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Asked: 2026-05-30T01:57:26+00:00

I faced a strange issue when I am decrypting a zip stream. After I

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I faced a strange issue when I am decrypting a zip stream.

After I decrypted the given stream I have exactly the same array of bytes apart from 8 bytes of header.

It should be 50 4B 03 04 (according to Zip spec) but I get different.

When I decrypt the same stream in c# the header is correct. I use RijndaelManaged, mode CBC, padding ZeroBytePadding, and block size = 128

In Java I use AES/CBC/NoPadding block size=128 to decrypt.

I believe the cause is padding but then I don’t understand why the rest of bytes are correct.

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1 Answer

  1. Editorial Team

    In CBC mode, the padding mode should only affect the last bytes of your message, not the first ones (i.e. from ZeroBytePadding to NoPadding you might get some added 0 bytes at the end).

    If your first block is different (but the rest matches), the most probable cause is a different initialization vector in encryption and decryption. Check this.

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