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Is there a difference in terms of security between
An encrypted stream of bits obtained by encrypting a plaintext concatenated with it's signature
$ C = E_k(plaintext||\sigma)$
where $E$ is a symmetric or asymmetric encryption function, II is a concatenation operator and
where $h$ is a secure MAC (the key is assumed to be the same).
A bit stream obtained by concatenating a ciphertext and the signature over the its corresponding plaintext
A stream obtained by encrypting the ciphertext of the plaintext concatenated with the signature over the respective ciphertext
Also, is there any risk due to using the same key for both encrypting and signing? I don't refer to the cases that do not involve recovering the key through other means other than passive or active attacks.