Implement MDC-using encryption

[singpolyma]

In response to singpolyma/openpgp-php#17
In an attempt to close #18

Code based on https://github.com/singpolyma/openpgp-php

[DanielRuf]

Awesome, thanks. Much appreciated. Will test it tomorrow and merge it then.

@jasonhinkle please check if none of the unittests are broken.

[DanielRuf]

It does not work here, gpg --list-packets says the file was manipulated:

gpg: Warnung: Verschlüsselte Botschaft ist manipuliert worden!

Encrypted TESTMESSAGETEXT and got this result:

:encrypted data packet:
        length: 81
        mdc_method: 2
:literal data packet:
        mode t (74), created 0, name="file",
        raw data: 15 bytes
:mdc packet: length=20
gpg: Warnung: Verschlüsselte Botschaft ist manipuliert worden!

[singpolyma]

@DanielRuf Ah yes, there was a bug in the padding handling because of the resync change. Fixed now.

[DanielRuf]

👍 great, works here now =)

@jasonhinkle please test on your side. We have to add this also to the dev branch. Should we increment the version to 1.6.0?

[jasonhinkle]

Hey @DanielRuf , I don't have a client to test this with - is it possible to write a unit test to verify that it works?

[DanielRuf]

is it possible to write a unit test to verify that it works?

Probably not yet until we have decryption implemented as we have to decrypt, then use the length from the MDC packet and use it to get the prefix and the SHA-1 hash. With this and the decrypted cleartext message we can check if it is correct (hash the cleartext and the prefix and check it with the hash from the decrypted message).

This would be the right way.