Hot answers tagged length-extension
No, there is no known way. It would actually be rather surprising if there were even a theoretical way; the SHA-256 and the SHA-512 compression functions are rather different (for one, one works with 32 bit words and the other works with 64 bit words); one wouldn't expect them to share any sort of relation.
It seems that all this discussion about the IV is just to confuse the reader. Ignore IV. You just have to do a simple length-extension attack on the CBC-MAC. Yes, one message is enough.
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