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We are using the below cipher
AES/ECB/NOPADDING
But I am little confused because modes like ECB need the input to be padded according to the block size.But here we say NOPADDING.Dont they look contradictory.
Can we have arbitrary data which is not padded as input to ECB mode.
The “raw” modes of ECB encryption with no padding applied like for example AES/ECB/NOPADDING, are basically the pure application of the encryption function to N blocks of data. They are useful for developers that need to implement custom modes that are not shipped by default. Any mode of operation is somehow constructed from the raw encryption function.
Still, since a block cipher can only operate on full-length blocks, some form of padding has may have to be applied on the last block. This is left up to the developer, they will implement whatever form of padding is specified/recommended for the mode they wish to implement. There are many possibilities, and this is why we have “NOPADDING” – to leave the choice of padding up to us.
These modes, XXX/ECB/NOPADDING, should never be used directly. Neither should any ECB mode, really. Plain ECB encryption is very insecure, for example it doesn’t hide statistical properties of the plaintext (you may know the examples where the “encrypted” image still looks much like the original). On top of that, as already noted, a block cipher can only operate on full-length blocks. This requires applying a custom padding scheme, which would add another layer where mistakes can be made as opposed to simply relying on some default implementation.