Time-based one-time password algorithm: Difference between revisions

<lang csharp>using System;

using System.Security.Cryptography;

namespace RosettaTOTP

{

public class TOTP_SHA1

{

private byte[] K;

public TOTP_SHA1()

{

GenerateKey();

}

public void GenerateKey()

{

using (RandomNumberGenerator rng = new RNGCryptoServiceProvider())

{

/* Keys SHOULD be of the length of the HMAC output to facilitate

interoperability.*/

K = new byte[HMACSHA1.Create().HashSize];

rng.GetBytes(K);

}

}

public int HOTP(UInt64 C, int digits = 6)

{

var hmac = HMACSHA1.Create();

hmac.Key = K;

hmac.ComputeHash(BitConverter.GetBytes(C));

return Truncate(hmac.Hash, digits);

}

public UInt64 CounterNow(int T1 = 30)

{

var secondsSinceEpoch = (DateTime.UtcNow - new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)).TotalSeconds;

return (UInt64)Math.Floor(secondsSinceEpoch / T1);

}

private int DT(byte[] hmac_result)

{

int offset = hmac_result[19] & 0xf;

int bin_code = (hmac_result[offset] & 0x7f) << 24

| (hmac_result[offset + 1] & 0xff) << 16

| (hmac_result[offset + 2] & 0xff) << 8

| (hmac_result[offset + 3] & 0xff);

return bin_code;

}

private int Truncate(byte[] hmac_result, int digits)

{

var Snum = DT(hmac_result);

return Snum % (int)Math.Pow(10, digits);

}

}

class Program

{

static void Main(string[] args)

{

var totp = new TOTP_SHA1();

Console.WriteLine(totp.HOTP(totp.CounterNow()));

}

}

}

</lang>