Mail crypto

Usually the safest way to ensure that your e-mail won't be read by unauthorized persons is to encrypt them. To be compatible with the rest of the world I'd suggest to use free PGP software. PGP (Pretty Good Privacy) is a piece of software, used to ensure that a message/file has not been changed, has not been read, and comes from the person you think it comes from.

Download location: http://www.pgpi.org/

How does pgp Work? The whole idea behind PGP is that of Public and Private keys. To explain the algorithm PGP uses in order to encrypt the message would take too much time, and is beyond the scope of this, we will however look at how it ensures the integrity of the document. A user has a password, this password has to be chosen correctly, so don't choose passwords like "pop" or "iloveyou", this will make an attack more likely to succeed. The password is used to create a private key, and a public key - the algorithm ensures that you can not use the public key to make the private key.

The public key is sent to a server, or to the people you send e-mails/files, and you keep the private key secret. We will use a few terms and people in this introduction, they are: Pk - Public Key, Sk - Secret Key (private key). Adam will send an e-mail to Eve, and Rita will be a person in between, who we are trying to hide the content of the mail from. Rita will intercept the email (PGP doesn't ensure that Rita cant get her hands on the package, she can - its not a secure line like other technologies) and try to read it/modify it. Adam has a Sk1 and a Pk1, and Eve has a Sk2 and a Pk2. Both Adam, Eve, and Rita have Pk1 and Pk2, but Sk1 and Sk2 are presumed to be totally secret. First, here is a schematic of how it all looks:

PUBLIC SERVER Pk1, Pk2 Adam <------------------------------------------> Eve Sk1 ^ Sk2 | | | | Rita

So Adam wants to send a packet to Eve, without Rite reading it, or editing it. There are three things that we need to make sure:

That Rita cant read the text without permission That Rita cant edit it in any way, without Eve and Adam knowing

That Even knows that Adam sent it First thing is making sure Rita cant read the text. Adam does this by encrypting the message with Eves Pk2 which he has found on the server. You can only Encrypt with the Pk, not decrypt, so Rita wont be able to read the data unless Eve has revealed her Sk2.

The second thing to make sure, is that Rite cant edit the message. Adam creates a hash from the message he has created. The hash can be encrypted using Pk2, or sent as it is. When Eve gets the message, she decrypts it, and creates a hash herself, then checks if the hashes are the same - if they are, the message is the same, if its different, something has changed in the message. The Hash is very secure, and it is in theory impossible to make a change, and get the hash to remain the same.

The third, and probably one of the most important things to ensure, is that Rita hasn't grabbed the mail, made a new one, and sent it in Adams name. We can ensure this by using Public key and Private key too. The Sk can be used both to encrypt and to decrypt, but Pk can only encrypt. When Adam normally sends a message M to Eve, he creates the encrypted message C by doing: C=Pk2(M). This means, Adam uses Pk2 (Eves Pk) on message M to create message C. Image this: Adam can encrypt the message with his Sk1, because it is impossible to derive Sk1 from the message, this is secure and without any danger, as long as no one knows the password used to make Sk1 with. If the message M is encrypted with Sk1, he gets a message called X, Eve can decrypt the message using Pk1 which is public. If the message decrypts to something that makes sence, then it must be from Adam, because Sk1 is considered as secret, and only Adam knows it.

The entire process looks like this, when sending message C: Adam signs his digital signature on C, and hashes C: X=Sk1(C). Then Adam encrypts the message for Eve: M=Pk2(X). The message is sent, and looks all in all like this: M=Pk2(Sk1(C)). Rita can intercept M, but not decrypt, edit, or resend it. Eve receives M, and decrypts it: X=Sk2(M). Then she checks the digital signature: C=Pk1(X) and checks the Hash on the way.

This way, the PGP Public/Private key system ensures integrity and security of the document e-mail, but PGP is not the only algorithm that uses the Public/Private key theory, Blowfish, and RSA are among the many other technologies that use it, PGP is just the most popular for e-mail encryption, but many don't trust it because of rumors of backdoors by the NSA (I don't know if its true though). PGP comes in a commercial, and a freeware version for Windows, and is available for Linux as well. What ever encryption you use, it will be better than none.

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