Using a one-time pad with a block cipher
Well, no.

What you are describing is ECB mode of operation. ECB mode of operation is insecure as repeats of plaintext blocks leads to repeats of ciphertext blocks. This is a leak of information so it breaks confidentiality. So even if you would leak less information because of key reuse, you would still leak information if it happens.

Furthermore it is possible to find out if a key is (likely) correct by validating a ciphertext block against partial information within plaintext blocks. To that breaks the perfect secrecy provided by a One Time Pad.



I'll try and explain that last section further.

Note that there aren't $2^n$ possible permutations, there are $2^n!$ possible permutations. To be perfectly secure you should allow each one of them (with the same probability, no less).

That would mean that for any sensible $n$ the key size would grow out of proportion. Furthermore, you would have to have a cipher that would map all those keys to exactly one permutation, something that is not true for usual block ciphers.

So even if you have a key of n bits with m &lt; n bits of known plaintext then it is likely that you can tell with a probability higher than $0.5$ if it is the correct one or not, breaking perfect secrecy for the remaining n - m bits.