public static int PaddingSizeForMethod(PaddingAlgorithm paddingMethod)
{
switch (paddingMethod)
{
case PaddingAlgorithm.None: return(0);
case PaddingAlgorithm.PKCS1: return(RsaPkcs1PaddingSize);
case PaddingAlgorithm.PKCS1_OAEP: return(RsaPkcs1OaepPaddingSize);
}
throw new Exception();
}
public static int CalculateEncryptedSize(X509Certificate2 cert, int messageSize,
PaddingAlgorithm paddingAlgorithm)
{
var rsa = cert.PublicKey.Key as RSA;
if (rsa == null)
{
throw new Exception("Could not create RSA");
}
int pad = PaddingSizeForMethod(paddingAlgorithm);
int keySize = CalculatePublicKeyLength(cert) / 8;
if (keySize < pad)
{
throw new Exception();
}
int blockSize = keySize - pad;
int numBlocks = (messageSize + blockSize - 1) / blockSize;
return(numBlocks * keySize);
}