So, every time I (re)install a Mac-based system, I end up cursing horribly at Apple’s architects. Why? Because in the Apple World they seem to totally ignore the concept of files integrity, to such extent that it’s virtually impossible to get any assurance that the programs I install are in any way authentic (i.e. not tampered by some 3rd party, e.g. by somebody controlling my Internet connection).

Take any Apple installer package, e.g. Thunderbird. In most cases an installer package on Mac is a .dmg file, that represents an installation disk image. Now, when you open such a file under Mac, the OS will never display any information about if this file is somehow signed (e.g. by who) or not. In fact, I’m pretty sure it’s never signed. What you end up with, is a .dmg file that you just downloaded over plaintext HTTP and you have absolutely no way of verifying if it is the original file the vendor really published. And you’re just about to grant admin privileges to the installer program that is inside this file — after all it’s an installer, so must got root privileges, right (well, not quite maybe)? Beautiful…

Interestingly, this very same Thunderbird installer, but for Windows, is correctly signed, and Windows, correctly, displays that information (together with the ability to examine the certificate) and allows the user to make a choice of whether to allow it to run or not.

Disclosure :

Release of message contents to any person or process not processing the appropriate cryptographic key.

Traffic Analysis :

Discovery of patterns of traffic between parties. In a connection oriented- application, the frquency and duration of connection could be detemined. In either a connectionless environment, the number and length of message between parties could be determined.

Masquerade :

Insertion of message into the network from a fraudulent source. This includes the creation of messages by an opponent as if it has come from an authorized entity. It also includes fraudulent acknowledgements of message reciept or non-reciept by someone other than the message recipient.

Content Modification :

Changes to the contents of a message, including insertion, deletion, transposition and modification.

Sequence Modification :

Any modification to a sequence of messages between parties ,including insertion,deletion and recording.

• Pretty Good Privacy(PGP)
• Secure MIME(S/MIME)

Pretty Good Privacy(PGP) :

PGP provides a confidentiality and authentication service that can be used for electronic mail and file storage application. Philzimmerman is the father of the PGP protocol. He has done the following,

• Selected the best available cryptographic algorithms as building blocks.
• Integrated these algorithms into general purpose application that is independent of operating system and processor.
• Made the package, its documentation and source code available via the Internet.
• Entered into an agreement with Network associates to provide fully compatible, low cost version of PGP.

S/MIME Functionality :

In terms of general functionality , S/MIME is quite similiar to PGP. Like PGP, S/MIME provides for digital signatures and encryption of  Email messages. More specifically, S/MIME offers following functionalities.

Enveloped Data :

Consists of encrypted content of any type and encryption key encrypted with receiver’s public key.

Signed Data :

Consists of message digest encrypted with the sender’s private key. The content and digital signature are both Base-64 encoded.

Clear-Signed Data:

Similar to signed data. However, only the digital signature is Base-64 encoded.