If a ciphertext has length $n$ and a key $k$ decrypts it to a plaintext that makes sense only in the first $n-k$ characters, where the $k$ last ones are random looking --- then it's not plausible that it's correct.
To achieve different lengths one could have a padding scheme and a block size larger than one character. However, then it must still fit the padding.
If a ciphertext has length $n$ and a key $k$ decrypts it to a plaintext that makes sense only in the first $n-k$ characters, where the $k$ last ones are random looking --- then it's not plausible that it's correct.
To achieve different lengths one could have a padding scheme and a block size larger than one character. However, then it must still fit the padding.