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/*-
* Copyright 2014 Square Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package josecipher
import (
"crypto/cipher"
"crypto/subtle"
"encoding/binary"
"errors"
)
var defaultIV = []byte{0xA6, 0xA6, 0xA6, 0xA6, 0xA6, 0xA6, 0xA6, 0xA6}
// KeyWrap implements NIST key wrapping; it wraps a content encryption key (cek) with the given block cipher.
func KeyWrap(block cipher.Block, cek []byte) ([]byte, error) {
if len(cek)%8 != 0 {
return nil, errors.New("square/go-jose: key wrap input must be 8 byte blocks")
}
n := len(cek) / 8
r := make([][]byte, n)
for i := range r {
r[i] = make([]byte, 8)
copy(r[i], cek[i*8:])
}
buffer := make([]byte, 16)
tBytes := make([]byte, 8)
copy(buffer, defaultIV)
for t := 0; t < 6*n; t++ {
copy(buffer[8:], r[t%n])
block.Encrypt(buffer, buffer)
binary.BigEndian.PutUint64(tBytes, uint64(t+1))
for i := 0; i < 8; i++ {
buffer[i] = buffer[i] ^ tBytes[i]
}
copy(r[t%n], buffer[8:])
}
out := make([]byte, (n+1)*8)
copy(out, buffer[:8])
for i := range r {
copy(out[(i+1)*8:], r[i])
}
return out, nil
}
// KeyUnwrap implements NIST key unwrapping; it unwraps a content encryption key (cek) with the given block cipher.
func KeyUnwrap(block cipher.Block, ciphertext []byte) ([]byte, error) {
if len(ciphertext)%8 != 0 {
return nil, errors.New("square/go-jose: key wrap input must be 8 byte blocks")
}
n := (len(ciphertext) / 8) - 1
r := make([][]byte, n)
for i := range r {
r[i] = make([]byte, 8)
copy(r[i], ciphertext[(i+1)*8:])
}
buffer := make([]byte, 16)
tBytes := make([]byte, 8)
copy(buffer[:8], ciphertext[:8])
for t := 6*n - 1; t >= 0; t-- {
binary.BigEndian.PutUint64(tBytes, uint64(t+1))
for i := 0; i < 8; i++ {
buffer[i] = buffer[i] ^ tBytes[i]
}
copy(buffer[8:], r[t%n])
block.Decrypt(buffer, buffer)
copy(r[t%n], buffer[8:])
}
if subtle.ConstantTimeCompare(buffer[:8], defaultIV) == 0 {
return nil, errors.New("square/go-jose: failed to unwrap key")
}
out := make([]byte, n*8)
for i := range r {
copy(out[i*8:], r[i])
}
return out, nil
}
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