Add encrypt & decrypt using zip standard encryption

zipcrypto.go

@@ -0,0 +1,110 @@
+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))
+	//z.fw.FileHeader.CompressedSize += uint32(n)
+	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
+}