AES vs RSA - Which is stronger given two scenarios? Let's say we have some plaintext.
Let's say that we encrypt this plaintext with a random 32 byte key using AES-256.
Let's say that we also encrypt this plaintext with an RSA 2048 public key.

If only the cipher text was known, which of these would be harder to identify the plaintext from?

My thoughts are that it would be the RSA ciphertext since the assumption is that the attacker has no access to either the public key or the private key, just the ciphertext. This is because the attacker has nothing to base any assumptions on and would still have to figure out what the private key is.
It is also assumed that an attacker doesn't know anything about the secret key used as input to the AES algorithm.

Now lets assume that for either algorithm a mode of operation is used that sufficiently protects the ciphertext (say AES-CTR and RSA-OAEP). Then it comes down to analysing the security of the cipher itself given the key size.

Neither AES nor RSA has been broken in the sense that it is much less secure than the strength it was designed for. The key size is therefore easy: AES-256 has close to 256 bits of security while RSA only offers about 112 bits of security. In that respect AES-256 has RSA-2048 completely beat.

As for the algorithm, AES-256 is considered secure against analysis with quantum computers. RSA is definitely not, given a large enough quantum computer. The only disadvantage of AES is that there is no security proof of the algorithm itself. We suppose it is secure, but we're not certain. RSA probably has a slightly better mathematical problem behind it.

Operationally speaking: it is much more likely that AES is implemented / executed correctly rather than RSA.



All in all I'd strongly recommend AES given your question.

But in the end recommending one over the other is futile; an asymmetric cipher has different properties and should be used in different scenarios than a symmetric cipher.

Say for instance that the system that performs the encryption is not as secure as the system that does the decryption. In that case RSA is a much better fit than AES as RSA encryption only requires the public key to be present.

Distributing a public key is of course also a completely different fish than sharing an AES secret key. With a public key you can distribute freely as long as the receiver can trust the public key. With AES you need a secure channel in advance.