Validating key size for a SymmetricAlgorithm

SymmetricEncryption.cs

// in a method
// alorithm = SymmetricAlgorithm
// keySize  = int (in bits)

if (algorithm.ValidKeySize(keySize))
{
    algorithm.KeySize = keySize;
}
else
{
    throw new ArgumentException(
      String.Format("{0} bits is not a valid key size for {1}. Valid key sizes: {2}", 
        keySize, algorithm.GetType().Name, GetFormattedKeySizes(algorithm)), "keySize");
}

// in the SymmetricEncryption class

/// <summary>
/// Returns a comma-separated list of key sizes for a given algorithm
/// </summary>
/// <param name="algorithm">Algorithm to use</param>
/// <returns></returns>
private static string GetFormattedKeySizes(SymmetricAlgorithm algorithm)
{
    var keySizes = new List<int>();

    foreach(var keySize in algorithm.LegalKeySizes)
    {
        // Max, min, skip
        for (var i = keySize.MinSize; i <= keySize.MaxSize; i += keySize.SkipSize)
        {
            keySizes.Add(i);
        }
    }

    return String.Join(", ", keySizes.Distinct().OrderBy(i => i).Select(i => i + " bits"));
}