BouncyCastleRSA

Public Function Encrypt(data As Byte(), key As AsymmetricKeyParameter) As Byte()
    Dim engine = New RsaEngine()
    engine.Init(True, key)
    Dim blockSize = engine.GetInputBlockSize()
    Return engine.ProcessBlock(data, 0, blockSize)
End Function

Public Function Decrypt(data As Byte(), key As AsymmetricKeyParameter) As Byte()
    Dim engine = New RsaEngine()
    engine.Init(False, key)
    Dim blockSize = engine.GetInputBlockSize()
    Return engine.ProcessBlock(data, 0, blockSize)
End Function