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