/// <summary>
/// Checks if the file signature is valid.
/// </summary>
/// <param name="data">Original, decrypted file in raw format.</param>
/// <param name="userId">Id of the user decrypting the file.</param>
/// <param name="ownerPublicKey">Public RSA key of the file owner used to verify file signature.</param>
/// <returns>true if the signature is valid, otherwise false.</returns>
private bool CheckFileSignature(byte[] data, int userId, RSAParameters ownerPublicKey)
{
try
{
var hashAlgo = AlgorithmUtility.GetHashAlgoFromNameSignature(((SecurityDescriptor)Headers[1]).HashAlgorithmName);
return(CheckFileSignatureHelper(data, userId, ownerPublicKey, hashAlgo));
}
catch (CryptographicException)
{
var hashAlgo = AlgorithmUtility.GetHashSignerFromNameSignature(((SecurityDescriptor)Headers[1]).HashAlgorithmName);
return(CheckFileSignatureHelper(data, userId, ownerPublicKey, hashAlgo));
}
}
/// <summary>
/// Creates a file signature using the unencripted data and user private RSA key.
/// </summary>
/// <param name="data">Original, unencrypted file in raw format.</param>
/// <param name="userPrivateKey">Private RSA key of the user encrypting the file.</param>
private void SignFile(byte[] data, ref RSAParameters userPrivateKey)
{
try
{
// Exception will be thrown if the hashing algoritm is MD2, MD4, RIPEMD or SHA224.
var hashAlgo = AlgorithmUtility.GetHashAlgoFromNameSignature(((SecurityDescriptor)Headers[1]).HashAlgorithmName);
((SecurityDescriptor)Headers[1]).Signature = new RsaAlgorithm(userPrivateKey).CreateSignature(data, hashAlgo);
}
catch (CryptographicException)
{
var hashAlgo = AlgorithmUtility.GetHashSignerFromNameSignature(((SecurityDescriptor)Headers[1]).HashAlgorithmName);
((SecurityDescriptor)Headers[1]).Signature = new RsaAlgorithm(userPrivateKey).CreateSignature(data, hashAlgo);
}
}