forked from mirror/zip
109 lines
2.2 KiB
Go
109 lines
2.2 KiB
Go
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package zip
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import (
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"io"
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"bytes"
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"hash/crc32"
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)
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type ZipCrypto struct {
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password []byte
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Keys [3]uint32
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}
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func NewZipCrypto(passphrase []byte) *ZipCrypto {
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z := &ZipCrypto{}
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z.password = passphrase
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z.init()
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return z
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}
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func (z *ZipCrypto) init() {
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z.Keys[0] = 0x12345678
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z.Keys[1] = 0x23456789
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z.Keys[2] = 0x34567890
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for i := 0; i < len(z.password); i++ {
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z.updateKeys(z.password[i])
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}
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}
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func (z *ZipCrypto) updateKeys(byteValue byte) {
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z.Keys[0] = crc32update(z.Keys[0], byteValue);
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z.Keys[1] += z.Keys[0] & 0xff;
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z.Keys[1] = z.Keys[1] * 134775813 + 1;
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z.Keys[2] = crc32update(z.Keys[2], (byte) (z.Keys[1] >> 24));
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}
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func (z *ZipCrypto) magicByte() byte {
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var t uint32 = z.Keys[2] | 2
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return byte((t * (t ^ 1)) >> 8)
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}
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func (z *ZipCrypto) Encrypt(data []byte) []byte {
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length := len(data)
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chiper := make([]byte, length)
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for i := 0; i < length; i++ {
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v := data[i]
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chiper[i] = v ^ z.magicByte()
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z.updateKeys(v)
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}
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return chiper
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}
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func (z *ZipCrypto) Decrypt(chiper []byte) []byte {
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length := len(chiper)
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plain := make([]byte, length)
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for i, c := range chiper {
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v := c ^ z.magicByte();
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z.updateKeys(v)
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plain[i] = v
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}
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return plain
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}
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func crc32update(pCrc32 uint32, bval byte) uint32 {
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return crc32.IEEETable[(pCrc32 ^ uint32(bval)) & 0xff] ^ (pCrc32 >> 8)
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}
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func ZipCryptoDecryptor(r *io.SectionReader, password []byte) (*io.SectionReader, error) {
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z := NewZipCrypto(password)
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b := make([]byte, r.Size())
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r.Read(b)
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m := z.Decrypt(b)
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return io.NewSectionReader(bytes.NewReader(m), 12, int64(len(m))), nil
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}
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type zipCryptoWriter struct {
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w io.Writer
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z *ZipCrypto
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first bool
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fw *fileWriter
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}
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func (z *zipCryptoWriter) Write(p []byte) (n int, err error) {
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err = nil
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if z.first {
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z.first = false
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header := []byte{0xF8, 0x53, 0xCF, 0x05, 0x2D, 0xDD, 0xAD, 0xC8, 0x66, 0x3F, 0x8C, 0xAC}
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header = z.z.Encrypt(header)
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crc := z.fw.ModifiedTime
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header[10] = byte(crc)
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header[11] = byte(crc >> 8)
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z.z.init()
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z.w.Write(z.z.Encrypt(header))
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n += 12
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}
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z.w.Write(z.z.Encrypt(p))
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return
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}
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func ZipCryptoEncryptor(i io.Writer, pass passwordFn, fw *fileWriter) (io.Writer, error) {
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z := NewZipCrypto(pass())
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zc := &zipCryptoWriter{i, z, true, fw}
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return zc, nil
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}
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