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I'm trying to figure out how padding works by seeing what happens when I try to encrypt a 16 byte file with AES-128-CBC. My understanding was if I encrypt a file of size, say, 28, then there would automatically be 4 bytes of padding to make it 32. But when I encrypted my 16-byte file, the size ended up being 48 bytes. I did research and learned that a single padding block is automatically added to direct multiples in order to distinguish the padding from the plaintext, but if that's so, then why is it 48 bytes and not 32 as well (16 plaintext + 16 padding)?

Alyssa June
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Is your "-K" in the code in uppercase or lowercase? If it is in lowercase, the encryption will automatically add a salt value into your cipher text, causing it to have more than 32 bytes. CBC will pad it until it reaches 48 bytes later(the multiplication of 16).

Aaron Lieu
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