private void _EmitOne(System.IO.Stream outstream, out ZipCrypto cipher)
{
// If PKZip (weak) encryption is in use, then the entry data is preceded by
// 12-byte "encryption header" for the entry.
byte[] encryptionHeader = null;
cipher = null;
if (_Password != null && Encryption == EncryptionAlgorithm.PkzipWeak)
{
cipher = new ZipCrypto();
// apply the password to the keys
cipher.InitCipher(_Password);
// generate the random 12-byte header:
var rnd = new System.Random();
encryptionHeader = new byte[12];
rnd.NextBytes(encryptionHeader);
// Here, it is important to encrypt the random header, INCLUDING the final byte
// which is the high-order byte of the CRC32. We must do this before
// we encrypt the file data. This step changes the state of the cipher, or in the
// words of the PKZIP spec, it "further initializes" the cipher keys.
// No way around this: must read the stream to compute the actual CRC
FigureCrc32();
encryptionHeader[11] = (byte)((this._Crc32 >> 24) & 0xff);
byte[] cipherText = cipher.EncryptMessage(encryptionHeader, encryptionHeader.Length);
// Write the ciphered bonafide encryption header.
outstream.Write(cipherText, 0, cipherText.Length);
}
// write the (potentially compressed, potentially encrypted) file data
_WriteFileData(cipher, outstream);
_TotalEntrySize = _LengthOfHeader + _CompressedSize;
}
