Can Decrypt[] be forced to decrypt with a different key?

Question

Decrypt[] will yield an error if one tries to decrypt a byte array using a different symmetric key than the one used to encrypt:

Decrypt[key2, Encrypt[key1, "foobar"]["Data"]]
> [..] Decrypt: Data could not be decrypted
> $Failed

I want to be able to mathematically perform the decrypt operation on a byte array and get a byte array even if the key doesn't match, for example, in 3DES. How can I force Decrypt to not yield a message and return the "decrypted" bytes? How does it even know that the decryption is correct or not with no knowledge of the plaintext bytes?

Answer 1

From the documentation:

Encrypt[key,"string"] yields an EncryptedObject containing the encrypted version of the contents of the string as encoded in UTF-8.

So the decrypted string must be valid UTF-8. However:

Encrypt[key,ByteArray[...]] yields an EncryptedObject containing the encrypted version of the raw bytes in the ByteArray object.

so if the encrypted thing is a ByteArray, it may work.