private static byte[] OpenSSHPassphraseToKey(SecureString passphrase, byte[] iv, int length) {
const int HASH_SIZE = 16;
const int SALT_SIZE = 8;
var md5 = new MD5CryptoServiceProvider();
//var pp = Encoding.UTF8.GetBytes(passphrase);
var buf = new byte[((length + HASH_SIZE - 1) / HASH_SIZE) * HASH_SIZE];
var offset = 0;
while (offset < length) {
if (offset > 0)
md5.TransformBlock(buf, 0, offset, null, 0);
//md5.TransformBlock(pp, 0, pp.Length, null, 0);
md5.HashBlock(passphrase, false);
md5.TransformFinalBlock(iv, 0, SALT_SIZE);
Buffer.BlockCopy(md5.Hash, 0, buf, offset, HASH_SIZE);
offset += HASH_SIZE;
md5.Initialize();
}
md5.Clear();
var key = new byte[length];
Buffer.BlockCopy(buf, 0, key, 0, length);
return key;
}