In PHP I am RSA encrypting a message to be decrypted by .NET application... but I keep getting a "Bad Key" exception from .NET.... For RSA encryption, I am using PEAR class Crypt_RSA- encrypting with the public key (which is a modulus, exponent pair) I get from working encryption system in .NET... I guess the easiest question would be- does "Bad Key" mean it is not able to decrypt the message whatsoever? IE, it is not encrypted correctly? The harder question is- Is there anything specific about RSA encryption that causes quirks between .NET and PHP?