/// <summary>
/// Creates a secret key with the specified number of bits of entropy and specified
/// <see cref="CryptoSecureRequirement"/> to be shared with the user on wich the future valid TOTP codes will
/// be based.
/// </summary>
/// <param name="bits">The number of bits of entropy to use.</param>
/// <param name="cryptoSecureRequirement">The <see cref="CryptoSecureRequirement"/> to ensure cryptographically secure RNG's.</param>
/// <returns>
/// Returns a string of random values in 'Base32 alphabet' to be shared with the user / stored with the account.
/// </returns>
/// <exception cref="CryptographicException">
/// Thrown when the <see cref="IRngProvider"/> of the instance is not cryptographically secure and the
/// <see cref="CryptoSecureRequirement"/> requires a cryptographically secure RNG.
/// </exception>
public string CreateSecret(int bits, CryptoSecureRequirement cryptoSecureRequirement)
{
if (cryptoSecureRequirement == CryptoSecureRequirement.RequireSecure && !RngProvider.IsCryptographicallySecure)
{
throw new CryptographicException("RNG provider is not cryptographically secure");
}
int bytes = (int)Math.Ceiling((double)bits / 5); // We use 5 bits of each byte (since we have a
// 32-character 'alphabet' / base32)
// Note that we DO NOT actually "base32 encode" the random bytes, we simply take 5 bits from each random
// byte and map these directly to letters from the base32 alphabet (effectively 'base32 encoding on the fly').
return(string.Concat(RngProvider.GetRandomBytes(bytes).Select(v => Base32.Base32Alphabet[v & 31])));
}
/// <summary>
/// Creates a secret key with the specified number of bits of entropy and specified
/// <see cref="CryptoSecureRequirement"/> to be shared with the user on wich the future valid TOTP codes will
/// be based.
/// </summary>
/// <param name="bits">The number of bits of entropy to use.</param>
/// <param name="cryptoSecureRequirement">The <see cref="CryptoSecureRequirement"/> to ensure cryptographically secure RNG's.</param>
/// <returns>
/// Returns a string of random values in 'Base32 alphabet' to be shared with the user / stored with the account.
/// </returns>
/// <exception cref="CryptographicException">
/// Thrown when the <see cref="IRngProvider"/> of the instance is not cryptographically secure and the
/// <see cref="CryptoSecureRequirement"/> requires a cryptographically secure RNG.
/// </exception>
public string CreateSecret(int bits, CryptoSecureRequirement cryptoSecureRequirement)
{
if (cryptoSecureRequirement == CryptoSecureRequirement.RequireSecure && !this.RngProvider.IsCryptographicallySecure)
throw new CryptographicException("RNG provider is not cryptographically secure");
int bytes = (int)Math.Ceiling((double)bits / 5); // We use 5 bits of each byte (since we have a
// 32-character 'alphabet' / base32)
// Note that we DO NOT actually "base32 encode" the random bytes, we simply take 5 bits from each random
// byte and map these directly to letters from the base32 alphabet (effectively 'base32 encoding on the fly').
return string.Concat(this.RngProvider.GetRandomBytes(bytes).Select(v => Base32.Base32Alphabet[v & 31]));
}
