Symmetric encryption - options?

[jpemail2001-321 at yahoo.com]

>It isn't RSA because this is symmetric encryption.  CAST5 is a 128-bit block cypher.
So its not really safe, is it?

@Robert 

>If you choose to use someone's public certificate to encrypt a message,
>they use the private part of that certificate to decrypt it -- different
>things for encryption and decryption, thus a different kind of
>algorithm, an asymmetric one, is used.So you would suggest, to use RSA? I think so because it seems to be stronger encryption.

The problem is I need to encrypt a message but I dont know the recipient yet. So I considered a passphrase method.
Cause he dont need to send me his public key (if he has any). 

But.... OK I will try to encrypt the message with a new created private key (specially created for the recipient) which I will send later to him, so he will be able to decrypt the message. A bit complicated but possible, I think!? ^^
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