zip/zipcrypto.go

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