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Generate random bytes for TripleDES key C#

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c#

tripledes

I need to generate byte array for TripleDES encryption. I don't want to use .generateKey() because I need to know the bytes in the key to pass them to another application.

Thanks for the replies but I forgot to mention one thing: the bytes have to be odd parity. Otherwise I can't generate a TripleDES key from them. I'm not so familiar with the odd parity, so I guess have to create a byte check if it has odd parity or not; then if it does put it in the array, otherwise not.

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hs2d Avatar asked Mar 18 '11 07:03

hs2d


3 Answers

If you need to ensure the odd parity, you have to compute it yourself. This should do:

var rng = new RNGCryptoServiceProvider();
var key = new byte[24];
rng.GetBytes(key);

for(var i = 0; i < key.Length; ++i)
{
    int keyByte = key[i] & 0xFE;
    var parity = 0;
    for (var b = keyByte; b != 0; b >>= 1) parity ^= b & 1;
    key[i] = (byte)(keyByte | (parity == 0 ? 1 : 0));
}

return key;
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Mormegil Avatar answered Nov 20 '22 21:11

Mormegil


How about:

RandomNumberGenerator rng = RandomNumberGenerator.Create();
byte[] key = new byte[24]; // For a 192-bit key
rng.GetBytes(key);

tripleDes.Key = key;

Note that RandomNumberGenerator is suitable for crypto work (in terms of reasonably secure, hard-to-predict random data), whereas System.Random isn't.

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Jon Skeet Avatar answered Nov 20 '22 23:11

Jon Skeet


But ... what's the problem with just:

TripleDES provider = TripleDES.Create();

byte[] key = provider.Key;

There you get your key used by the en- and decryptor created with this instance.

Note that the other answers lack a TripleDES.IsWeakKey.

like image 2
ordag Avatar answered Nov 20 '22 21:11

ordag