Adds support AES decryption #579
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| amount_to_read -= BLOCK_SIZE | ||
| @counter += 1 | ||
| end | ||
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We are missing the check of the CRC, we should check that the decrypted content hasn't been tampered.
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I've tried to integrate the AES integrity check, but it doesn't work.
If you have an idea, I'd love to hear it.
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I've finally found the problem, I've finished the implementation and I'm going to write the tests.
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Hi @hainesr, What do you think about merging this first version without integrating the integrity test? |
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Hi @hainesr, ready for review. |
| return unless @decrypter.kind_of?(::Zip::AESDecrypter) | ||
| return unless input_finished? | ||
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| @decrypter.check_integrity(@io.read(::Zip::AESEncryption::AUTHENTICATION_CODE_LENGTH)) |
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I am not sure that this line fully respects the specification, when checking integrity of the file, with VERSION_AE_1 we should use the CRC field while with VERSION_AE_2 it should use the authentication code which is byte-aligned.
I do not fully understand your code, but I found nothing like this.
See https://www.winzip.com/en/support/aes-encryption/#CRC:
## CRC value
For files encrypted using the AE-2 method, the standard Zip CRC value is not used, and a 0 must be stored in this field. Corruption of encrypted data within a Zip file is instead detected via the [authentication code](https://www.winzip.com/en/support/aes-encryption/#authentication-code) field.
Files encrypted using the AE-1 method do include the standard Zip CRC value. This, along with the fact that the vendor version stored in the AES extra data field is 0x0001 for AE-1 and 0x0002 for AE-2, is the only difference between the AE-1 and AE-2 formats.
NOTE: Zip utilities that support the AE-2 format are required to be able to read files that were created in the AE-1 format, and during decryption/extraction of files in AE-1 format should verify that the file's CRC matches the value stored in the CRC field.There was a problem hiding this comment.
I'll look into it in the next few days, thx.
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@Ph0tonic I reread the spec and the integrity check must be performed in all cases.
The only difference is that with AE-1, you also get a CRC
| @key_length = KEY_LENGTHS[@strength] | ||
| @salt_length = SALT_LENGTHS[@strength] | ||
| end | ||
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If we had decryption, we should also implement encryption. This would provide a way to test the full stack.
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I'm not going to have time to implement encryption
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Hi all, Many, many thanks for this work, and many, many apologies for taking so long to acknowledge it. I will try and look at this as soon as possible. I won't be able to include it in version 3 - I really just need to get that out, it's been dragging on too long as it is - but as this is added functionality we should be safe to release this in version 3.1. Thanks, |
#573 #179 @Ph0tonic