I don't think you know what you are talking about. If your authentication is implicit in the decryption of the messages, replaying that data will accomplish nothing.

For example, if I share a secret "password" with my server, I can do this in javascript using any symmetric cipher:

    ToServer: "My name is oconnore"
    ToClient: cipher(iv1, "(C1) Hi oconnore. Use this! iv2=rng()"++msghash, "password")
    ToServer: cipher(iv2, "(C2) Thanks, give me my data please!"++msghash, "password")
    ToClient: cipher(iv3, "(C3) <Some data>, and iv4=rng()"++msghash, "password")
    ...

If an attacker repeats any of these messages, the client/server will discard them based on the counter. Of course, for real use you would need to use public key crypto to avoid storing passwords in what is essentially plaintext, but I thought this would illustrate how replay attacks are a non issue.

Of course, as noted before, all this is irrelevant if you are sending your code over a channel vulnerable to MITM...