil, ErrUnwrapFailed
}
}
// - For i = 1 to n
// - P[i] = R[i]
return intermediate, nil
}
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